cytidylyl-3--5--guanosine and Myotonic-Dystrophy

We have studied the methylation status of the sequence 152 nucleotides upstream of the CTG repeat of the DM1 locus in patients' peripheral blood. We used the methylation-sensitive endonucleases SacII, HpaII and HhaI, followed by PCR. This allowed to correlate the methylation status of each CTG allele with its size. Contrary to previous findings, only the SacII site is often but not always differentially methylated among expanded CTG alleles. Importantly, this methylation was not restricted to congenital DM1, nor to large expansions, as it was also present in DM1 patients with a classical phenotype and various expansion sizes. On the other hand, we did not find any methylated alleles on the HhaI and HpaII sites, as was reported by Steinbach et al, which is in line with the results of Shaw and collaborators. The size range of the repeat expansions with methylation was from as small as 300 to as large as 2800 repeats.

Topics: Base Sequence; Dinucleoside Phosphates; Endonucleases; Humans; Methylation; Molecular Sequence Data; Myotonic Dystrophy; Myotonin-Protein Kinase; Phenotype; Polymerase Chain Reaction; Protein Serine-Threonine Kinases; Trinucleotide Repeat Expansion; Trinucleotide Repeats

Myotonic dystrophy (DM) is associated with a (CTG)n trinucleotide repeat expansion in the 3'-untranslated region of a protein kinase-encoding gene, DMPK, which maps to chromosome 19q13.3. Characterisation of the expression of this gene in patient tissues has thus far generated conflicting data on alterations in the steady state levels of DMPK mRNA, and on the final DMPK protein levels in the presence of the expansion. The DM region of chromosome 19 is gene rich, and it is possible that the repeat expansion may lead to dysfunction of a number of transcription units in the vicinity, perhaps as a consequence of chromatin disruption. We have searched for genes associated with a CpG island at the 3' end of DMPK. Sequencing of this region shows that the island extends over 3.5 kb and is interrupted by the (CTG)n repeat. Comparison of genomic sequences downstream (centromeric) of the repeat in human and mouse identified regions of significant homology. These correspond to exons of a gene predicted to encode a homeodomain protein. RT-PCR analysis shows that this gene, which we have called DM locus-associated homeodomain protein (DMAHP), is expressed in a number of human tissues, including skeletal muscle, heart and brain.

Topics: Amino Acid Sequence; Animals; Base Sequence; Brain; Centromere; Chromosome Mapping; Chromosomes, Human, Pair 19; Cloning, Molecular; Dinucleoside Phosphates; Exons; Gene Expression; Gene Library; Genes, Homeobox; Homeodomain Proteins; Humans; Mice; Molecular Sequence Data; Muscle, Skeletal; Myocardium; Myotonic Dystrophy; Myotonin-Protein Kinase; Organ Specificity; Polymerase Chain Reaction; Protein Serine-Threonine Kinases; Repetitive Sequences, Nucleic Acid; Sequence Homology, Amino Acid; Sequence Homology, Nucleic Acid; Transcription, Genetic