Thr175Ala of Toll-like receptor-4 gene is a common non-synonymous single nucleotide polymorphism in a Japanese population

It has been shown that a non-synonymous polymorphism Asp299Gly of Toll-like receptor-4 (TLR-4) gene could be associated with lipopolysaccharide hyporesponsiveness and decreased risk of atherosclerosis in Caucasians. However, this polymorphism is not detected in Asians including Japanese and hence considered to be a population-specific one. To investigate if there are common non-synonymous SNPs of TLR-4 gene in Japanese, 100 DNA samples randomly selected from 613 healthy volunteers were sequenced for exons 2 and 3. As a result, Thr175Ala (A690G) was found in 6 out of 100 samples. Genotyping of Thr175Ala was then performed for 842 DNA samples from 613 healthy volunteers and 229 patients with ulcerative colitis. Frequency of heterozygote (Thr/Ala) or homozygote (Ala/Ala) in healthy subjects was 2.3% (14/613) or 0% (0/613), respectively. There was no significant difference of the genotype distribution between ulcerative colitis patients and age- and gender-matched controls. Furthermore, Thr175 is known to be involved in a potential N-linked glycosylation site and hence the polymorphism might affect the function of TLR-4. These data suggest that Thr175Ala is a common non-synonymous polymorphism of TLR-4 gene in a Japanese population.