11-cis-retinal and Night-Blindness

Vision in dim-light conditions is triggered by photoactivation of rhodopsin, the visual pigment of rod photoreceptor cells. Rhodopsin is made of a protein, the G protein coupled receptor (GPCR) opsin, and the chromophore 11-cis-retinal. Vertebrate rod opsin is the GPCR best characterized at the atomic level of detail. Since the release of the first crystal structure 20 years ago, a huge number of structures have been released that, in combination with valuable spectroscopic determinations, unveiled most aspects of the photobleaching process. A number of spontaneous mutations of rod opsin have been found linked to vision-impairing diseases like autosomal dominant or autosomal recessive retinitis pigmentosa (adRP or arRP, respectively) and autosomal congenital stationary night blindness (adCSNB). While adCSNB is mainly caused by constitutive activation of rod opsin, RP shows more variegate determinants affecting different aspects of rod opsin function. The vast majority of missense rod opsin mutations affects folding and trafficking and is linked to adRP, an incurable disease that awaits light on its molecular structure determinants. This review article summarizes all major structural information available on vertebrate rod opsin conformational states and the insights gained so far into the structural determinants of adCSNB and adRP linked to rod opsin mutations. Strategies to design small chaperones with therapeutic potential for selected adRP rod opsin mutants will be discussed as well.

Topics: Animals; Crystallography, X-Ray; Eye Diseases, Hereditary; Genetic Diseases, X-Linked; Humans; Myopia; Night Blindness; Protein Structure, Secondary; Retinitis Pigmentosa; Rhodopsin

Retinitis pigmentosa (RP) is an inherited retinal dystrophy caused by the loss of photoreceptors and characterized by retinal pigment deposits visible on fundus examination. Prevalence of non syndromic RP is approximately 1/4,000. The most common form of RP is a rod-cone dystrophy, in which the first symptom is night blindness, followed by the progressive loss in the peripheral visual field in daylight, and eventually leading to blindness after several decades. Some extreme cases may have a rapid evolution over two decades or a slow progression that never leads to blindness. In some cases, the clinical presentation is a cone-rod dystrophy, in which the decrease in visual acuity predominates over the visual field loss. RP is usually non syndromic but there are also many syndromic forms, the most frequent being Usher syndrome. To date, 45 causative genes/loci have been identified in non syndromic RP (for the autosomal dominant, autosomal recessive, X-linked, and digenic forms). Clinical diagnosis is based on the presence of night blindness and peripheral visual field defects, lesions in the fundus, hypovolted electroretinogram traces, and progressive worsening of these signs. Molecular diagnosis can be made for some genes, but is not usually performed due to the tremendous genetic heterogeneity of the disease. Genetic counseling is always advised. Currently, there is no therapy that stops the evolution of the disease or restores the vision, so the visual prognosis is poor. The therapeutic approach is restricted to slowing down the degenerative process by sunlight protection and vitaminotherapy, treating the complications (cataract and macular edema), and helping patients to cope with the social and psychological impact of blindness. However, new therapeutic strategies are emerging from intensive research (gene therapy, neuroprotection, retinal prosthesis).

Topics: Adolescent; Child; Child, Preschool; Diagnosis, Differential; Female; Humans; Infant; Metabolic Diseases; Nervous System Diseases; Night Blindness; Pregnancy; Prenatal Diagnosis; Prognosis; Retinal Rod Photoreceptor Cells; Retinitis Pigmentosa; Rhodopsin; Sensation Disorders; Syndrome

Topics: Animals; Disease Models, Animal; Genes, Dominant; Genetic Therapy; Mice; Mice, Transgenic; Mutation; Night Blindness; Retinal Diseases; Retinitis Pigmentosa; Rhodopsin

Rhodopsin is the membrane receptor responsible for photoreception in the vertebrate retina. Its characteristic seven-transmembrane helical structural motif is today widely recognised as a paradigm in signal transduction. Rhodopsin and the phototransduction system are frequently used as structural and mechanistic models for the G-protein coupled receptor superfamily. Recent advances in the activation mechanism (as derived from the structural available data) and the implications for normal and pathological - in retinal disorders - visual function will be reviewed.

Topics: Amino Acid Sequence; Animals; Humans; Models, Molecular; Molecular Sequence Data; Mutation; Night Blindness; Protein Structure, Secondary; Retinal Diseases; Retinitis Pigmentosa; Rhodopsin; Vision, Ocular

Although rhodopsin's role in activating the phototransduction cascade is well known, the processes that deactivate rhodopsin, and thus the rest of the cascade, are less well understood. At least three proteins appear to play a role: rhodopsin kinase, arrestin and recoverin. Here we review recent physiological studies of the molecular mechanisms of rhodopsin deactivation. The approach was to monitor the light responses of individual mouse rods in which rhodopsin was altered or arrestin was deleted by transgenic techniques. Removal of rhodopsin's carboxy-terminal residues which contain phosphorylation sites implicated in deactivation, prolonged the flash response 20-fold and caused it to become highly variable. In rods that did not express arrestin the flash response recovered partially, but final recovery was slowed over 100-fold. These results are consistent with the notion that phosphorylation initiates rhodopsin deactivation and that arrestin binding completes the process. The stationary night blindness of Oguchi disease, associated with null mutations in the genes for arrestin or rhodopsin kinase, presumably results from impaired rhodopsin deactivation, like that revealed by the experiments on transgenic animals.

Topics: Animals; Arrestin; Eye Proteins; G-Protein-Coupled Receptor Kinase 1; Humans; Mice; Night Blindness; Phosphorylation; Protein Kinases; Retinal Rod Photoreceptor Cells; Rhodopsin; Vision, Ocular

Rhodopsin, the visual pigment of rod photoreceptors cells, is a member of the large family of G protein-coupled receptors. Rhodopsin is composed of two parts: a polypeptide chain called opsin and an 11-cis-retinal chromophore covalently bound to the protein by means of a protonated Schiff base linkage to Lys296 located in the seventh transmembrane segment of the protein. Several mutations have been described that constitutively activate the apoprotein opsin. These mutations appear to activate the protein by a common mechanism of action. They disrupt a salt-bridge between Lys296 and the couterion Glu113 that helps constrain the protein to an inactive conformation. Four of the mutations have been shown to cause two different diseases of the retina, retinitis pigmentosa and congenital night blindness. Recently, several other human diseases have been shown to be caused by constitutively activating mutations of G protein-coupled receptors.

Topics: GTP-Binding Proteins; Humans; Models, Molecular; Mutagenesis, Site-Directed; Night Blindness; Photochemistry; Protein Conformation; Retinitis Pigmentosa; Rhodopsin; Schiff Bases; Structure-Activity Relationship

Recent molecular genetic studies show how changes in the protein component of a visual pigment alters its absorbance; they also explain the abnormal colour vision of one of the great pioneers of visual science.

Topics: Animals; Cercopithecidae; Chemistry; Chromosomes, Human, Pair 7; Color Perception; Color Vision Defects; England; History, 18th Century; History, 19th Century; Humans; Mutation; Night Blindness; Protein Conformation; Retinal Cone Photoreceptor Cells; Retinaldehyde; Rhodopsin; Rod Opsins; Sequence Homology, Nucleic Acid; X Chromosome

The diagnostic features and future research directions of retinitis pigmentosa were documented in this update and review of the subject. An extensive and current bibliography is provided.

Topics: Cell Survival; Electroretinography; Genetic Linkage; Humans; Night Blindness; Ophthalmoscopy; Retinitis Pigmentosa; Rhodopsin; Visual Fields; X Chromosome

Rhodopsin is the G protein-coupled receptor in rod photoreceptor cells that initiates vision upon photon capture. The light receptor is normally locked in an inactive state in the dark by the covalently bound inverse agonist 11-cis retinal. Mutations can render the receptor active even in the absence of light. This constitutive activity can desensitize rod photoreceptor cells and lead to night blindness. A G90D mutation in rhodopsin causes the receptor to be constitutively active and leads to congenital stationary night blindness, which is generally thought to be devoid of retinal degeneration. The constitutively active species responsible for the night blindness phenotype is unclear. Moreover, the classification as a stationary disease devoid of retinal degeneration is also misleading. A transgenic mouse model for congenital stationary night blindness that expresses the G90D rhodopsin mutant was examined to better understand the origin of constitutive activity and the potential for retinal degeneration. Heterozygous mice for the G90D mutation did not exhibit retinal degeneration whereas homozygous mice exhibited progressive retinal degeneration. Only a modest reversal of retinal degeneration was observed when transducin signaling was eliminated genetically, indicating that some of the retinal degeneration occurred in a transducin-independent manner. Biochemical studies on purified rhodopsin from mice indicated that multiple species can potentially contribute to the constitutive activity causing night blindness.

Topics: Animals; Heterozygote; Homozygote; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Mutation; Night Blindness; Retinal Degeneration; Retinal Rod Photoreceptor Cells; Rhodopsin; Transducin

Rhodopsin is the photosensitive protein, which binds to 11-cis-retinal as its chromophore. In the dark, rhodopsin exists as a stable complex between the opsin moiety and 11-cis-retinal. The absorption of a light photon converts 11-cis-retinal to all-trans-retinal and initiates our vision. As a result, the increase in the rate of dark activation of rhodopsin reduces its photosensitivity resulting in night blindness. The mutations, G90D and T94I are night blindness-causing mutations that exhibit completely different physicochemical characteristics associated with the dark activation of rhodopsin, such as a high rate of thermal isomerization of 11-cis-retinal and a slow pigment regeneration. To elucidate the molecular mechanism by which G90D and T94I mutations affect rhodopsin dark activation and regeneration, we performed light-induced difference FTIR spectroscopy on dark and primary photo-intermediate states of G90D and T94I mutants. The FTIR spectra clearly show that both charged G90D and hydrophobic T94I mutants alter the H-bond network at the Schiff base region of the chromophore, which weakens the electrostatic interaction with Glu113 counterion. Our results further show an altered water-mediated H-bond network around the central transmembrane region of mutant rhodopsin, which is reminiscent of the active Meta-II state. This altered water-mediated H-bond network may cause thermal isomerization of the chromophore and facilitate rhodopsin dark activation.

