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.
- Molecular genetics
- neuromuscular disease
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Funding This work has been supported by grants from the Fund for Scientific Research Flanders (Fonds voor Wetenschappelijk Onderzoek Vlaanderen (FWO Vlaanderen), Egmontstraat 5, 1000 Brussels, Belgium. CS is a postdoctoral fellow at the FWO Vlaanderen.
Competing interests None.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the Commissie Medische Ethiek Universitair Ziekenhuis Brussel.
Provenance and peer review Not commissioned; externally peer reviewed.