Elongation of (CTG)n repeats in myotonic dystrophy protein kinase gene in tumors associated with myotonic dystrophy patients.

Length of (CTG)n triplet repeats in myotonic dystrophy protein kinase gene (DMPK) was estimated in tumors, normal tissues of the same organs, muscles, and leukocytes from three myotonic dystrophy (DM) patients and a non-DM patient. Using cDNA 25 as a probe, a Southern blot analysis of EcoRI- and BglI-digested DNA from these tissues demonstrated the longest expansion of the repeats in the tumors of DM patients. In all tissues from a non-DM patient, the repeat length was confirmed to be stable by PCR analysis. Our data suggest that expanded (CTG)n repeat in tumor tissues may have increased the instability. This study emphasizes the importance of a long-term prospective study on the incidence of tumors in DM to clarify the pathological interrelation between the two entities.