Population frequencies of the Triallelic 5HTTLPR in six Ethnicially diverse samples from North America, Southeast Asia, and Africa.

Genetic differences between populations are potentially an important contributor to health disparities around the globe. As differences in gene frequencies influence study design, it is important to have a thorough understanding of the natural variation of the genetic variant(s) of interest. Along these lines, we characterized the variation of the 5HTTLPR and rs25531 polymorphisms in six samples from North America, Southeast Asia, and Africa (Cameroon) that differ in their racial and ethnic composition. Allele and genotype frequencies were determined for 24,066 participants. Results indicated higher frequencies of the rs25531 G-allele among Black and African populations as compared with White, Hispanic and Asian populations. Further, we observed a greater number of 'extra-long' ('XL') 5HTTLPR alleles than have previously been reported. Extra-long alleles occurred almost entirely among Asian, Black and Non-White Hispanic populations as compared with White and Native American populations where they were completely absent. Lastly, when considered jointly, we observed between sample differences in the genotype frequencies within racial and ethnic populations. Taken together, these data underscore the importance of characterizing the L-G allele to avoid misclassification of participants by genotype and for further studies of the impact XL alleles may have on the transcriptional efficiency of SLC6A4.