Features of the type of inheritance of myotonic dystrophy

: The characteristic features of the genetics of myotonic dystrophy (MD) in the Bulgarian population were studied. Seventy-nine pedigrees were analyzed, comprising a total of 119 patients with MD. The following characteristic features of the MD genetics were revealed: (1) Different families exhibited different patterns of the disease transmission, including vertical (as in the autosomal dominant mode of inheritance), horizontal (as in the autosomal recessive mode of inheritance), and mixed (the horizontal transmission for the first generations and the vertical transmission for the subsequent ones); (2) All studied pedigrees were traced back to clinically healthy ancestors; (3) The symptoms of MD exhibited in anticipation, as well as a clinical heterogeneity in sibships with respect to the severity of the disease. The characteristic features of the revealed mode of inheritance may be explained by dynamic mutations.