[Prevalence and founder effect of Huntington's disease in the San-in area of Japan]

After the DNA diagnosis, we evaluated the prevalence of Huntington's disease (HD) in the San-in area of Japan, and confirmed the founder effect. The population of the area was 1,387,000 on October 1st, 1993. There were 10 patients with HD in the San-in area, who were diagnosed clinically. They all had involuntary movement, mental disturbance, changes of character and atrophy of the caudate nucleus. However, one of the patients showed no positive family history of HD. The other nine patients had members with HD in their families, although those family members of the patients had already died. The expansion of the CAG repeat was observed in nine of the patients. In the patient who had no positive family history, expansion of the CAG repeat was not seen. According to the nine patients with expansion of the CAG repeat, the prevalence was 0.65/100,000. Haplotypes using polymorphism markers of D4S111 and D4 S136 were studied. The haplotypes which were observed in only 2.7% of the normal population were shown in all nine HD patients. Thus, the obvious disequilibrium was seen. These results suggested a common ancestor of these HD patients.