Phenotype and CTG-repeat size in myotonic dystrophy: A study of 26 patients and 55 relatives

The present multicenter study was carried out to look at genotype-phenotype correlations and CTG-repeat length variations between generations in patie nts with myotonic dystrophy (MD). We investigated 26 patients from 13 unrel ated families and 55 of their relatives from 5 different neurological depar tments, clinically by application of the muscular disability rating score ( MDRS), and the sum of symptoms score (SSS), electromyographically, and by D NA analysis. In MD patients, CTG repeat lengths ranged from 0.2 to 6.4 kb. All patients were heterozygous for the CTG repeats. The MDRS and SSS scores correlated significantly (r = 0.56, r = 0.58, p < 0.05) with the expansion size. Expansion was observed in 4 and retraction in 2 MD families. The exp anded allele was transmitted in all but 2 MD families. In 2 subjects MD cou ld be confirmed solely by DNA analysis. In one patient with clinical featur es of MD, the CTG repeat size was normal.