Variability in TRBV haplotype frequency and composition in Caucasian, African American, Western African and Chinese...

The polymorphic T-cell receptor Vbeta (TRBV) genes encode much of the variable region of the T-cell receptor beta chain. Analysis of allele frequencies of three closely linked polymorphic TRBV genes, TRBV7-3, TRBV9 and TRBV6-4, was undertaken in several populations. The frequencies of these alleles are not significantly different in populations of Caucasians, African Americans and Western Africans. However, Chinese population is extremely homogenous at all three loci. The current study identifies the existence of haplotypic relationships between alleles of these genes in the Caucasian population. The ORF allele TRBV7-3*A3 is found exclusively on chromosomes bearing TRBV9*A2 and TRBV6-4*A2 in this cohort. In contrast, TRBV7-3*A1 and the null allele TRBV7-3*A2 are associated only with TRBV9*A1 and TRBV6-4*A1. This pattern of linkage disequilibrium (LD) is altered in the African American and Western African populations. In these cohorts, there is a marked reduction in LD between alleles of TRBV7-3 and TRBV9. This study is consistent with previous population genetic studies wherein African-derived samples have a greater level of genetic diversity compared to Caucasians. These data also demonstrate that patterns of LD are not consistent across the entire TRBV locus.