Minimal somatic instability of CTG repeat in congenital myotonic dystrophy.

The molecular basis of myotonic dystrophy was identified as an unstable trinucleotide (CTG) repeat in the 3' untranslated region of an mRNA encoding a member of the protein kinase family. Unstable DNA was analyzed from various tissue samples of a patient with severe congenital myotonic dystrophy. In BamHI- or BglI-digested DNA, a normal band plus differently expanded ones were identified in various tissue samples. These observations demonstrated somatic instability of the repeat in a congenital myotonic dystrophy patient.