The association of ERAP1 and ERAP2 single nucleotide polymorphisms and their haplotypes with psoriasis vulgaris is dependent on the presence or absence of the HLA-C*06:02 allele and age at disease onset.
In addition to HLA-A*02:07 and HLA-C*06:02, stepwise conditional analysis identified an independent PsV risk of HLA-DQβ1 Asp57 (odds ratio = 2.19, P = 1.9 × 10<sup>-6</sup>).
Stepwise analysis revealed multiple HLA-C(∗)06:02-independent risk variants in both class I and class II HLA genes for PsV susceptibility (HLA-C(∗)12:03, HLA-B amino acid positions 67 and 9, HLA-A amino acid position 95, and HLA-DQα1 amino acid position 53; p < 5.0 × 10(-8)), but no apparent risk conferred by MICA.
Susceptibility to psoriasis vulgaris in our study group is significantly associated with HLA-C*06 (odds ratio (OR) = 3.85), DRB1*07 (OR = 2.56) and DQB1*02 (OR = 1.09), respectively, whereas DRB*01 (OR = 0.05) is associated negatively.
Using a candidate gene approach, genes robustly confirmed to be associated with psoriasis vulgaris (PsV) have also been found to be associated with PsA (HLA-Cw*0602, IL23R, IL12B).
For PsA, but not psoriasis vulgaris without joint involvement, a strong association with the allele TNF*-857T (odds ratio 1.956 [95% confidence interval 1.334-2.881]; corrected P = 0.0025) was also detected in patients negative for the PSORS1 risk allele.
With regards to HLA-Cw*0602, its allele frequency was significantly increased in patients with early-onset PV (25.3% vs. 4.8%, P < 10(-7)), but not in patients with PsA.
The HLA-C locus profile of this cohort was studied by methods based on molecular biology and was compared with that of 45 patients with psoriasis vulgaris and 177 healthy blood donors from the same ethnic origin.
PSORS1 is the major susceptibility locus for psoriasis vulgaris (PV) and lies within an approximately 200 kb segment of the major histocompatibility complex on chromosome 6p21.3.
HLA-Cw*0304 (5.07% vs. 14.43%, Pc < 1 x 10(-3)), -DQA1*0501 (5.79% vs. 14.09%, Pc < 0.05) were found to be negatively associated with PV, but HLA-A*2 (2.54% vs. 6.38%, Pc < 0.5) was decreased in PV patients without statistical significance.
Our results show conclusively that psoriasis vulgaris and guttate psoriasis have a similar genetic basis for their association to PSORS1, whereas palmoplantar pustulosis appears to be a distinct disorder.
As serotyping has proved to be less valuable in the determination of HLA-C, genotyping of HLA-C in 68 Taiwanese psoriasis vulgaris (PSV) patients was performed using polymerase chain reaction/sequence-specific oligonucleotide probe hybridization (PCR-SSOPH) of HLA-Cw genes.