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 repeats in the Huntingtin gene in 28 clinically diagnosed unrelated Huntington's disease (HD) patients and in normal individuals belonging to different ethnic groups of India. The range of expanded CAG repeats in HD patients varied from 41 to 56 repeats, whereas in normal individuals this number varied between 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 has not been found in any population so far. We found 30 haplotypes (two loci CAG-CCG) for 380 normal chromosomes. In the present study, no statistically significant preponderance of expanded HD alleles was found on either (CCG)(7) or (CCG)(10) backgrounds. Our studies suggest that the overall prevalence of HD in Indian populations may not be as high as in Western populations. Further studies are necessary to identify the origin of HD mutation in these populations.