Ethnic variation in the clinical expression of idiopathic torsion dystonia.

Although childhood, limb-onset idiopathic torsion dystonia (ITD) is at increased prevalence among Jews, and Ashkenazi Jews with this form of ITD show linkage disequilibrium for a unique haplotype, little else is known about phenotypic or genetic variation in ITD among ethnic groups. We assessed clinical features in 786 ITD patients and determined the relative frequencies of various clinical forms of ITD in the major ethnic groups. Several differences in age-at-onset and site-at-onset distributions among groups were demonstrated. As expected, Ashkenazi Jews had an earlier age-at-onset distribution than did non-Jewish Caucasians. In the early-onset group, Jews were less likely to have cervical onset and more likely to have onset in the limbs than were non-Jewish Caucasians (p < 0.01). Among late-onset cases, Jews had less cervical onset and more cranial onset than did non-Jewish Caucasians (p < 0.01). African-Americans showed suggestive differences in both age at onset and site at onset as compared with the two caucasian groups, with an intermediate age at onset, a deficit of leg onset, and an excess of cranial and larynx onset. Subgroups of non-Jewish Caucasians showed no significant differences from each other. The observed ethnic variations in age at onset and site at onset of ITD suggest population differences in disease-causing alleles or loci. However, environmental influences on expression of ITD can not be excluded.