A shared haplotype for dentatorubropallidoluysian atrophy (DRPLA) in Italian families testifies of the recent introduction of the mutation

To clarify the population history of dentatorubropallidoluysian atrophy (DRPLA) in Italy and to date back the introduction of the mutation, we reconstructed extended haplotypes flanking the CAG repeat in 10 patients of Italian ancestry, analyzing their similarity/dissimilarity as a function of distance from the CAG repeat. Our aim was to compare the hypothesis of a single, recent genealogy connecting all the observed haplotypes with the alternative hypothesis of multiple introductions by more distantly related haplotypes from outer sources. Polymorphic DNA markers were chosen to cover a region of 153 kb flanking the CAG repeat, that is, informative for dating the age of the DNA segment unaffected by recombination. In all patients, an expansion of the ATN1 CAG segment was confirmed residing onto the same narrow haplotype described to be associated with the CAG expansion in the Japanese and Portuguese populations. We also observed the disruption of the DRPLA haplotype at longer distances, on both sides of the CAG. Our results are compatible with a single founder in the last 600 years, most likely before the last 270 years. These estimates for the Sicilian population largely overlap a period in which the Japanese haplotype with the DRPLA mutation could have been introduced by the Portuguese maritime travelers.