Topics: Animals; Cattle; Hydrogen Bonding; Isomerism; Models, Molecular; Night Blindness; Point Mutation; Protein Conformation; Retinaldehyde; Rhodopsin

For night blindness, a detailed structural exploration of the interactions among G-protein receptor rhodopsin, transducin and arrestin was performed. Rhodopsin is responsible for dim light vision while a point mutation (G90→D90) results in an adverse change in its photo-transduction. The validated 3D models of the three proteins were utilized, and upon mutation and interactions, rhodopsin attained higher stability (evaluated through thermodynamic energy calculations, electrostatic surface potential and solvent accessible area), thereby participating strongly with transducin. Conformational switches in mutated rhodopsin also depicted a firm conformation with few 3

Topics: Amino Acid Substitution; Aspartic Acid; Crystallography, X-Ray; Dark Adaptation; DNA Mutational Analysis; Glycine; Humans; Models, Molecular; Night Blindness; Point Mutation; Protein Binding; Protein Interaction Domains and Motifs; Protein Interaction Maps; Protein Structure, Secondary; Rhodopsin; Signal Transduction; Structure-Activity Relationship

The G90D mutation in the rhodopsin gene leads to autosomal dominant congenital stationary night blindness (CSNB) in patients. This occurs because the G90D mutant protein cannot efficiently bind chromophore and is constitutively active. To combat this mutation, we designed and characterized two different hammerhead ribozymes to cleave G90D transcript. In vitro testing showed that the G90D1 ribozyme efficiently and specifically cleaved the mutant transcript while G90D2 cleaved both WT and mutant transcript. AAV-mediated delivery of G90D1 under the control of the mouse opsin promoter (MOP500) to G90D transgenic eyes showed that the ribozyme partially retarded the functional degeneration (as measured by electroretinography [ERG]) associated with this mutation. These results suggest that with additional optimization, ribozymes may be a useful part of the gene therapy knockdown strategy for dominant retinal disease.

Topics: Animals; Biocatalysis; Dependovirus; Electroretinography; Eye Diseases, Hereditary; Genetic Diseases, X-Linked; Genetic Therapy; Genetic Vectors; Humans; Mice, Transgenic; Mutant Proteins; Mutation; Myopia; Night Blindness; Rhodopsin; RNA; RNA, Catalytic; Substrate Specificity; Transcription, Genetic

Congenital stationary night blindness (CSNB) is an inherited and non-progressive retinal dysfunction. Here, we present the crystal structure of CSNB-causing T94I

Topics: Binding Sites; Catalytic Domain; Darkness; Eye Diseases, Hereditary; Genetic Association Studies; Genetic Diseases, X-Linked; Humans; Models, Biological; Models, Molecular; Mutation; Myopia; Night Blindness; Protein Binding; Protein Conformation; Protein Stability; Rhodopsin; Schiff Bases; Structure-Activity Relationship; Thermodynamics

The diagnoses of retinitis pigmentosa (RP) and stationary night blindness (CSNB) are two distinct clinical entities belonging to a group of clinically and genetically heterogeneous retinal diseases. The current study focused on the identification of causative mutations in the RP-affected index patient and in several members of the same family that reported a phenotype resembling CSNB. Ophthalmological examinations of the index patient confirmed a typical form of RP. In contrast, clinical characterizations and ERGs of another affected family member showed the Riggs-type CSNB lacking signs of RP. Applying whole exome sequencing we detected the non-synonymous substitution c.337G > A, p.E113 K in the rhodopsin (RHO) gene. The mutation co-segregated with the diseases. The identification of the pathogenic variant p.E113 K is the first description of a naturally-occurring mutation in the Schiff base counterion of RHO in human patients. The heterozygous mutation c.337G > A in exon 1 was confirmed in the index patient as well as in five CSNB-affected relatives. This pathogenic sequence change was excluded in a healthy family member and in 199 ethnically matched controls. Our findings suggest that a mutation in the biochemically well-characterized counterion p.E113 in RHO can be associated with RP or Riggs-type CSNB, even within the same family.

Topics: Adult; Aged, 80 and over; Amino Acid Sequence; Amino Acid Substitution; Case-Control Studies; DNA Mutational Analysis; Female; Heterozygote; Humans; Male; Middle Aged; Mutation, Missense; Night Blindness; Pedigree; Phenotype; Retinitis Pigmentosa; Rhodopsin; Schiff Bases; Sequence Analysis, DNA

We present active-state structures of the G protein-coupled receptor (GPCRs) rhodopsin carrying the disease-causing mutation G90D. Mutations of G90 cause either retinitis pigmentosa (RP) or congenital stationary night blindness (CSNB), a milder, non-progressive form of RP. Our analysis shows that the CSNB-causing G90D mutation introduces a salt bridge with K296. The mutant thus interferes with the E113Q-K296 activation switch and the covalent binding of the inverse agonist 11-cis-retinal, two interactions that are crucial for the deactivation of rhodopsin. Other mutations, including G90V causing RP, cannot promote similar interactions. We discuss our findings in context of a model in which CSNB is caused by constitutive activation of the visual signalling cascade.

Topics: Arrestin; Crystallography, X-Ray; Eye Diseases, Hereditary; Genetic Diseases, X-Linked; HEK293 Cells; Humans; Models, Molecular; Mutation, Missense; Myopia; Night Blindness; Protein Binding; Protein Stability; Protein Structure, Secondary; Protein Structure, Tertiary; Rhodopsin; Schiff Bases; Structural Homology, Protein; Transition Temperature

The effects of activating mutations associated with night blindness on the stoichiometry of rhodopsin interactions with G protein-coupled receptor kinase 1 (GRK1) and arrestin-1 have not been reported. Here we show that the monomeric form of WT rhodopsin and its constitutively active mutants M257Y, G90D, and T94I, reconstituted into HDL particles are effectively phosphorylated by GRK1, as well as two more ubiquitously expressed subtypes, GRK2 and GRK5. All versions of arrestin-1 tested (WT, pre-activated, and constitutively monomeric mutants) bind to monomeric rhodopsin and show the same selectivity for different functional forms of rhodopsin as in native disc membranes. Rhodopsin phosphorylation by GRK1 and GRK2 promotes arrestin-1 binding to a comparable extent, whereas similar phosphorylation by GRK5 is less effective, suggesting that not all phosphorylation sites on rhodopsin are equivalent in promoting arrestin-1 binding. The binding of WT arrestin-1 to phospho-opsin is comparable to the binding to its preferred target, P-Rh*, suggesting that in photoreceptors arrestin-1 only dissociates after opsin regeneration with 11-cis-retinal, which converts phospho-opsin into inactive phospho-rhodopsin that has lower affinity for arrestin-1. Reduced binding of arrestin-1 to the phospho-opsin form of G90D mutant likely contributes to night blindness caused by this mutation in humans.

Topics: Animals; Arrestin; Cattle; Cholesterol, HDL; G-Protein-Coupled Receptor Kinase 1; Gene Expression Regulation; Isoenzymes; Mutation; Night Blindness; Opsins; Phosphoproteins; Phosphorylation; Protein Binding; Protein Isoforms; Protein Multimerization; Retinal Rod Photoreceptor Cells; Rhodopsin; Signal Transduction

Bothnia dystrophy is a variant of recessive retinitis punctata albescens (RPA) and is caused by a homozygous R234W mutation in the RLBP1 gene. We report the clinical features of a Japanese patient with the homozygous R234W mutation in the RLBP1 gene.. An affected woman with RPA has been examined clinically for 25 years. Her DNA was obtained with informed consent, and the exons and surrounding areas of RDH5, rhodopsin, and RLBP1 were amplified by PCR and directly sequenced.. Our patient was first examined in our hospital in 1986 when she was 6 years old. Ophthalmoscopy showed numerous small white dots in the posterior pole of both eyes. Although the a- and b-waves of the single flash ERGs were severely reduced after a standard 30 min of dark-adaptation, the amplitudes of both waves increased markedly after 24 hr of dark-adaptation. The visual disturbances and visual field scotomas became more evident in her twenties, and her BCVAs were 0.2 OD and 0.5 OS when she was 31 years old in 2010. Fundus examinations showed macular degeneration in both eyes. A homozygous R234W mutation was detected in RLBP1, and no mutations were detected in RDH5 and rhodopsin.. The clinical characteristics of a Japanese patient with a homozygous R234W mutation in RLBP1 are very similar to that of Swedish patients with Bothnia dystrophy. The origin of the Japanese R234W mutation is probably not the same as that of the Swedish patients, but more likely due to the high incidence of C to T transitions.

Topics: Adult; Alcohol Oxidoreductases; Asian People; Carrier Proteins; Dark Adaptation; DNA Mutational Analysis; Electroretinography; Exons; Female; Fluorescein Angiography; Humans; Japan; Mutation, Missense; Night Blindness; Polymerase Chain Reaction; Retinal Dystrophies; Rhodopsin; Tomography, Optical Coherence; Visual Acuity; Visual Fields

To detect genetic mutations associated with autosomal dominant congenital stationary night blindness (ADCSNB) in a family from Henan province.. Genomic DNA was extracted from peripheral blood samples of 14 family members. Based on 3 genes reported previously, PCR primers were designed and corresponding exons containing the mutation sites were amplified with PCR. PCR products were purified and directly sequenced.. A c.281C>T heterozygous missense mutation was detected in RHO gene in all of the patients. This mutation can cause a change of the protein structure (p.Thr94Ile). The same mutation was not detected in normal individuals from the family and 50 normal controls.. A c.281C>T mutation in RHO gene is responsible for the onset of ADCSNB in this Chinese family and results in symptoms of night blindness.

