The authors present their experience with molecular-genetic diagnostics of myotonic dystrophy type 1. The disease is associated with a CTG-triplet expansion in the 3’ non-translated region of the myotonin protein kinase gene. Using an example of a family with two affected members, they demonstrate and compare methods using polymerase chain reaction (PCR), triplet repeat-primed PCR (TP PCR) and restriction fragment length-polymorphism (RFLP). In a four-member family (parents and two daughters) with clinical symptoms of myotonic dystrophy type 1 in the mother and one of the daughters, the above mentioned methods were used to demonstrate CTG-triplet expansion and to determine the approximate sizes of these expansions. A considerable increase of the expansion was found in the affected daughter relative to the mother, in agreement with the more severe clinical affection of the daughter, what is a manifestation of the anticipation phenomenon. Furthermore, CTG triplet repeat counts in alleles without expansion were determined in both affected women and in the healthy father and healthy daughter, as well.

        Key words: myotonic dystrophy, TP PCR, anticipation