Genotype Frequency of the Common TLR4 SNPs in a Kurdish Population: Global Reviews and Out-of-African Migrations.

Toll-like receptors (TLRs) are cellular innate immune receptors that explore microbial molecules. For instance, TLR4 can sense bacterial lipopolysaccharides, inducing cytokines and antimicrobial peptides against the bacteria. Single-nucleotide polymorphisms (SNPs) in TLR4 are associated with diseases such as septic shock. Therefore, investigations of common SNPs may help explain the pathogenesis of diseases and various innate immune responses to infections. This study investigated genotypic frequencies of the two common TLR4 SNPs, Asp299Gly and Thr399Ile, in a Kurdish population using restriction length fragment polymorphisms (RFLPs). Global frequencies of both TLR4 SNPs in different populations of sub-Saharan Africa, North Africa, western Asia, Eurasia, and East Asia were also used to infer human migrations and past settlements. The RFLP data demonstrate that, in the Kurdish population, the genotypic frequencies of both SNPs are similar to Iranian or other West Asian populations, which in turn are comparable to Eurasian populations, suggesting past admixture due to migrations, population intermixing, and common ancestry. Globally, the frequencies of the homozygous wild-types of TLR4 variants are prevalent, but homozygous mutants are rare or lacking in almost all global populations. Frequencies of the heterozygotes varied among populations. For instance, in sub-Saharan Africa the frequency of the Asp299Gly SNP is higher than that of Thr399Ile, whereas in the Arabian Peninsula both SNPs are present at high frequencies. In contrast, East Asian populations lack or have very low frequencies of both TLR4 SNPs of interest. Moreover, co-segregation of the TLR4 SNPs is common in some populations, which may indicate important associations with certain diseases. Future studies are required to link the TLR4 SNPs with either resistance or susceptibility to diseases.