Evidence for a relatively high proportion of DM2 mutations in a large group of Polish patients.

Introduction: Myotonic dystrophies (DMs) type 1 (DM1) and type 2 (DM2) are autosomal dominant, multisystem disorders, considered the most common dystrophies in adults. DM1 and DM2 are caused by dynamic mutations in the DMPK and CNBP genes, respectively.

Methods: Molecular analyses were performed by PCR and the modified RP-PCR in patients, in their at-risk relatives and prenatal cases.

Results: The analysis of Polish controls revealed the range of 5-31 CTG repeats for DM1 and 110-228 bp alleles for DM2. Among 318 confirmed probands - 196 (62%) were DM1 and 122 (38%) - DM2. Within DM1families, 10 subjects carried a low expanded CTG tract (< 100 repeats), which resulted in a full mutation in subsequent generations. Two related individuals had unstable alleles-188 bp and 196 bp without common interruptions.

Conclusion: The relative frequencies of DM1/DM2 among Polish patients were 68% and 32%, respectively, with a relatively high proportion of DM2 mutations (1.6:1).