The occurrence of torsion dystonia in the Ashkenazi Jewish population as stated by the Department of Epidemiology and Public Health of Yale University School of Medicine in New Haven, CT; "Reports dating to the beginning of this century describe Ashkenazi Jewish (AJ) families with multiple cases of ITD either in siblings (Schwalbe 1908; Bernstein 1912; Abrahamson 1920) or in parents and offspring (Wechsler and Brock 1922; Mankowsky and Czerny 1929; Regensberg 1930). The first comprehensive evaluation of the mode of inheritance of ITD in Jewish and non-Jewish families was described by Zeman and Dyken (1967), who concluded that the disorder was inherited as an autosomal dominant with incomplete penetrance in both populations. Although they concluded that the gene frequency was higher in the AJ population than in non-Jews, no difference in mode of inheritance or disease mechanism was construed."