Topics: Adult; Amino Acid Sequence; China; DNA Mutational Analysis; Eye Diseases, Hereditary; Female; Genetic Diseases, X-Linked; Genetic Predisposition to Disease; Humans; Male; Molecular Sequence Data; Mutation, Missense; Myopia; Night Blindness; Rhodopsin; Sequence Alignment

Several point mutations in rhodopsin cause retinal diseases including congenital stationary night blindness and retinitis pigmentosa. The mechanism by which a single amino acid residue substitution leads to dysfunction is poorly understood at the molecular level. A G90D point mutation in rhodopsin causes constitutive activity and leads to congenital stationary night blindness. It is unclear which perturbations the mutation introduces and how they can cause the receptor to be constitutively active. To reveal insight into these mechanisms, we characterized the perturbations introduced into dark state G90D rhodopsin from a transgenic mouse model expressing exclusively the mutant rhodopsin in rod photoreceptor cells. UV-visible absorbance spectroscopy revealed hydroxylamine accessibility to the chromophore-binding pocket of dark state G90D rhodopsin, which is not detected in dark state wild-type rhodopsin but is detected in light-activated wild-type rhodopsin. Single-molecule force spectroscopy suggested that the structural changes introduced by the mutation are small. Dynamic single-molecule force spectroscopy revealed that, compared with dark state wild-type rhodopsin, the G90D mutation decreased energetic stability and increased mechanical rigidity of most structural regions in the dark state mutant receptor. The observed structural, energetic, and mechanical changes in dark state G90D rhodopsin provide insights into the nature of perturbations caused by a pathological point mutation. Moreover, these changed properties observed for dark state G90D rhodopsin are consistent with properties expected for an active state.

Topics: Amino Acid Sequence; Animals; Eye Diseases, Hereditary; Genetic Diseases, X-Linked; Mice; Mice, Transgenic; Microscopy, Atomic Force; Molecular Sequence Data; Mutation; Myopia; Night Blindness; Point Mutation; Protein Structure, Secondary; Protein Structure, Tertiary; Receptors, G-Protein-Coupled; Rhodopsin; Rod Cell Outer Segment; Spectrophotometry; Stress, Mechanical; Thermodynamics; Ultraviolet Rays

Retinitis pigmentosa (RP) refers to a heterogeneous group of inherited diseases that result in progressive retinal degeneration, characterized by visual field constriction and night blindness. A total of 103 mutations in rhodopsin are linked to RP to date, and the phenotypes range from severe to asymptomatic. To study the relation between phenotype and rhodopsin stability in disease mutants, we used a structure-based approach. For 12 of the mutants located at the protein-lipid interphase, we used the von Heijne water-membrane transfer scale, and we find that 9 of the mutations could affect membrane insertion. For 91 mutants, we used the protein design algorithm FoldX. The 3 asymptomatic mutations had no significant reduced stability, 2 were unsuitable for FoldX analysis since the structure was incorrect in this region, 63 mutations had a significant change in protein stability (>1.6 kcal/mol), and 23 mutations had energy change values under the prediction error threshold (<1.6 kcal/mol). Out of these 23, the disease-causing effect could be explained by the involvement in other functions (e.g., glycosylation motifs, the interface with arrestin and transducin, and the cilia-binding motif) for 19 mutants. The remaining 4 mutants were probably incorrectly associated with RP or have functionalities not discovered yet. For destabilizing mutations where clinical data were available, we found a highly significant correlation between FoldX energy changes and the average age of night blindness and between FoldX energy changes and daytime vision loss onset. Our detailed structural, functional, and energetic analysis provides a complete picture of the rhodopsin mutations and can guide mutation-specific therapies.

Topics: Adolescent; Adult; Aged; Aged, 80 and over; Amino Acid Sequence; Child; Child, Preschool; Humans; Infant; Infant, Newborn; Middle Aged; Models, Molecular; Molecular Dynamics Simulation; Molecular Sequence Data; Mutation, Missense; Night Blindness; Protein Folding; Retinitis Pigmentosa; Rhodopsin; Young Adult

Two different mutations at Gly-90 in the second transmembrane helix of the photoreceptor protein rhodopsin have been proposed to lead to different phenotypes. G90D has been classically associated with congenital night blindness, whereas the newly reported G90V substitution was linked to a retinitis pigmentosa phenotype. Here, we used Val/Asp replacements of the native Gly at position 90 to unravel the structure/function divergences caused by these mutations and the potential molecular mechanisms of inherited retinal disease. The G90V and G90D mutants have a similar conformation around the Schiff base linkage region in the dark state and same regeneration kinetics with 11-cis-retinal, but G90V has dramatically reduced thermal stability when compared with the G90D mutant rhodopsin. The G90V mutant also shows, like G90D, an altered photobleaching pattern and capacity to activate Gt in the opsin state. Furthermore, the regeneration of the G90V mutant with 9-cis-retinal was improved, achieving the same A(280)/A(500) as wild type isorhodopsin. Hydroxylamine resistance was also recovered, indicating a compact structure around the Schiff base linkage, and the thermal stability was substantially improved when compared with the 11-cis-regenerated mutant. These results support the role of thermal instability and/or abnormal photoproduct formation in eliciting a retinitis pigmentosa phenotype. The improved stability and more compact structure of the G90V mutant when it was regenerated with 9-cis-retinal brings about the possibility that this isomer or other modified retinoid analogues might be used in potential treatment strategies for mutants showing the same structural features.

Topics: Amino Acid Substitution; Animals; Cattle; Cell Line, Tumor; COS Cells; Diterpenes; Eye Diseases, Hereditary; Genetic Diseases, X-Linked; Humans; Mutation, Missense; Myopia; Night Blindness; Protein Stability; Protein Structure, Tertiary; Retinaldehyde; Retinitis Pigmentosa; Rhodopsin; Structure-Activity Relationship

Congenital stationary night blindness (CSNB) is a clinically and genetically heterogeneous retinal disease. Although electroretinographic (ERG) measurements can discriminate clinical subgroups, the identification of the underlying genetic defects has been complicated for CSNB because of genetic heterogeneity, the uncertainty about the mode of inheritance, and time-consuming and costly mutation scanning and direct sequencing approaches.. To overcome these challenges and to generate a time- and cost-efficient mutation screening tool, the authors developed a CSNB genotyping microarray with arrayed primer extension (APEX) technology. To cover as many mutations as possible, a comprehensive literature search was performed, and DNA samples from a cohort of patients with CSNB were first sequenced directly in known CSNB genes. Subsequently, oligonucleotides were designed representing 126 sequence variations in RHO, CABP4, CACNA1F, CACNA2D4, GNAT1, GRM6, NYX, PDE6B, and SAG and spotted on the chip.. Direct sequencing of genes known to be associated with CSNB in the study cohort revealed 21 mutations (12 novel and 9 previously reported). The resultant microarray containing oligonucleotides, which allow to detect 126 known and novel mutations, was 100% effective in determining the expected sequence changes in all known samples assessed. In addition, investigation of 34 patients with CSNB who were previously not genotyped revealed sequence variants in 18%, of which 15% are thought to be disease-causing mutations.. This relatively inexpensive first-pass genetic testing device for patients with a diagnosis of CSNB will improve molecular diagnostics and genetic counseling of patients and their families and gives the opportunity to analyze whether, for example, more progressive disorders such as cone or cone-rod dystrophies underlie the same gene defects.

Topics: Adolescent; Calcium Channels, L-Type; Calcium-Binding Proteins; Child; Cyclic Nucleotide Phosphodiesterases, Type 6; DNA Mutational Analysis; Eye Proteins; Female; Gene Expression Profiling; Genotype; Heterotrimeric GTP-Binding Proteins; Humans; Male; Mutation; Night Blindness; Oligonucleotide Array Sequence Analysis; Pedigree; Polymerase Chain Reaction; Proteoglycans; Receptors, Metabotropic Glutamate; Retinal Diseases; Rhodopsin; Transducin

To define the retinal pathology in an 88-year-old male affected with Goldmann-Favre syndrome with a 2 bp 5' A>C splice site mutation in the NR2E3 gene.. Retinal tissue from the macula and periphery was processed for immunohistochemistry. Perimacular retina was processed for transmission electron microscopy. Cryosections were studied by indirect immunofluorescence, using well-characterized antibodies to rhodopsin, cone cytoplasm, and cone opsins. The affected donor eye was compared to a postmortem matched normal eye.. The retina was highly disorganized without laminar organization. The RPE was discontinuous in some perimacular regions. Large (>1 mm) spherical electrondense melanosomes were observed in the RPE and choroid by TEM. Rods were virtually absent in the affected retina. Cones were present in the macula, but were mostly absent from the retinal periphery. In addition, cone rosettes were observed in the perimacular area. Both red/green and blue cone opsins were distributed along the entire cellular expanse of the cone photoreceptors in the affected eye, but were restricted to the cone outer segments in the control retina.. The histological data obtained from the retina of an elderly male patient with Goldmann-Favre syndrome showed an absence of rods and abnormal distribution of red/green and blue cone opsins.

Topics: Aged; Aged, 80 and over; Arrestin; Fluorescent Antibody Technique, Indirect; Humans; Male; Night Blindness; Opsins; Orphan Nuclear Receptors; Retina; Retinal Degeneration; Retinal Pigment Epithelium; Rhodopsin; Syndrome

The G90D rhodopsin mutation is known to produce congenital night blindness in humans. This mutation produces a similar condition in mice, because rods of animals heterozygous (D+) or homozygous (D+/+) for this mutation have decreased dark current and sensitivity, reduced Ca(2+), and accelerated values of tau(REC) and tau(D), similar to light-adapted wild-type (WT) rods. Our experiments indicate that G90D pigment activates the cascade, producing an equivalent background light of approximately 130 Rh* rod(-1) for D+ and 890 Rh* rod(-1) for D+/+. The active species of the G90D pigment could be unregenerated G90D opsin or G90D rhodopsin, either spontaneously activated (as Rh*) or in some other form. Addition of 11-cis-retinal in lipid vesicles, which produces regeneration of both WT and G90D opsin in intact rods and ROS membranes, had no effect on the waveform or sensitivity of dark-adapted G90D responses, indicating that the active species is not G90D opsin. The noise spectra of dark-adapted G90D and WT rods are similar, and the G90D noise variance is much less than of a WT rod exposed to background light of about the same intensity as the G90D equivalent light, indicating that Rh* is not the active species. We hypothesize that G90D rhodopsin undergoes spontaneous changes in molecular conformation which activate the transduction cascade with low gain. Our experiments provide the first indication that a mutant form of the rhodopsin molecule bound to its 11-cis-chromophore can stimulate the visual cascade spontaneously at a rate large enough to produce visual dysfunction.

