Genealogical study of myotonic dystrophy in Istria (Croatia)

High prevalence of myotonic dystrophy (DM) of 18.1 per 100,000 has been found in Croatian region Istria, a region where a great mixture of nations occurred over the last three centuries. The objective of this study was to test the hypothesis of common ancestry in Istrian DM families. Pedigrees were constructed on the basis of extensive family history obtained from the patients in all Istrian DM families. Church records were consulted in order to improve genealogical reconstruction. Additionally, we performed haplotype analyses with two intragenic and three extragenic DNA polymorphic markers. A common ancestor couple for three of nine nucleus families was found eight generations backward, which was supported by haplotype analysis. In spite of finding an evidence of common ancestry in Croatian Istria we argue that the phenomenon of founder effect is not sufficient to explain the high DM prevalence in Istria.