Analysis of CCG repeats in Huntingtin gene among HD patients and normal populations in Japan.

Background: Huntington's disease (HD) is a hereditary autosomal dominant neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. The molecular basis of the disease is the expansion of the trinucleotide CAG in the first exon of a gene on chromosome four (4p 16.3). There is another triplet sequence, a CCG repeat, immediately 3' adjacent to the CAG repeat in Huntingtin. This triplet sequence is also polymorphic, alleles of 7 or 10 repeats are predominant in populations, and strong linkage disequilibrium between the CCG (7) allele and HD has been shown in western HD chromosomes, whereas Japanese HD chromosomes strongly associate with an allele of (CCG)10.

Methods: Distribution of CAG and the CCG repeats in Huntingtin in 15 patients with HD living in southern Japan were selected to evaluate the regional difference in the CCG repeat number in Japan.

Results: Among our 15 HD patients, only 4 patients had the (CCG)7 allele, and the (CCG)10 alleles were found in the remaining 11 patients.

Conclusions: In this study, a linkage disequilibrium was found between Japanese HD chromosomes and (CCG)10, whereas western HD chromosomes are strongly associated with (CCG)7. These data suggest that (CCG)10 allele is dominant in southern Japan.