Topics: Animals; Aspartic Acid; Calcium; Carrier Proteins; cis-trans-Isomerases; Dark Adaptation; Disease Models, Animal; Dose-Response Relationship, Radiation; Eye Proteins; Glycine; Kinetics; Light Signal Transduction; Membrane Potentials; Mice; Mice, Transgenic; Mutation; Night Blindness; Opsins; Photic Stimulation; Retinal Rod Photoreceptor Cells; Retinaldehyde; Rhodopsin; Spectrum Analysis; Time Factors

Mutations in RHO, PDE6B, and GNAT1 can lead to autosomal dominant congenital stationary night blindness (adCSNB). The study was conducted to identify the genetic defect in a large Swiss family affected with adCSNB and to investigate the pathogenic mechanism of the mutation.. Two affected cousins of a large Swiss family were examined clinically by standard methods: funduscopy, EOG, ERG, and dark adaptometry. Twelve family members were screened for mutations in RHO. The ability of mutant rhodopsin to activate transducin constitutively was monitored by measuring the catalytic exchange of bound GDP for radiolabeled [(35)S]GTPgammaS in transducin.. A novel mutation was identified in RHO (c.884C>T, p.Ala295Val) in patients with adCSNB. They had full vision under photopic conditions, showed no fundus abnormalities, revealed EOG results in the normal range, but presented night blindness with an altered scotopic ERG. In the presence of 11-cis retinal, the mutant rhodopsin is inactive, similar to wild-type, responding only when exposed to light. However, in the absence of 11-cis-retinal, unlike wild-type opsin, the mutant opsin constitutively activates transducin.. The study adds a fourth rhodopsin mutation associated with CSNB. Although the phenotype of autosomal dominant CSNB may vary slightly in patients showing mutations in RHO, PDE6B, or GNAT1, the disease course seems to be stationary with only scotopic vision being affected. The data indicate that the mutant opsin activates transducin constitutively, which is a consistent and common feature of all four CSNB-associated rhodopsin mutations reported to date.

Topics: Acclimatization; Cyclic Nucleotide Phosphodiesterases, Type 6; Darkness; DNA Mutational Analysis; Electrooculography; Electroretinography; Eye Proteins; Female; Genes, Dominant; Heterotrimeric GTP-Binding Proteins; Humans; Male; Mutation; Night Blindness; Pedigree; Rho Factor; Rhodopsin; Transducin; Visual Fields

Identification of a novel rhodopsin mutation in a family with retinitis pigmentosa and comparison of the clinical phenotype to a known mutation at the same amino acid position.. Screening for mutations in rhodopsin was performed in 78 patients with retinitis pigmentosa. All exons and flanking intronic regions were amplified by PCR, sequenced, and compared to the reference sequence derived from the National Center for Biotechnology Information (NCBI, Bethesda, MD) database. Patients were characterized clinically according to the results of best corrected visual acuity testing (BCVA), slit lamp examination (SLE), funduscopy, Goldmann perimetry (GP), dark adaptometry (DA), and electroretinography (ERG). Structural analyses of the rhodopsin protein were performed with the Swiss-Pdb Viewer program available on-line (http://www.expasy.org.spdvbv/ provided in the public domain by Swiss Institute of Bioinformatics, Geneva, Switzerland).. A novel rhodopsin mutation (Gly90Val) was identified in a Swiss family of three generations. The pedigree indicated autosomal dominant inheritance. No additional mutation was found in this family in other autosomal dominant genes. The BCVA of affected family members ranged from 20/25 to 20/20. Fundus examination showed fine pigment mottling in patients of the third generation and well-defined bone spicules in patients of the second generation. GP showed concentric constriction. DA demonstrated monophasic cone adaptation only. ERG revealed severely reduced rod and cone signals. The clinical picture is compatible with retinitis pigmentosa. A previously reported amino acid substitution at the same position in rhodopsin leads to a phenotype resembling night blindness in mutation carriers, whereas patients reported in the current study showed the classic retinitis pigmentosa phenotype. The effect of different amino acid substitutions on the three-dimensional structure of rhodopsin was analyzed by homology modeling. Distinct distortions of position 90 (shifts in amino acids 112 and 113) and additional hydrogen bonds were found.. Different amino acid substitutions at position 90 of rhodopsin can lead to night blindness or retinitis pigmentosa. The data suggest that the property of the substituted amino acid distinguishes between the phenotypes.

Topics: Adult; Amino Acid Substitution; DNA Mutational Analysis; Electroretinography; Female; Genes, Dominant; Humans; Male; Middle Aged; Mutation, Missense; Night Blindness; Pedigree; Phenotype; Polymerase Chain Reaction; Retina; Retinitis Pigmentosa; Rhodopsin; Visual Acuity; Visual Field Tests; Visual Fields

We compare the known retinitis pigmentosa (RP) mutations in rhodopsin with mutational data obtained for the complement factor 5a receptor (C5aR), a member of the rhodopsin-like family of G protein-coupled receptors (GPCRs). We have performed genetic analyses that define residues that are required for C5aR folding and function. The cognate residues in rhodopsin are not preferentially mutated in RP, suggesting that the predominant molecular defect in RP involves more than simple misfolding or inactivation. Energy calculations are performed to elucidate the structural effects of the RP mutations. Many of these mutations specifically disrupt the environment of the retinal prosthetic group of rhodopsin, and these do not correspond to essential residues in C5aR. This may be because a retinal group is present in rhodopsin but not in C5aR. Another subset of RP mutations is more generally important for receptor structure, and these mutations correlate with essential residues of C5aR.

Topics: Amino Acid Sequence; Animals; Cattle; Humans; Models, Molecular; Molecular Sequence Data; Night Blindness; Protein Structure, Quaternary; Receptor, Anaphylatoxin C5a; Retinitis Pigmentosa; Rhodopsin; Sequence Alignment; Structure-Activity Relationship; Vision, Ocular

We report that visual arrestin can regulate retinal release and late photoproduct formation in rhodopsin. Our experiments, which employ a fluorescently labeled arrestin and rhodopsin solubilized in detergent/phospholipid micelles, indicate that arrestin can trap a population of retinal in the binding pocket with an absorbance characteristic of Meta II with the retinal Schiff-base intact. Furthermore, arrestin can convert Metarhodopsin III (formed either by thermal decay or blue-light irradiation) to a Meta II-like absorbing species. Together, our results suggest arrestin may be able to play a more complex role in the rod cell besides simply quenching transducin activity. This possibility may help explain why arrestin deficiency leads to problems like stationary night blindness (Oguchi disease) and retinal degeneration.

Topics: Animals; Arrestin; Dark Adaptation; Micelles; Night Blindness; Protein Binding; Recombinant Proteins; Retinal Rod Photoreceptor Cells; Retinaldehyde; Rhodopsin; Schiff Bases; Spectrophotometry, Ultraviolet; Transducin; Vision, Ocular

A subset of genetic mutations in photoreceptor-specific genes results in abnormally prolonged activation of transducin-mediated photosignaling in rod cells. In humans and animal models, these mutations cause visual dysfunctions ranging from a mild stationary night blindness to severe, early-onset retinal degeneration. There are mechanistic differences between mutations causing night blindness and those causing retinal degeneration. Here, we hypothesize that mutations causing continuous activation of the visual cascade as the result, for example, of the inability of the photoreceptor to regenerate rhodopsin, lead to retinal degeneration; those mutations that can terminate signaling, even if only partially and intermittently, slow the rate of degeneration sufficiently to give rise to stationary night blindness. Furthermore, we hypothesize that a prolonged decrease in intracellular calcium concentration resulting from persistent activation is responsible for triggering apoptotic rod-cell death.

Topics: Animals; Apoptosis; Calcium; Humans; Models, Biological; Mutation; Night Blindness; Photoreceptor Cells; Retinal Degeneration; Retinal Rod Photoreceptor Cells; Rhodopsin; Rod Opsins; Signal Transduction; Transducin

Several mutations in the opsin gene have been associated with congenital stationary night blindness, considered to be a relatively nonprogressive disorder. In the present study, we examined the structural and functional changes induced by one of these mutations, i.e., substitution of aspartic acid for glycine at position 90 (G90D). Transgenic mice were created in which the ratio of transgenic opsin transcript to endogenous was 0.5:1, 1.7:1, or 2.5:1 and were studied via light and electron microscopy, immunocytochemistry, electroretinography (ERG), and spectrophotometry. Retinas with transgenic opsin levels equivalent to one endogenous allele (G0.5) appeared normal for a period of about 3-4 months, but at later ages there were disorganized, shortened rod outer segments (ROS), and a loss of photoreceptor nuclei. Higher levels of G90D opsin expression produced earlier signs of retinal degeneration and more severe disruption of photoreceptor morphology. Despite these adverse effects, the mutation had a positive effect on the retinas of rhodopsin knockout (R-/-) mice, whose visual cells fail to form ROS and rapidly degenerate. Incorporation of the transgene in the null background (G+/-/R-/- or G+/+/R-/-) led to the development of ROS containing G90D opsin and prolonged survival of photoreceptors. Absorbance spectra measured both in vitro and in situ showed a significant reduction of more than 90% in the amount of light-sensitive pigment in the retinas of G+/+/R-/- mice, and ERG recordings revealed a >1 log unit loss in sensitivity. However, the histological appearances of the retinas of these mice show no significant loss of photoreceptors and little change in the lengths of their outer segments. These findings suggest that much of the ERG sensitivity loss derives from the reduced quantal absorption that results from a failure of G90D opsin to bind to its chromophore and form a normal complement of light-sensitive visual pigment.

