cobamamide and Metabolism--Inborn-Errors

Topics: Cobamides; Diagnosis, Differential; Humans; Metabolism, Inborn Errors; Methylmalonic Acid; Prognosis; Vitamin B 12

Topics: 5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; Animals; Bacterial Proteins; Biological Evolution; Biological Transport; Cells, Cultured; Child; Cobamides; Female; Fibroblasts; Genes; Genetic Complementation Test; Homocystinuria; Humans; Incidence; Infant, Newborn; Intestinal Absorption; Intrinsic Factor; Male; Metabolism, Inborn Errors; Methylmalonic Acid; Methylmalonyl-CoA Mutase; Mice; Transcobalamins; Vitamin B 12; Vitamin B Deficiency

Topics: Cobamides; Humans; Lysosomes; Metabolism, Inborn Errors; Methylmalonic Acid; NADH, NADPH Oxidoreductases; Vitamin B 12

Combined methylmalonic aciduria and homocystinuria cobalamin C type (cobalamin C disease) is an inborn metabolic disorder consisting of an impaired intracellular synthesis of the 2 active forms of vitamin B12 (cobalamin), namely, adenosylcobalamin and methylcobalamin, that results in increased levels of methylmalonic acid and homocysteine in the blood and urine. Most patients present in the first year of life with systemic, hematological, and neurological abnormalities. Late-onset forms are rare and had not been comprehensively characterized. They could be easily misdiagnosed.. To describe clinical and biochemical features of the disease in 2 siblings affected with presumed late-onset cobalamin C disease.. Case report and review of the literature.. Neurological intensive care unit of a university hospital.. We describe 2 patients with neurological deterioration due to presumed cobalamin C disease. A 16-year-old girl was initially seen with psychosis and severe progressive neuropathy requiring mechanical ventilatory support and her 24-year-old sister had a 2-year disease course of subacute combined degeneration of the spinal cord. A metabolic workup displayed increased methylmalonic acid levels, severe hyperhomocysteinemia, and low plasma methionine levels. The diagnosis was then confirmed by demonstration of impaired synthesis of adenosylcobalamin and methylcobalamin in cultured skin fibroblasts and Epstein-Barr virus-infected lymphocytes. Under specific treatment the younger sister's condition dramatically improved.. Although complementation studies have not been conducted, it is most likely these patients had cobalamin C disease. This study emphasizes the possibility of late-onset disease with purely neurological manifestations. Left untreated, this treatable condition can lead to death or irreversible damage to the nervous system. Screening for intracellular vitamin B12 dysmetabolism should, therefore, be considered in the investigation of adults with unexplained neurological disease, particularly when they are initially seen with a clinical picture suggestive of vitamin B12 deficiency.

Topics: Adolescent; Adult; Brain; Cobamides; Female; Fibroblasts; Homocysteine; Humans; Mental Disorders; Metabolism, Inborn Errors; Methylmalonic Acid; Nervous System Diseases; Sural Nerve; Vitamin B 12

Derivatives of cobalamin (vitamin B(12)) are required for activity of two enzymes in humans. Adenosylcobalamin is required for activity of mitochondrial methylmalonylCoA mutase and methylcobalamin is required for activity of cytoplasmic methionine synthase. Deficiency in cobalamin, or inability to absorb cobalamin normally, can result in accumulation of methylmalonic acid and homocysteine in blood and urine. Methylmalonic acidemia can result in metabolic acidosis which in severe cases may be fatal. Hyperhomocysteinemia along with hypomethioninemia can result in hematologic (megaloblastic anemia, neutropenia, thrombocytopenia) and neurologic (subacute combined degeneration of the cord, dementia, psychosis) defects. Inborn errors affecting cobalamin absorption (inherited intrinsic factor deficiency, Imerslund–Gra¨ sbeck syndrome) and transport (transcobalamin deficiency) have been described. A series of inborn errors of intracellular cobalamin metabolism, designated cblA-cblG, have been differentiated by complementation analysis. These can give rise to isolated methylmalonic acidemia (cblA, cblB, cblD variant 2), isolated hyperhomocysteinemia (cblD variant 1, cblE, cblG) or combined methylmalonic acidemia and hyperhomocysteinemia (cblC, classic cblD, cblF). All these disorders are inherited as autosomal recessive traits. The genes underlying each of these disorders have been identified. Two other disorders, haptocorrin deficiency and transcobalamin receptor deficiency, have been described, but it is not clear that they have any consistent clinical phenotype.

