Polymorphic SVA retrotransposons at four loci and their association with classical HLA class I alleles in Japanese, Caucasians and African Americans

Abstract

Polymorphic insertion frequencies of the retrotransposons known as the "SVA" elements were investigated at four loci in the MHC class I genomic region to determine their allele and haplotype frequencies and associations with the HLA-A, -B or -C genes for 100 Japanese, 100 African Americans, 174 Australian Caucasians and 66 reference cell lines obtained from different ethnic groups. The SVA insertions representing different subfamily members varied in frequency between none for SVA-HF in Japanese and 65% for SVA-HB in Caucasians or African Americans with significant differences in frequencies between the three populations at least at three loci. The SVA loci were in Hardy-Weinberg equilibrium except for the SVA-HA locus which deviated significantly in African Americans and Caucasians possibly because of a genomic deletion of this locus in individuals with the HLA-A*24 allele. Strong linkage disequilibria and high percentage associations between the human leucocyte antigen (HLA) class I gene alleles and some of the SVA insertions were detected in all three populations in spite of significant frequency differences for the SVA and HLA class I alleles between the three populations. The highest percentage associations (>86%) were between SVA-HB and HLA-B*08, -B*27, -B*37 to -B*41, -B*52 and -B*53; SVA-HC and HLA-B*07; SVA-HA and HLA-A*03, -A*11 and -A*30; and SVA-HF and HLA-A*03 and HLA-B*47. From pairwise associations in the three populations and the homozygous cell line results, it was possible to deduce the SVA and HLA class I allelic combinations (haplotypes), population differences and the identity by descent of several common HLA-A allelic lineages.