Topics: Animals; Blotting, Northern; Blotting, Western; Disease Models, Animal; Electroretinography; Immunohistochemistry; Mice; Mice, Knockout; Mice, Transgenic; Microscopy, Electron; Nerve Degeneration; Night Blindness; Point Mutation; Retina; Rhodopsin; Rod Opsins; Spectrophotometry; Transgenes

Naturally occurring point mutations in the opsin gene cause the retinal diseases retinitis pigmentosa and congenital night blindness. Although these diseases involve similar mutations in very close locations in rhodopsin, their progression is very different, with retinitis pigmentosa being severe and causing retinal degeneration. We report on the expression and characterization of the recently found T94I mutation associated with congenital night blindness, in the second transmembrane helix or rhodopsin, and mutations at the same site. T94I mutant rhodopsin folded properly and was able to bind 11-cis-retinal to form chromophore, but it showed a blue-shifted visible band at 478 nm and reduced molar extinction coefficient. Furthermore, T94I showed dramatically reduced thermal stability, extremely long lived metarhodopsin II intermediate, and highly increased reactivity toward hydroxylamine in the dark, when compared with wild type rhodopsin. The results are consistent with the location of Thr-94 in close proximity to Glu-113 counterion in the vicinity of the Schiff base linkage and suggest a role for this residue in maintaining the correct dark inactive conformation of the receptor. The reported results, together with previously published data on the other two known congenital night blindness mutants, suggest that the molecular mechanism underlying this disease may not be structural misfolding, as proposed for retinitis pigmentosa mutants, but abnormal functioning of the receptor by decreased thermal stability and/or constitutive activity.

Topics: Amino Acid Sequence; Amino Acid Substitution; Base Sequence; Darkness; DNA Primers; Humans; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutation, Missense; Night Blindness; Protein Conformation; Protein Structure, Secondary; Rhodopsin; Spectrophotometry; Thermodynamics

In an examination of the effect of three rhodopsin night blindness mutations on the rate of association of 11-cis-retinal with opsin, one of the mutations (G90D) was found to slow the rate of reaction by more than 80-fold. This effect does not appear to be general to night blindness mutations as the two other mutants (A292E and T94I) were not found to bind retinal with slowed kinetics. However, T94D was similar to G90D in that the rate of retinal binding was dramatically slowed. Gly90 and Thr94 are both located in the active site of the protein close to the Schiff base counterion Glu113. Thus, the slow kinetics of Schiff base formation appear to correlate with the introduction of a negative charge close to the Schiff base counterion, suggesting a possible role for Glu113 as a catalytic base in this reaction. Consistent with this model, the E113Q mutant was also found to bind retinal more slowly than the wild type.

Topics: Alanine; Amino Acid Sequence; Animals; Aspartic Acid; Glutamic Acid; Glutamine; Glycine; Humans; Molecular Sequence Data; Mutagenesis, Insertional; Night Blindness; Protein Binding; Protein Denaturation; Retinaldehyde; Rhodopsin; Schiff Bases; Spectrophotometry, Ultraviolet; Threonine

The Thr94 --> Ile mutation in the second transmembrane segment of rhodopsin has been reported to be associated with a congenital night blindness phenotype in a large Irish pedigree. Previously, two other known rhodopsin mutants that cause congenital night blindness, A292E and G90D, have been shown in vitro to constitutively activate the G protein transducin in the absence of a chromophore. The proposed mechanism of constitutive activation of these two mutants is an electrostatic disruption of the active site salt bridge between Glu113 and Lys296 that contributes to stabilization of the protein in the inactive state. Here, the T94I rhodopsin mutant is characterized and compared to the two other known rhodopsin night blindness mutants. The T94I mutant opsin is shown also to constitutively activate transducin. The T94I mutant pigment (with a bound 11-cis-retinal chromophore), like the other known rhodopsin night blindness mutants, is not active in the dark and has wild-type activity upon exposure to light. Similar to the Gly90 --> Asp substitution, position 94 is close enough to the Schiff base nitrogen that an Asp at this position can functionally substitute for the Glu113 counterion. However, in contrast to the other night blindness mutants, the T94I MII intermediate decays with a half-life that is approximately 8-fold slower than in the wild-type MII intermediate. Thus, the one phenotype shared by all congenital night blindness mutants that is different from the wild-type protein is constitutive activation of the apoprotein.

Topics: Amino Acid Sequence; Animals; Cattle; COS Cells; Glutamic Acid; Glutamine; Humans; Hydrogen-Ion Concentration; Isoleucine; Kinetics; Light; Molecular Sequence Data; Mutagenesis, Insertional; Night Blindness; Rhodopsin; Schiff Bases; Threonine; Transducin; Transfection

Three different mutations of rhodopsin are known to cause autosomal dominant congenital night blindness in humans. Although the mutations have been studied for 10 years, the molecular mechanism of the disease is still a subject of controversy. We show here, using a transgenic Xenopus laevis model, that the photoreceptor cell desensitization that is a hallmark of the disease results from persistent signaling by constitutively active mutant opsins.

Topics: Animals; Animals, Genetically Modified; Disease Models, Animal; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Electrophysiology; Green Fluorescent Proteins; Humans; Luminescent Proteins; Membrane Potentials; Microscopy, Fluorescence; Mutation; Night Blindness; Phenotype; Photic Stimulation; Photoreceptor Cells; Protein Conformation; Retinaldehyde; Rhodopsin; Xenopus laevis

The natural ligand of the retinal photoreceptor rhodopsin, 11-cis-retinal, is isomerized to its all-trans configuration as a consequence of light absorption in the first step of the visual phototransduction process. Here we show, by means of difference spectroscopy and high-performance liquid chromatography analysis, that thermal denaturation of rhodopsin induces the same type of isomerization. This effect is likely due to thermally induced conformational rearrangements of amino acid residues in the retinal-binding pocket--possibly implying helical movements--and highlights the tight coupling between 11-cis-retinal and opsin. This effect could have implications in the instability and functional changes seen for certain mutations in rhodopsin associated with retinal disease, and in the stability of the different conformers induced by mutations in other G protein-coupled receptors.

Topics: Animals; Cattle; Chromatography, High Pressure Liquid; Hot Temperature; Night Blindness; Protein Denaturation; Receptors, G-Protein-Coupled; Retinal Diseases; Retinaldehyde; Rhodopsin; Spectrum Analysis; Stereoisomerism

To detect rhodopsin (RHO) mutation in Chinese families with autosomal dominant retinitis pigmentosa (ADRP) and study on the association of RHO gene mutations with clinical phenotype.. Twenty-seven members from 13 Chinese families with ADRP and 30 normal subjects were recruited. The complete coding regions of the rhodopsin gene were amplified with polymerase chain reaction (PCR) and then DNA single-strand conformation polymorphism (SSCP) technique was used to screen RHO gene mutations. When a variant band was observed after the SSCP electrophoresis, the variant band was analyzed by sequencing PCR-amplified DNA. All subjects were examined clinically by slit-lamp, direct funduscopy, Goldmann kinetic perimetry, Humphrey threshold perimetry and electroretinogram.. Nine affected subjects and 2 boys (11 and 9 years old respectively) in one pedigree among 13 families were found to have three DNA single strand bands by SSCP analysis. Results of assaying sequence showed the 11 members were heterozygous for rhodopsin E341ter mutation. The codon 341 is changed from GAG to TAG, resulting in a stop codon mutation. Thirty normal controls and unaffected subjects in this family were the wild type of RHO gene. Affected individuals reported night blindness in the second decade, showed optic atrophy, vessel attenuation and a few bone spicule-like pigments in the peripheral retina. The impairment of visual acuity was relatively severe, loss of peripheral visual field was greatly considerable after 30 years of age, rod and cone ERG were not detectable in the second decade, and only slight cone response was left.. The natural history of RP in this family begins with a loss of rod function, progresses to involve the cone system, and leads eventually to a severe loss of visual function. A novel rhodopsin gene mutation E341ter is responsible for a Chinese family with ADRP.

Topics: Adult; Asian People; Codon, Terminator; DNA, Single-Stranded; Female; Genetic Predisposition to Disease; Heterozygote; Humans; Male; Middle Aged; Night Blindness; Optic Atrophy; Pedigree; Phenotype; Point Mutation; Polymerase Chain Reaction; Polymorphism, Single-Stranded Conformational; Retinitis Pigmentosa; Rhodopsin

Isotretinoin (13-cis retinoic acid) is frequently prescribed for severe acne [Peck, G. L., Olsen, T. G., Yoder, F. W., Strauss, J. S., Downing, D. T., Pandya, M., Butkus, D. & Arnaud-Battandier, J. (1979) N. Engl. J. Med. 300, 329-333] but can impair night vision [Fraunfelder, F. T., LaBraico, J. M. & Meyer, S. M. (1985) Am. J. Ophthalmol. 100, 534-537] shortly after the beginning of therapy [Shulman, S. R. (1989) Am. J. Public Health 79, 1565-1568]. As rod photoreceptors are responsible for night vision, we administered isotretinoin to rats to learn whether night blindness resulted from rod cell death or from rod functional impairment. High-dose isotretinoin was given daily for 2 months and produced systemic toxicity, but this caused no histological loss of rod photoreceptors, and rod-driven electroretinogram amplitudes were normal after prolonged dark adaptation. Additional studies showed, however, that even a single dose of isotretinoin slowed the recovery of rod signaling after exposure to an intense bleaching light, and that rhodopsin regeneration was markedly slowed. When only a single dose was given, rod function recovered to normal within several days. Rods and cones both showed slow recovery from bleach after isotretinoin in rats and in mice. HPLC analysis of ocular retinoids after isotretinoin and an intense bleach showed decreased levels of rhodopsin chromophore, 11-cis retinal, and the accumulation of the biosynthetic intermediates, 11-cis and all-trans retinyl esters. Isotretinoin was also found to protect rat photoreceptors from light-induced damage, suggesting that strategies of altering retinoid cycling may have therapeutic implications for some forms of retinal and macular degeneration.