Topics: Amino Acid Metabolism, Inborn Errors; Anemia, Megaloblastic; Cobamides; Homocysteine; Humans; Hyperhomocysteinemia; Infant, Newborn; Malabsorption Syndromes; Metabolism, Inborn Errors; Methylmalonic Acid; Methylmalonyl-CoA Mutase; Neonatal Screening; Proteinuria; Vitamin B 12; Vitamin B 12 Deficiency

Vitamin B(12) (cobalamin, Cbl) is essential to the function of two human enzymes, methionine synthase (MS) and methylmalonyl-CoA mutase (MUT). The conversion of dietary Cbl to its cofactor forms, methyl-Cbl (MeCbl) for MS and adenosyl-Cbl (AdoCbl) for MUT, located in the cytosol and mitochondria, respectively, requires a complex pathway of intracellular processing and trafficking. One of the processing proteins, MMAA (methylmalonic aciduria type A), is implicated in the mitochondrial assembly of AdoCbl into MUT and is defective in children from the cblA complementation group of cobalamin disorders. To characterize the functional interplay between MMAA and MUT, we have crystallized human MMAA in the GDP-bound form and human MUT in the apo, holo, and substrate-bound ternary forms. Structures of both proteins reveal highly conserved domain architecture and catalytic machinery for ligand binding, yet they show substantially different dimeric assembly and interaction, compared with their bacterial counterparts. We show that MMAA exhibits GTPase activity that is modulated by MUT and that the two proteins interact in vitro and in vivo. Formation of a stable MMAA-MUT complex is nucleotide-selective for MMAA (GMPPNP over GDP) and apoenzyme-dependent for MUT. The physiological importance of this interaction is highlighted by a recently identified homoallelic patient mutation of MMAA, G188R, which, we show, retains basal GTPase activity but has abrogated interaction. Together, our data point to a gatekeeping role for MMAA by favoring complex formation with MUT apoenzyme for AdoCbl assembly and releasing the AdoCbl-loaded holoenzyme from the complex, in a GTP-dependent manner.

Topics: Child; Child, Preschool; Cobamides; Crystallography, X-Ray; Cytosol; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Membrane Transport Proteins; Metabolism, Inborn Errors; Methylmalonyl-CoA Mutase; Mitochondria; Mitochondrial Membrane Transport Proteins; Mitochondrial Proteins; Multiprotein Complexes; Mutation, Missense; Protein Structure, Quaternary

The mechanism by which docking fidelity is achieved for the multitude of cofactor-dependent enzymes is poorly understood. In this study, we demonstrate that delivery of coenzyme B(12) or 5'-deoxyadenosylcobalamin by adenosyltransferase to methylmalonyl-CoA mutase is gated by a small G protein, MeaB. While the GTP-binding energy is needed for the editing function; that is, to discriminate between active and inactive cofactor forms, the chemical energy of GTP hydrolysis is required for gating cofactor transfer. The G protein chaperone also exerts its editing function during turnover by using the binding energy of GTP to elicit release of inactive cofactor that is occasionally formed during the catalytic cycle of MCM. The physiological relevance of this mechanism is demonstrated by a patient mutation in methylmalonyl-CoA mutase that does not impair the activity of this enzyme per se but corrupts both the fidelity of the cofactor-loading process and the ejection of inactive cofactor that forms occasionally during catalysis. Consequently, cofactor in the incorrect oxidation state gains access to the mutase active site and is not released if generated during catalysis, leading, respectively, to assembly and accumulation of inactive enzyme and resulting in methylmalonic aciduria.

