A MOLECULAR PROTOCOL FOR DIAGNOSING MYOTONIC-DYSTROPHY

Myotonic dystrophy (DM) is an autosomal dominant genetic disease cause d by an unstable CTG repeat sequence in the 3' untranslated region of the myotonin protein kinase gene. The CTG repeat is present 5-30 times in the normal population, whereas DM patients have CTG expansions of 50 to several thousand repeats. The age of onset of the disorder and t he severity of the phenotype is roughly correlated with the size of th e CTG expansion. We developed a molecular protocol for the diagnosis o f DM based on an initial polymerase chain reaction screen to detect no rmal-sized alleles and small expansions, followed by an improved South ern protocol to detect larger expansions.