Topics: Animals; Isotretinoin; Light; Male; Mice; Mice, Inbred C57BL; Night Blindness; Rats; Rats, Sprague-Dawley; Retinal Cone Photoreceptor Cells; Retinal Rod Photoreceptor Cells; Rhodopsin; Vision, Ocular

A dominant form of human congenital nightblindness is caused by a gly90-->asp (G90D) mutation in rhodopsin. G90D has been shown to activate the phototransduction cascade in the absence of light in vitro. Such constitutive activity of G90D rhodopsin in vivo would desensitize rod photoreceptors and lead to nightblindness. In contrast, other rhodopsin mutations typically give rise to nightblindness by causing rod cell death. Thus, the proposed desensitization without rod degeneration would be a novel mechanism for this disorder. To explore this possibility, we induced mice to express G90D opsin in their rods and then examined rod function and morphology, after first crossing the transgenic animals with rhodopsin knock-out mice to obtain appropriate levels of opsin expression. The G90D mouse opsin bound the chromophore and formed a bleachable visual pigment with lambda(max) of 492 nm that supported rod photoresponses. (G+/-, R+/-) retinas, heterozygous for both G90D and wild-type (WT) rhodopsin, possessed normal numbers of photoreceptors and had a normal rhodopsin complement but exhibited considerable loss of rod sensitivity as measured electroretinographically. The rod photoresponses were desensitized, and the response time to peak was faster than in (R+/-) animals. An equivalent desensitization resulted by exposing WT retinas to a background light producing 82 photoisomerizations rod(-1) sec(-1), suggesting that G90D rods in darkness act as if they are partially "light-adapted." Adding a second G90D allele gave (G+/+, R+/-) animals that exhibited a further increase of equivalent background light level but had no rod cell loss by 24 weeks of age. (G+/+, R-/-) retinas that express only the mutant rhodopsin develop normal rod outer segments and show minimal rod cell loss even at 1 year of age. We conclude that G90D is constitutively active in mouse rods in vivo but that it does not cause significant rod degeneration. Instead, G90D desensitizes rods by a process equivalent to light adaptation.

Topics: Adaptation, Ocular; Alleles; Amino Acid Substitution; Animals; Cell Count; Disease Models, Animal; Dose-Response Relationship, Radiation; Electroretinography; Genes, Dominant; Genotype; Heterozygote; Homozygote; Humans; Immunohistochemistry; Light; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Transgenic; Night Blindness; Retina; Retinal Rod Photoreceptor Cells; Rhodopsin

More than 100 mutations within the rhodopsin gene have been found to be responsible for some forms of retinitis pigmentosa, a progressive retinal degeneration characterized by night blindness and subsequent disturbance of day vision that may eventually result in total blindness. Congenital stationary night blindness (CSNB) is an uncommon inherited retinal dysfunction in which patients complain of night vision difficulties of a nonprogressive nature only and in which generally there is no involvement of day vision. We report the results of molecular genetic analysis of an Irish family segregating an autosomal dominant form of CSNB in which a previously unreported threonine-to-isoleucine substitution at codon 94 in the rhodopsin gene was found to segregate with the disease. Computer modeling suggests that constitutive activation of transducin by the altered rhodopsin protein may be a mechanism for disease causation in this family. Only two mutations within the rhodopsin gene have been previously reported in patients with congenital stationary night blindness, constitutive activation also having been proposed as a possible disease mechanism.

Topics: Amino Acid Substitution; Computer Simulation; Dark Adaptation; Female; Humans; Ireland; Isoleucine; Male; Middle Aged; Mutation, Missense; Night Blindness; Pedigree; Polymerase Chain Reaction; Rhodopsin; Threonine

Several ophthalmic conditions manifest a flecked retina. Developing an understanding of their clinical presentations will enable the practitioner to most appropriately manage these conditions.. A 27-year-old Middle Eastern woman manifested flecked retinas and nyctalopia. She had been given a diagnosis of retinitis punctata albescens, an inherited, progressive, night blindness; however, the medical history and clinical findings were not consistent with this disorder. Rather, they were consistent with fundus albipunctatus, an autosomal recessive, stationary, night blindness. The clinical presentation of fundus albipunctatus is characterized by discrete, white dots at the level of the retinal pigment epithelium and stable night blindness. A prolonged time for dark adaptation is required to produce normal amplitude electroretinograms in fundus albipunctatus as the result of a delay in the regeneration of rhodopsin. An electroretinogram administered after a prolonged dark adaptation time confirmed the diagnosis of stationary night blindness.. In order to ensure an accurate diagnosis for fundus albipunctatus, it is important to be aware of the clinical characteristics and appropriate electroretinogram protocol for this disorder.

Topics: Adult; Dark Adaptation; Diagnosis, Differential; Electroretinography; Eye Diseases, Hereditary; Female; Fundus Oculi; Humans; Night Blindness; Retinal Diseases; Retinal Rod Photoreceptor Cells; Rhodopsin; Syndrome

To determine whether constitutive signal flow arising from defective rhodopsin shut-off causes photoreceptor cell death in arrestin knockout mice.. The retinas of cyclic-light-reared, pigmented arrestin knockout mice and wild-type littermate control mice were examined histologically for photoreceptor cell loss from 100 days to 1 year of age. In separate experiments, to determine whether constant light would accelerate the degeneration in arrestin knockout mice, these animals and wild-type control mice were exposed for 1, 2, or 3 weeks to fluorescent light at an intensity of 115 to 150 fc. The degree of photoreceptor cell loss was quantified histologically by obtaining a mean outer nuclear layer thickness for each animal.. In arrestin knockout mice maintained in cyclic light, photoreceptor loss was evident at 100 days of age, and it became progressively more severe, with less than 50% of photoreceptors surviving at 1 year of age. The photoreceptor degeneration appeared to be caused by light, because when these mice were reared in the dark, the retinal structure was indistinguishable from normal. When exposed to constant light, the retinas of wild-type pigmented mice showed no light-induced damage, regardless of exposure duration. By contrast, the retinas of arrestin knockout mice showed rapid degeneration in constant light, with a loss of 30% of photoreceptors after 1 week of exposure and greater than 60% after 3 weeks of exposure.. The results indicate that constitutive signal flow due to arrestin knockout leads to photoreceptor degeneration. Excessive light accelerates the cell death process in pigmented arrestin knockout mice. Human patients with naturally occurring mutations that lead to nonfunctional arrestin and rhodopsin kinase have Oguchi disease, a form of stationary night blindness. The present findings suggest that such patients may be at greater risk of the damaging effects of light than those with other forms of retinal degeneration, and they provide an impetus to restrict excessive light exposure as a protective measure in patients with constitutive signal flow in phototransduction.

Topics: Animals; Arrestin; Dark Adaptation; Disease Susceptibility; Light; Mice; Mice, Inbred C57BL; Mice, Knockout; Night Blindness; Photoreceptor Cells, Vertebrate; Radiation Injuries, Experimental; Retinal Degeneration; Rhodopsin

Rhodopsin kinase (RK), a rod photoreceptor cytosolic enzyme, plays a key role in the normal deactivation and recovery of the photoreceptor after exposure to light. To date, three different mutations in the RK locus have been associated with Oguchi disease, an autosomal recessive form of stationary night blindness in man characterized in part by delayed photoreceptor recovery [Yamamoto, S. , Sippel, K. C., Berson, E. L. & Dryja, T. P. (1997) Nat. Genet. 15, 175-178]. Two of the mutations involve exon 5, and the remaining mutation occurs in exon 7. Known exon 5 mutations include the deletion of the entire exon sequence [HRK(X5 del)] and a missense change leading to a Val380Asp substitution in the encoded product (HRKV380D). The mutation in exon 7 is a 4-bp deletion in codon 536 leading to premature termination of the encoded polypeptide [HRKS536(4-bp del)]. To provide biochemical evidence for pathogenicity of these mutations, wild-type human rhodopsin kinase (HRK) and mutant forms HRKV380D and HRKS536(4-bp del) were expressed in COS7 cells and their activities were compared. Wild-type HRK catalyzed light-dependent phosphorylation of rhodopsin efficiently. In contrast, both mutant proteins were markedly deficient in catalytic activity with HRKV380D showing virtually no detectible activity and HRKS536(4-bp del) only minimal light-dependent activity. These results provide biochemical evidence to support the pathogenicity of the RK mutations in man.

Topics: Amino Acid Sequence; Animals; COS Cells; Eye Proteins; G-Protein-Coupled Receptor Kinase 1; Humans; Light; Molecular Sequence Data; Mutation; Night Blindness; Phosphorylation; Protein Kinases; Recombinant Proteins; Rhodopsin; Sequence Homology, Amino Acid

A mutation in the gene for the rod photoreceptor molecule rhodopsin causes congenital night blindness. The mutation results in a replacement of Gly90 by an aspartic acid residue. Two molecular mechanisms have been proposed to explain the physiology of affected rod cells. One involves constitutive activity of the G90D mutant opsin [Rao, V. R., Cohen, G. B., & Oprian, D. D. (1994) Nature 367, 639-642]. A second involves increased photoreceptor noise caused by thermal isomerization of the G90D pigment chromophore [Sieving, P. A., Richards, J. E., Naarendorp F., Bingham, E. L., Scott, K., & Alpern, M. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 880-884]. Based on existing models of rhodopsin and in vitro biochemical studies of site-directed mutants, it appears likely that Gly90 is in the immediate proximity of the Schiff base chromophore linkage. We have studied in detail the mutant pigments G90D and G90D/E113A using biochemical and Fourier-transform infrared (FTIR) spectroscopic methods. The photoproduct of mutant pigment G90D, which absorbs maximally at 468 nm and contains a protonated Schiff base linkage, can activate transducin. However, the active photoproduct decays rapidly to opsin and free all-trans-retinal. FTIR studies of mutant G90D show that the dark state of the pigment has several structural features of metarhodopsin II, the active form of rhodopsin. These include a protonated carboxylic acid group at position Glu113 and increased hydrogen-bond strength of Asp83. Additional results, which relate to the structure of the active G90D photoproduct, are also reported. Taken together, these results may be relevant to understanding the molecular mechanism of congenital night blindness caused by the G90D mutation in human rhodopsin.