Topics: Base Sequence; Calorimetry; Cobamides; DNA Primers; Electron Spin Resonance Spectroscopy; GTP-Binding Proteins; Guanosine Triphosphate; Humans; Kinetics; Metabolism, Inborn Errors; Methylmalonic Acid; Methylmalonyl-CoA Mutase; Models, Molecular; Mutation; Thermodynamics

Inborn errors of vitamin B12 (cobalamin, Cbl) metabolism are autosomal recessive disorders and have been classified into nine distinct complementation classes (cblA-cblH and mut). Disorders affecting methylcobalamin metabolism cause megaloblastic anemia, which may be accompanied by leukopenia and thrombocytopenia, and a variety of neurological problems. Disorders affecting adenosylcobalamin cause methylmalonic acidemia and metabolic acidosis. Previous studies have shown that cobalamin binds to two enzymes in humans: methylmalonyl-CoA mutase in mitochondria and methionine synthase in the cytosol. In this study, cobalamin binding patterns were analyzed in crude mitochondrial fractions obtained from both control and patient fibroblasts that had been incubated with [57Co]cyanocobalamin. Crude mitochondrial fractions from control fibroblasts confirmed that the majority of [57Co]Cbl eluted with methylmalonyl-CoA mutase. However, in six of the nine disorders, at least one previously unidentified mitochondrial cobalamin binding protein was observed to bind [57Co]Cbl. The proportion of [57Co]Cbl that binds, is increased compared to controls when a deficiency in either adenosylcobalamin synthesis or utilization prevents binding to methylmalonyl-CoA mutase. Furthermore, unique cobalamin binding profiles emerged demonstrating how known mutations in these patients affect cobalamin binding to as yet unidentified proteins.

Topics: Case-Control Studies; Cell Line; Chromatography, Gel; Cobamides; Enzymes; Fibroblasts; Genetic Complementation Test; Humans; Metabolism, Inborn Errors; Methylmalonyl-CoA Mutase; Mitochondrial Proteins; Transcobalamins; Vitamin B 12

Renal tubular dysfunction and chronic renal failure are well recognised complications of methylmalonic acidaemia (MMA) and can occur even in the context of optimal medical metabolic management. Organ transplantation, such as renal and combined liver and renal transplants, have been utilised in the past for children whose disease cannot be managed by conservative medical practices and those with end stage renal disease. Our patient was diagnosed with B(12)-responsive MMA (subsequently proven to be cblA-type MMA) in the postoperative period following renal transplantation for idiopathic chronic renal failure. She remains well, with excellent graft function and metabolic control 4 years after transplantation. This patient highlights the importance of testing for the inborn errors of metabolism in patients presenting with recurrent acidosis and progressive renal impairment.

Topics: Adolescent; Cobamides; Female; Humans; Kidney Failure, Chronic; Kidney Transplantation; Metabolism, Inborn Errors; Methylmalonic Acid; Vitamin B 12

Mutations in the MMAA gene on human chromosome 4q31.21 result in vitamin B12-responsive methylmalonic aciduria (cblA complementation group) due to deficiency in the synthesis of adenosylcobalamin. Genomic DNA from 37 cblA patients, diagnosed on the basis of cellular adenosylcobalamin synthesis, methylmalonyl-coenzyme A (CoA) mutase function, and complementation analysis, was analyzed for deleterious mutations in the MMAA gene by DNA sequencing of exons and flanking sequences. A total of 18 novel mutations were identified, bringing the total number of mutations identified in 37 cblA patients to 22. A total of 13 mutations result in premature stop codons; three are splice site defects; and six are missense mutations that occur at highly conserved residues. Eight of these mutations were common to two or more individuals. One mutation, c.433C>T (R145X), represents 43% of pathogenic alleles and a common haplotype was identified. Restriction endonuclease or heteroduplex diagnostic tests were designed to confirm mutations. None of the sequence changes identified in cblA patients were found in 100 alleles from unrelated control individuals.

Topics: Child, Preschool; Chromosomes, Human, Pair 4; Cobamides; DNA Mutational Analysis; Exons; Female; Genetic Complementation Test; Haplotypes; Humans; Infant; Infant, Newborn; Male; Membrane Transport Proteins; Metabolism, Inborn Errors; Methylmalonic Acid; Mitochondrial Membrane Transport Proteins; Mitochondrial Proteins; Mutation; Polymorphism, Single Nucleotide; Vitamin B 12

We report the successful treatment of a woman with Cobalamin A disease with hydroxycobalamin injections during pregnancy and delivery and 3 months after delivery. Urine and plasma methylmalonic acid levels served to adjust therapy before and after delivery. The mother had no untoward metabolic complications and gave birth to a normal baby.

