[DNA diagnosis in myotonic dystrophy]

Myotonic dystrophy (DM) is an autosomal-dominant, multisystemic disorder characterized by myotonia, progressive muscle atrophy and weakness, cardiac conduction defect, mental retardation, and cataracts. The phenotypic expression of DM varies from asymptomatic adults to severely affected neonates with congenital DM (CDM). DM shows genetic anticipation, an increase in disease severity and earlier age of onset in successive generations. The molecular basis of DM mutation is an unstable trinucleotide (CTG) repeat located in the 3' end of a transcript that encodes a myotonin-protein kinase. Normal populations have 5 to about 30 CTG repeats, where DM patients have 50-2,000 such repeats. The CTG repeat number is expanded in DM patients when transmitted from parent to child severity. An approximate correlation has been demonstrated between the degree of CTG repeat expansion and clinical severity. The largest repeat sizes are disclosed in CDM. Furthermore, we presented haplotype analysis of CDM families and disclosed localization of myotonic dystrophy protein kinase in DM muscle. DM kinase mRNA was decreased in various tissues of CDM patient.