Topics: Aspartic Acid; Glycine; Humans; Hydroxylamine; Hydroxylamines; Kinetics; Mutagenesis, Site-Directed; Night Blindness; Point Mutation; Recombinant Proteins; Retinal Rod Photoreceptor Cells; Rhodopsin; Rod Opsins; Schiff Bases; Spectroscopy, Fourier Transform Infrared; Transducin

The replacement of Gly90 by Asp in human rhodopsin causes congenital night blindness. It has been suggested that the molecular origin for the trait is an altered electrostatic environment of the protonated retinal Schiff base chromophore. We have investigated the corresponding recombinant bovine rhodopsin mutant G90D, as well as the related mutants E113A and G90D/E113A, using spectroscopy at low temperature. This allows the assessment of chromophore-protein interactions under conditions where conformational changes are mainly restricted to the retinal-binding site. Each of the mutant pigments formed bathorhodopsin- and isorhodopsin-like intermediates, but the concomitant visible absorption changes reflected differences in the electrostatic environment of the protonated Schiff base in each pigment. Fourier transform infrared-difference spectroscopy revealed effects on the chromophore fingerprint and hydrogen-out-of-plane vibrational modes, which were indicative of the removal of an electrostatic perturbation near C12 of the retinal chromophore in all three mutants. A comparison of the UV-visible and infrared-difference spectra of the mutant pigments strongly suggests that Glu113 is stably protonated in G90D. The corresponding carbonyl-stretching mode is assigned to a band at 1727 cm-1. In contrast to the case in native bathorhodopsin, the all-trans-retinal chromophores in the primary photoproducts of the mutant pigments are essentially relaxed. The peptide carbonyl vibrational changes in mutants G90D and G90D/ E113A suggest that this is due to a more flexible retinal-binding site. Therefore, the steric strain exerted on the chromophore in native bathorhodopsin may be caused by electrostatic forces that specifically involve glutamate 113.

Topics: Amides; Animals; Cattle; Electrochemistry; Mutation; Night Blindness; Photochemistry; Recombinant Proteins; Rhodopsin; Schiff Bases; Spectrophotometry, Ultraviolet; Spectroscopy, Fourier Transform Infrared; Temperature

A human rhodopsin mutation, Gly-90-->Asp (Gly90Asp), cosegregated with an unusual trait of congenital nightblindness in 22 at-risk members of a large autosomal dominant kindred. Although rhodopsin mutations typically are associated with retinal degeneration, Gly90Asp-affected subjects up to age 33 did not show clinical retinal changes. Absolute threshold for visual perception was elevated nearly 3 logarithmic units in 7 individuals tested (ages 11-64), indicating greatly compromised rod threshold signaling. However, in vivo rhodopsin density was normal. Although the 38-year-old proband could not perceive dim lights, his rod increment threshold function was normal on brighter backgrounds. The impaired rod vision for dim but not bright backgrounds is consistent with a mechanism of increased basal "dark-light" from thermal isomerization equivalent to an increase of > 10(4) over that of wild-type rhodopsin. The Gly90Asp mutation on the second transmembrane helix places an extra negative charge in the opsin pocket; this could contribute to partial deprotonation of the retinal Schiff base and thereby increase photoreceptor noise. In vitro evidence had suggested that transducin is activated by the Gly90Asp mutation in the absence of both the retinal chromophore and light, termed "constitutive activity." The apparent preservation of functioning rods despite extensive and lifelong night-blindness in this kindred is inconsistent with one current hypothesis that chronic rod activation from constitutively active mutant rhodopsin necessarily contributes significantly to photoreceptor demise in human retinal dystrophies.

Topics: Adolescent; Adult; Base Sequence; Child; Densitometry; DNA Mutational Analysis; Electroretinography; Female; Humans; Male; Middle Aged; Molecular Sequence Data; Night Blindness; Pedigree; Point Mutation; Retinal Rod Photoreceptor Cells; Rhodopsin; Visual Perception

A lysine to glutamic acid substitution at codon 296 in the rhodopsin gene has been reported in a family with autosomal dominant retinitis pigmentosa. This mutation is of particular functional interest as this lysine molecule is the binding site of 11-cis-retinal. The clinical features of a family with this mutation have not been reported previously. We examined 14 patients with autosomal dominant retinitis pigmentosa and a lysine-296-glutamic acid rhodopsin mutation. Four had detailed psychophysical and electrophysiological testing. Most affected subjects had severe disease with poor night vision from early life, and marked reduction of visual acuity and visual field by their early forties. Psychophysical testing showed no demonstrable rod function and severely reduced cone function in all patients tested.

Topics: Adolescent; Adult; Aged; Binding Sites; Dark Adaptation; Electroretinography; Female; Fundus Oculi; Genes, Dominant; Humans; Lysine; Male; Middle Aged; Mutation; Night Blindness; Pedigree; Retinaldehyde; Retinitis Pigmentosa; Rhodopsin; Vision Disorders; Visual Fields

Mutations in the gene for the visual pigment rhodopsin cause retinitis pigmentosa (RP) and congenital night blindness. Inheritance of the diseases is generally autosomal dominant and about 40 different rhodopsin mutations have been documented. Although the cell death and retinal degeneration associated with RP have been suggested to result from improper folding and accumulation of the mutant proteins in rod photoreceptor cells, this may not account for the disease in all cases. For example, RP mutations at Lys 296, site of Schiff base linkage to the retinal chromophore, result in constitutive activation of the protein in vitro; that is, the mutants can catalytically activate the G protein transducin in the absence of chromophore and in the absence of light. Similarly, mutation of Ala 292-->Glu activates opsin in vitro and causes night blindness. We show here that the mutation Gly 90-->Asp (G90D) in the second transmembrane segment of rhodopsin, which causes congenital night blindness, also constitutively activates opsin. Furthermore, we show that Asp 90 can substitute for the Schiff base counterion, Glu 113, which is located in the third transmembrane segment of the protein. This demonstrates the proximity of Asp 90 and Lys 296 in the three-dimensional structure of rhodopsin and suggests that the constitutively activating mutations operate by a common molecular mechanism, disrupting a salt bridge between Lys 296 and the Schiff base counterion, Glu 113.

Topics: Cell Line; Humans; Mutation; Night Blindness; Protein Conformation; Rhodopsin; Schiff Bases

Twenty five symptomatic individuals and six asymptomatic obligate gene carriers from four families with autosomal dominant retinitis pigmentosa (adRP) showing apparent incomplete penetrance have been studied. Symptomatic individuals from three families showed early onset of night blindness, non-recordable rod electroretinograms, and marked elevation of both rod and cone thresholds in all subjects tested. In the fourth family, there was more variation in the age of onset of night blindness and some symptomatic individuals showed well preserved rod and cone function in some retinal areas. All asymptomatic individuals tested had evidence of mild abnormalities of rod and cone function, indicating that these families show marked variation in expressivity rather than true non-penetrance of the adRP gene. No mutations of the rhodopsin or RDS genes were found in these families and the precise genetic mutation(s) remain to be identified.

Topics: Adolescent; Adult; Chromosomes, Human, Pair 7; Electrophysiology; Electroretinography; Female; Genetic Linkage; Heterozygote; Humans; Male; Middle Aged; Night Blindness; Pedigree; Photoreceptor Cells; Psychophysics; Retinal Degeneration; Retinitis Pigmentosa; Rhodopsin; Sensory Thresholds; Visual Fields

A family is described in which an 8 base pair deletion (nucleotides 5252-5259, codons 341-343) of the rhodopsin gene cosegregates with autosomal dominant retinitis pigmentosa (adRP). The deletion results in a shift in the reading frame, causing a rhodopsin molecule extended by one residue and substantially altered at the carboxyl terminus. Phenotypic expression is relatively mild. In affected members, night blindness did not occur before the age of 16, and late onset of visual field loss was consistently reported. Even older individuals (59 and 76 years) had preserved central islands in the visual field; a younger female patient had normal visual fields until the age of 34. ERG and psychophysical tests showed well preserved cone function at stages of virtually abolished rod function. Phenotypic differences and similarities between this form of adRP and others associated with mutations at the carboxyl terminus of the rhodopsin molecule are discussed. The cause of RP by mutations in this region remains to be clarified.

Topics: Adult; Aged; Amino Acid Sequence; Base Sequence; Carboxylic Acids; Child, Preschool; Electroretinography; Female; Fluorescein Angiography; Frameshift Mutation; Fundus Oculi; Gene Deletion; Humans; Male; Middle Aged; Molecular Sequence Data; Night Blindness; Pedigree; Phenotype; Photoreceptor Cells; Retinitis Pigmentosa; Rhodopsin; Vision Disorders; Visual Fields

Ten rhodopsin mutations have been found in a screen of 282 subjects with retinitis pigmentosa (RP), 76 subjects with Leber congenital amaurosis, and 3 subjects with congenital stationary night blindness. Eight of these mutations (gly51-to-ala, val104-to-ile, gly106-to-arg, arg135-to-gly, cys140-to-ser, gly188-to-glu, val209-to-met, and his211-to-arg) produce amino acid substitutions, one (gln64-to-ter) introduces a stop codon, and one changes a guanosine in the intron 4 consensus splice donor sequence to thymidine. Cosegregation of RP with gln64-to-ter, gly106-to-arg, arg135-to-gly, cys140-to-ser, gly188-to-glu, his211-to-arg, and the splice site guanosine-to-thymidine indicates that these mutations are likely to cause retinal disease. Val104-to-ile does not cosegregate and is therefore unlikely to be related to retinal disease. The relevance of gly51-to-ala and val209-to-met remains to be determined. The finding of gln64-to-ter in a family with autosomal dominant RP is in contrast to a recent report of a recessive disease phenotype associated with the rhodopsin mutation glu249-to-ter. In the present screen, all of the mutations that cosegregate with retinal disease were found among patients with RP. The mutations described here bring to 35 the total number of amino acid substitutions identified thus far in rhodopsin that are associated with RP. The distribution of the substitutions along the polypeptide chain is significantly nonrandom: 63% of the substitutions involve those 19% of amino acids that are identical among vertebrate visual pigments sequenced to date.

Topics: Alleles; Blindness; DNA Mutational Analysis; Female; Gene Frequency; Humans; Male; Mutation; Night Blindness; Pedigree; Polymerase Chain Reaction; Protein Conformation; Retinitis Pigmentosa; Rhodopsin

Scotopic visual thresholds and time courses for dark adaptation were determined in eight patients with Sorsby's fundus dystrophy. Rhodopsin regeneration also was recorded in two. All patients had poor night vision and a visible yellow deposit at the level of Bruch's membrane that was confluent in the posterior pole. In retinal regions with the yellow deposit, scotopic thresholds were elevated, the rod-cone break was delayed or indistinct, the time courses for the rod portion of the dark adaptation curve was prolonged, and rhodopsin regeneration was slow in the one patient in whom measurements were made. In regions of ophthalmoscopically normal retina, dark adaptation was affected minimally, and in one patient, rhodopsin was regenerated at a normal rate. It was hypothesized that the abnormal dark adaptation and rhodopsin kinetics might be caused by reduced metabolic exchange across a thickened Bruch's membrane.