Topics: Cobamides; Female; Humans; Hydroxocobalamin; Metabolism, Inborn Errors; Methylmalonic Acid; Pregnancy; Pregnancy Complications; Vitamin B 12

To investigate genetic heterogeneity within the cblA class of inborn error of cobalamin metabolism.. The cblA disorder is characterised by vitamin B12 (cobalamin) responsive methylmalonic aciduria and deficient synthesis of adenosylcobalamin, required for activity of the mitochondrial enzyme methylmalonyl CoA mutase. The cblA gene has not been identified or cloned. We have previously described a patient with the clinical and biochemical phenotype of the cblA disorder whose fibroblasts complemented cells from patients with all known types of inborn error of adenosylcobalamin synthesis, including cblA.. We have performed somatic cell complementation analysis of the cblA variant fibroblast line with a panel of 28 cblA lines. We have also performed detailed complementation analysis on a panel of 10 cblA fibroblast lines, not including the cblA variant line.. The cblA variant line complemented all 28 cell lines of the panel. There was evidence for interallelic complementation among the 10 cblA lines used for detailed complementation analysis; no cell line in this panel complemented all other members.. These results strongly suggest that the cblA variant represents a novel complementation class, which we have designated cblH and which represents a mutation at a distinct gene. They also suggest that the cblA gene encodes a protein that functions as a multimer, allowing for extensive interallelic complementation.

Topics: Alleles; Cell Line; Cobamides; Fibroblasts; Genetic Complementation Test; Humans; Metabolism, Inborn Errors; Methylmalonyl-CoA Mutase; Vitamin B 12

A 16-month-old boy was hospitalized because of a 1-day history of severe ketoacidosis with lethargy, hypotonia, vomiting, and important dyspnoea. Organic acid assay by gas chromatography-mass spectrometry confirmed the diagnosis of methylmalonic acidaemia (MMA). On the sixteenth day, he developed an acute extrapyramidal disorder. The CT scan of the brain disclosed bilaterally symmetric lucency of basal ganglia. He died at 17 months of age. Post-mortem neuropathological examination, showed severe necrosis with spongiosis, cystic cavitation and numerous lipid-laden macrophages of the globi pallidi, and mild spongiosis of subthalamic nuclei, mammillary bodies, portion of internal capsule adjacent to globus pallidus, superior cerebellar peduncles and tegmentum of brainstem. Pallidal infarction, a focal ischaemic lesion, demonstrates that ischaemia/energy depletion may be important in the etiology of the neuropathology of MMA.

Topics: Cobamides; Fatal Outcome; Globus Pallidus; Humans; Infant; Male; Metabolism, Inborn Errors; Methylmalonic Acid; Methylmalonyl-CoA Mutase

Several of the inborn errors of vitamin B12 (cobalamin, Cbl) metabolism (cblC, cblD, cblE, cblF, cblG) are associated with homocystinuria and hypomethioninemia due to a functional deficiency of the cytoplasmic enzyme methionine synthase which requires methylcobalamin (MeCbl) as a cofactor. We compared the growth of cultured fibroblasts from controls, from patients with a selective deficiency of MeCbl (cblE and cblG), with those with a defect in both MeCbl and adenosylcobalamin (AdoCbl) (cblC, cblD and cblF), in methionine and folic acid-free media to their growth in fully supplemented medium. Control cells were able to grow in deficient medium supplied with homocysteine, cobalamin and folate, while mutant cells were not, due to their inability to synthesize methionine from its immediate metabolic precursor, homocysteine. This differential growth is useful in screening for genetic defects of methionine biosynthesis.

Topics: 5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; Cell Division; Cell Line; Cobamides; Fibroblasts; Homocysteine; Humans; Metabolism, Inborn Errors; Methionine; Vitamin B 12; Vitamin B 12 Deficiency