For example, a study on a small cohort of 22 Greek psoriasis patients treated with ustekinumab genotyped 38 variants that had been significantly associated with psoriasis in genome-wide studies, finding that only two SNPs (rs151823 and rs26653 [ERAP1]) showed an association with a good response to ustekinumab. This evidence concerns the gene ERAP1 and psoriasis.