CTG-repeat length in distal and proximal leg muscles of symptomatic and non-symptomatic patients with myotonic dystrophy: relation to muscle strengthand degree of histopathological abnormalities

Myotonic dystrophy (DM) is an autosomal dominant, multisystemic disorder wi th a variable phenotypic expression including muscle weakness and myotonia. The muscle wasting is most marked in distal limbs and in facial and neck m uscles, although proximal limb muscles become affected as the disease progr esses. The CTG-trinucleotide-repeat expansion associated with myotonic dyst rophy is usually larger in muscle tissue than in leukocytes. It is unclear whether the repeat length itself bears any relation to the differences in t he degree of weakness and atrophy between different muscles. We therefore a nalysed CTG-repeat lengths in blood and in proximal (m. vastus lateralis) a nd distal (n. tibialis anterior) muscles of patients with DM (n = 4) and no n-symptomatic carriers of the mutant DM allele (n = 2) using conventional S outhern blot hybridization. Muscle strength and histopathological abnormali ties were evaluated for each muscle. In patients with clinical symptoms, th e degree of paresis and morphological abnormalities was markedly more prono unced in m. tibialis anterior than in m. vastus lateralis. in these individ uals, the CTG-repeat length was larger in muscles than in leukocytes, n hel eas in the two non-symptomatic carriers no difference could be detected. F urthermore, there was no clear difference in the repeat length between the two muscles in any of the patients. In conclusion, the selective muscular w eakness and atrophy in DM do not seem to be related to differences in CTG-r epeat length between different muscles, Eur J Neurol 6:341-346 (C) 1999 Lip pincott Williams & Wilkins.