TAP GENE ASSOCIATIONS IN UK CAUCASOIDS

SUMMARY The authors determined the allele frequencies of the TAP1 and TAP2 transporter genes in a healthy UK Caucasoid population by ARMS‐PCR. TAP1A was the most frequent TAP1 allele by far, being present in 76% of subjects. TAP1 alleles could not be assigned in 24% of subjects, since the combinations TAP 1 A/1B and TAP1C/1D cannot be separated. TAP2A was the most frequent TAP2 alleles (75% of subjects) followed by TAP2B (43%), TAP2C (11%), TAP2D (8%) and TAP2E (6%). The authors also identified an individual with a previously undescribed TAP2 allele, TAP2H (isoleucine at amino acid [aa] 379, alanine at aa 565, alanine at aa 665). It was not possible to assign unequivocally TAP2 alleles in 15 individuals (9%) as TAP2A/D and TAP2C/E cannot be distinguished from each other. To address this problem a separate study of families of rheumatoid arthritis (RA) patients selected for this ambiguity were studied. In all five informative families, TAP2A/2D was confirmed as the combination present. In the population studied no evidence was found for linkage disequilibrium between TAP1 and TAP2 or between the TAP genes and HLA‐DP. There was no evidence for extensive linkage disequilibrium between the TAP genes and HLA‐DQ/DR, although TAP2B was associated with DR1 (Δ= 0.056, corrected P < 0.01) and TAP2D with DR4 (Δ= 0.018). In the RA families studied, TAP2D was found on DRB1 *0401 ‐bearing haplotypes.