Association study between HLA-A, -B, -C, -DRB1 alleles and Psoriatic arthritis in southern France.

Psoriatic arthritis (PsA) is a type of inflammatory arthritis associated with psoriasis. HLA association studies performed in northern Europe, comparing patients with control populations, have shown that the highest risk for PsA is carried by HLA-C*06, HLA-B*57 and HLA-B*27 alleles. This retrospective association study compared HLA-A, -B, -C, and -DR alleles of 500 patients from southern France, who fulfilled the CASPAR criteria for Psoriatic Arthritis (PsA), with 2346 controls from healthy blood donors, using the chi-square test. We classified PsA patients into three different subgroups according to disease: purely axial, purely peripheral and combined axial and peripheral. The 'axial' subgroup was associated with HLA-B*27 (OR = 16.3, p = 2.7 × 10-28) and its haplotypes: HLA- B*27-C*01 (OR = 12.4, p = 1.7 × 10-12) and HLA-B*27-C*02 (OR = 8.7, p = 10 × 10-9). The 'axial and peripheral' and the 'peripheral' subgroups were associated with HLA-C*06 (respectively OR = 1.5, p = 3.6 × 10-10 and OR = 2.4, p = 3.6 × 10-12) and its haplotypes HLA-C*06-B*13 (respectively OR = 2.4, p = 1.2 × 10-6 and OR = 2.8, p = 6.4 × 10-11). This association study on a southern French PsA cohort identifies HLA-C*06 as a marker for peripheral PsA and HLA-B*27 as a marker for purely axial PsA.