SMALL INCREASE IN TRIPLET REPEAT LENGTH OF CEREBELLUM FROM PATIENTS WITH MYOTONIC-DYSTROPHY

Myotonic dystrophy (DM) is genetically characterized by abnormal expan sion of an unstable CTG trinucleotide repeat, located in the 3'-untran slated region of mRNA encoding the family of serine-threonine protein kinases. DNA extracted from various organs of patients with DM was ana lyzed by the Southern blotting method. We identified differently expan ded bands in DNAs from various tissues from patients with DM. In study ing the length of the CTG repeat in different regions of the brain, we found a noticeably small increase in repeat length in the cerebellum compared with other tissues. While this phenomenon has been reported i n other tripler repeat diseases such as Huntington disease, spinocereb ellar ataxia type 1, and dentatorubral-pallidoluysian atrophy, we are the first to describe it in DM. Although the mechanism of expansion of the triplet repeat remains to be defined, the tissue-dependent somati c mosaicism suggests that its occurrence may depend on the differentia ted state of each tissue.