Myotonic dystrophy is a frequent neuromuscular disease with an incidence of 1 : 8000. It is an autosomal dominant disease characterized mainly by muscular weakness and myotonia. The disease is caused by a CTG triplet expansion in a 3’untranslated region of the protein-kinase gene. The authors present their experience with DNA-diagnostics of myotonic dystrophy using the polymerase chain reaction method. On the example of two examined families (eight persons) diagnostic possibilities of the method-in-use in affected families are demonstrated. It is a confirmation of myotonic dystrophy on the basis of absence of one normal (unexpanded) parental allele and exclusion of myotonic dystrophy giving evidence of heterozygosity (two alleles) up to 40 CTG triplet repeats.

        Key words: myotonic dystrophy, polymerase chain reaction