ERAP1 and psoriatic arthritis: Interestingly, it was also reported that the ERAP1 gene haplotypes (rs30187) are only associated with psoriatic arthritis in patients with the HLA-B∗27 susceptibility locus, while ERAP1 haplotypes (rs27524, rs26653, and rs30187) also affects psoriasis susceptibility, but only in individuals with the HLA-C risk allele (Strange et al., 2010; Lysell et al., 2013; Kenna et al., 2015; Popa et al., 2016).