ASSOCIATION OF CTG REPEATS AND THE 1-KB ALU INSERTION DELETION POLYMORPHISM AT THE MYOTONIN PROTEIN-KINASE GENE IN THE JAPANESE POPULATION SUGGESTS A COMMON EURASIAN ORIGIN OF THE MYOTONIC-DYSTROPHY MUTATION

We have studied linkage disequilibrium between CTG repeats and an Alu insertion/deletion polymorphism at the myotonin protein kinase gene (D MPK) in 102 Japanese families, of which 93 were affected with myotonic dystrophy (DM). All of the affected chromosomes are in complete linka ge disequilibrium with the Alu insertion allele. Among the normal chro mosomes, alleles of CTG repeats 5 and greater than or equal to 17 are exclusively associated with the insertion allele. On the other hand, i ntermediate alleles of 11-16 repeats show a significantly greater asso ciation with the deletion allele. A strikingly similar pattern of link age disequilibrium observed in European populations suggests a common origin of the DM mutation in the Japanese and European populations.