Topics: Adult; Bruch Membrane; Dark Adaptation; Fundus Oculi; Humans; Kinetics; Middle Aged; Night Blindness; Retinal Degeneration; Rhodopsin; Sensory Thresholds; Vision Disorders

Four members in a Japanese family had autosomal dominant retinitis pigmentosa caused by a single point mutation in codon 347 of the rhodopsin gene. The youngest, an 11-year-old girl, had an abnormal electroretinographic response, although her fundus appeared normal. The other affected family members noticed night blindness in the second decade. Their fundi showed diffuse pigmentation with concentric visual field loss, and there was no recordable electroretinographic response. Cataract developed in the fourth decade in the older patients. Good visual acuity was retained however, even in the fifth decade, after cataract extraction. These clinical features were similar to those of American patients (European family origin) with the same mutation of the rhodopsin gene reported previously.

Topics: Adult; Aged; Cataract; Child; Codon; DNA; Electroretinography; Female; Fundus Oculi; Humans; Japan; Male; Mutagenesis, Site-Directed; Night Blindness; Pedigree; Retinitis Pigmentosa; Rhodopsin; Visual Fields

DNA samples from 161 unrelated patients with autosomal dominant retinitis pigmentosa were screened for point mutations in the rhodopsin gene by using the polymerase chain reaction and denaturing gradient gel electrophoresis. Thirty-nine patients were found to carry 1 of 13 different point mutations at 12 amino acid positions. The presence or absence of the mutations correlated with the presence or absence of retinitis pigmentosa in 174 out of 179 individuals tested in 17 families. The mutations were absent from 118 control subjects with normal vision.

Topics: Base Sequence; DNA; Female; Genes; Genes, Dominant; Humans; Male; Molecular Sequence Data; Mutation; Night Blindness; Nucleic Acid Hybridization; Oligonucleotide Probes; Pedigree; Polymerase Chain Reaction; Retinitis Pigmentosa; Rhodopsin; Visual Fields

We studied the ocular findings in eight unrelated patients with a form of autosomal dominant retinitis pigmentosa and the same cytosine-to-thymine transition in the second nucleotide of codon 347 of the rhodopsin gene. This mutation, detected in leukocyte DNA, corresponds to a substitution of leucine for proline in amino acid 347 of the rhodopsin protein, and, therefore, we designated this form of retinitis pigmentosa as rhodopsin, proline-347-leucine. On average, these patients had significantly smaller visual field areas and smaller electroretinogram amplitudes than 140 unrelated patients of comparable age with dominant retinitis pigmentosa without this mutation. The findings in eight relatives with this mutation from three of these families are presented to provide examples of the variability that exists in the clinical severity of this disease.

Topics: Adolescent; Adult; Amino Acid Sequence; Chromosome Aberrations; Chromosome Disorders; Dark Adaptation; Electroretinography; Female; Fundus Oculi; Humans; Leucine; Male; Middle Aged; Molecular Sequence Data; Mutation; Night Blindness; Pedigree; Proline; Retinitis Pigmentosa; Rhodopsin; Visual Fields

We report findings obtained from an individual with an unusual form of congenital stationary night blindness (CSNB). Although the rhodopsin density difference of this subject was normal, there was no evidence of rod-mediated visual function. Dark-adapted thresholds were cone-mediated, and dark-adapted electroretinograms (ERGs) represented activity of the cone system exclusively. ERG a- and b-waves obtained under light-adapted conditions were normal. The absence of a rod a-wave but the presence of normal rhodopsin density, in combination with normal cone function, indicates that this form of CSNB likely involves a defect of phototransduction that is limited to the rods. In addition, light-adapted b-wave responses to high luminance flashes were larger than dark-adapted responses, whereas a-wave amplitudes were reduced by light adaptation. These ERG results address proposed mechanisms by which light adaptation might enhance cone system responses.

Topics: Adolescent; Dark Adaptation; Electroretinography; Female; Fundus Oculi; Humans; Image Processing, Computer-Assisted; Light; Male; Night Blindness; Photoreceptor Cells; Retina; Rhodopsin; Sensory Thresholds; Visual Acuity

Photoreceptor-mediated mechanisms were studied in patients with a recently identified retinopathy typified by night blindness, cystoid maculopathy, and similar scotopic and photopic electroretinograms (ERGs). Dark-adapted spectral sensitivity functions were only partly explained as composites of rod and cone curves shifted to lower sensitivities; there was unusually high sensitivity from 400-460 nm. A rod mechanism, reduced in sensitivity by at least 3 log units, was detectable with dark adaptometry. No measurable rhodopsin was found with fundus reflectometry. Light-adapted spectral sensitivities were subnormal for wavelengths greater than 500 nm but supernormal from 420-460 nm. On a yellow adapting field, the supernormal spectrum approximated that of the short-wavelength-sensitive (SWS) cone system. With spectral ERGs, two mechanisms were demonstrated. Dark- and light-adapted ERGs to green, orange-yellow, and red stimuli had similar waveforms and coincident intensity-response functions on a photopic intensity axis. ERGs to blue and blue-green stimuli were similar, and intensity-response functions coincided on a SWS cone intensity axis. Patients varied in the degree to which rod and midspectral cone function were decreased and SWS cone function was increased.

Topics: Adolescent; Adult; Child; Dark Adaptation; Electroretinography; Female; Fundus Oculi; Humans; Macular Degeneration; Male; Middle Aged; Night Blindness; Photoreceptor Cells; Psychophysics; Retinal Degeneration; Rhodopsin; Sensory Thresholds; Visual Acuity; Visual Field Tests

A healthy, 14-year-old girl presented with nyctalopia, good vision, and multiple, irregular, yellowish lesions of the fundus. Dark adaptometry showed prolonged cone and rod branches, elevated thresholds, and the cone-rod transition occurring after 50 minutes in darkness. Her scotopic electroretinogram (ERG) b-wave attained normal amplitudes after 45 minutes of dark adaptation. The half-time for regeneration of rhodopsin after an extensive bleach was 16 minutes, four times longer than normal, and the maximum density difference measured by fundus reflectometry was at the lower limit of the normal range. Although photopigment kinetics were significantly faster than observed in other reported cases of fundus albipunctatus, it appears likely that there is a wide spectrum of functional and funduscopic abnormalities in this disorder. However, fundus appearance, adaptometric findings, and rhodopsin determinations serve to distinguish fundus albipunctatus from other flecked retina diseases.

Topics: Adolescent; Dark Adaptation; Electroretinography; Female; Fluorescein Angiography; Fundus Oculi; Humans; Night Blindness; Retinal Diseases; Rhodopsin

Various noninvasive test procedures were used to evaluate retinal function in a patient who had become night blind following vincristine chemotherapy. The results obtained were strikingly similar to those reported previously in subjects with recessively inherited stationary night blindness; the dark-adaptation curve was monophasic (ie, no evidence of a scotopic branch), rhodopsin kinetics were entirely normal, and spectral threshold data revealed the presence of residual rod-mediated vision. Also like the heritable condition, the b-wave of the ERG was depressed grossly despite normal a-wave potentials. These findings, and the fact that vincristine is known to disrupt the structural integrity of neuronal microtubules, suggest that the drug-induced defect involves the process of synaptic transmission between the photoreceptors and their second-order neurons.

Topics: Adaptation, Ocular; Adult; Dark Adaptation; Electrooculography; Electroretinography; Humans; Light; Male; Night Blindness; Photoreceptor Cells; Retina; Rhodopsin; Synapses; Synaptic Transmission; Vincristine

Night blindness is a frequent concomitant of retinal disorders, many of which are of genetic origin. Through the use of quantitative noninvasive test procedures it has been possible to study patients with these hereditary conditions and to show that the visual abnormalities often result from defects in the functional properties of the rod photoreceptors. More important, the uniqueness of the functional disturbance in the various types of night-blinding disorders suggests that each involves a specific aspect of the rod's internal machinery, i.e., the molecular processes devoted to transduction, intercellular communication, and the renewal of cellular components. Knowledge gained from the study of these clinical entities and from the investigation of experimental animals regarding the cellular events involved in these vital processes have enabled us to formulate tentative hypothesis as to the molecular bases of the hereditary defects.

Topics: Genetic Diseases, Inborn; Horseradish Peroxidase; Humans; Neuromuscular Junction; Neurotransmitter Agents; Night Blindness; Photoreceptor Cells; Retinal Diseases; Retinitis Pigmentosa; Rhodopsin; Synapses; Synaptic Transmission

Three unrelated boys, ages 2, 6, and 10 years, who have congenital stationary night blindness with myopia and a Schubert-Bornschein-type electroretinogram finding, were found to show a "paradoxical" pupillary constriction in darkness. When examining room lights are turned out, the patient's pupils briskly constrict and slowly dilate. Older night blind male relatives of these boys did not show this abnormal constriction to darkness.

Topics: Adolescent; Adult; Child; Child, Preschool; Electroretinography; Female; Humans; Infant; Infant, Newborn; Male; Middle Aged; Myopia; Night Blindness; Nystagmus, Pathologic; Reflex, Pupillary; Rhodopsin; Strabismus

An account is given of investigations into the mechanisms of dark-adaptation in the retina of man and of the skate and other fish. Working hypotheses as to the possible sites of abnormal function in the various disorders of which night blindness is a feature are presented.

Topics: Animals; Dark Adaptation; Electrophysiology; Electroretinography; Fishes; Humans; Night Blindness; Photoreceptor Cells; Retina; Retinitis; Rhodopsin; Vision Disorders

Topics: Acetates; Administration, Oral; Animals; Body Weight; Dose-Response Relationship, Drug; Electroretinography; Injections, Intraperitoneal; Isomerism; Male; Night Blindness; Organ Specificity; Rats; Retina; Rhodopsin; Testis; Vitamin A; Vitamin A Deficiency