Additions to the myotonic dystrophy linkage group.

One hundred and thirty members of a family with 33 cases of Dystrophia myotonica (Dm) were tested for various genetic markers including Km, Jk, Lu and Se. All individuals tested were Lua negative, but many were heterozygous for the other markers. Except for two cases all patients with Dm were positive for Km3 and Jka and they were secretors. Assuming the genes are linked and that the order of the loci is Km, Jk, Lu, Se, Dm, then there were 22 meioses informative for Dm and in 10 of these a recombination must have occurred between two of the five loci. Looking at individual pairs of loci, there were no recombinations between Km and Jk in seven informative meioses, three recombinations out of 10 meioses informative for Jk/Se, no recombinations between Se and Dm in five informative meioses and three recombinations out of 12 meioses informative for Jk/Dm.