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Analysis of haplotypes based on multiple single-nucleotide polymorphisms (SNP) is becoming common for both candidate gene and fine-mapping studies. Before embarking on studies of haplotypes from genetically distinct populations, however, it is important to consider variation both in linkage disequilibrium (LD) and in haplotype frequencies within and across populations, as both vary. Such diversity will influence the choice of "tagging" SNPs for candidate gene or whole-genome association studies because some markers will not be polymorphic in all samples and some haplotypes will be poorly represented or completely absent. Here we analyze 11 genes, originally chosen as candidate genes for oral clefts, where multiple markers were genotyped on individuals from four populations. Estimated haplotype frequencies, measures of pairwise LD, and genetic diversity were computed for 135 European-Americans, 57 Chinese-Singaporeans, 45 Malay-Singaporeans, and 46 Indian-Singaporeans. Patterns of pairwise LD were compared across these four populations and haplotype frequencies were used to assess genetic variation. Although these populations are fairly similar in allele frequencies and overall patterns of LD, both haplotype frequencies and genetic diversity varied significantly across populations. Such haplotype diversity has implications for designing studies of association involving samples from genetically distinct populations.

The development of an effective human immunodeficiency virus type 1 (HIV-1) vaccine is likely to depend on knowledge of circulating variants of genes other than the commonly sequenced gag and env genes. In addition, full-genome data are particularly limited for HIV-1 subtype C, currently the most commonly transmitted subtype in India and worldwide. Likewise, little is known about sequence variation of HIV-1 in India, the country facing the largest burden of HIV worldwide. Therefore, the objective of this study was to clone and characterize the complete genome of HIV-1 from seroconverters infected with subtype C variants in India. Cocultured HIV-1 isolates were obtained from six seroincident individuals from Pune, India, and virtually full-length HIV-1 genomes were amplified, cloned, and sequenced from each. Sequence analysis revealed that five of the six genomes were of subtype C, while one was a mosaic of subtypes A and C, with multiple breakpoints in env, nef, and the 3' long terminal repeat as determined by both maximal chi2 analysis and phylogenetic bootstrapping. Sequences were compared for preservation of known cytotoxic T lymphocyte (CTL) epitopes. Compared with those of the HIV-1LAI sequence, 38% of well-defined CTL epitopes were identical. The proportion of nonconservative substitutions for Env, at 61%, was higher (P < 0.001) than those for Gag (24%), Pol (18%), and Nef (32%). Therefore, characterized CTL epitopes demonstrated substantial differences from subtype B laboratory strains, which were most pronounced in Env. Because these clones were obtained from Indian seroconverters, they are likely to facilitate vaccine-related efforts in India by providing potential antigens for vaccine candidates as well as for assays of vaccine responsiveness.