Guarneri et al. assessed the frequency of glutathione S-transferase M1/glutathione S-transferase T1(GSTM1/GSTT1) polymorphisms in 148 individuals with psoriasis versus 148 age-matched healthy counterparts, revealing that both glutathione S-transferase T1 null and GSTM1/GSTT1 “double null” genotypes are associated with psoriasis. This evidence concerns the gene GSTM1 and psoriasis.