COMPARISON OF CTG REPEAT LENGTH EXPANSION AND CLINICAL PROGRESSION OFMYOTONIC-DYSTROPHY OVER A 5-YEAR PERIOD

Myotonic dystrophy (DM) is associated with an underlying CTG trinucleo tide repeat expansion at a locus on chromosome 19q13.3. We have determ ined the repeat length in 23 DM patients with varying clinical severit y of symptoms and various sizes of repeat amplification. We confirm th at as in previous studies there is no strong correlation between repea t length and clinical symptoms but find that the repeat length in peri pheral blood cells of patients increases over a time span of five year s indicating continuing mitotic instability of the repeat throughout l ife. Repeat length progression does not appear to be indicative of cli nical progression but age probably is. The degree of expansion correla tes with the initial repeat size and 50% of the patients with continui ng expansions showed clinical progression of their disease symptoms ov er the five year study period.