Analysis of CAG and CCG repeats in Huntingtin gene among HD patients and normal populations of India

We have analysed the distribution of CAG and adjacent polymorphic CCC repea ts in the Huntingtin gene in 28 clinically diagnosed unrelated Huntington's disease (HD) patients and in normal individuals belonging to different eth nic groups of India. The range of expanded CAG repeats in HD patients varie d from 41 to 56 repeats, whereas in normal individuals this number varied b etween 11 and 31 repeats. We identified six CCC alleles from a total of 380 normal chromosomes that were pooled across different ethnic populations of India. There were two predominant alleles: (CCG)(7) (72.6%) and (CCC)(10) (20%). We report here for the first time one four-repeat CCC allele which h as not been found in any population so far. We found 30 haplotypes (two loc i CAG-CCG) for 380 normal chromosomes. In the present study, no statistical ly significant preponderance of expanded HD alleles was found on either (CC G)(7) or (CCG)(10) backgrounds. Our studies suggest that the overall preval ence of HD in Indian populations may not be as high as in Western populatio ns. Further studies are necessary to identify the origin of HD mutation in these populations.