Psoriasis is a chronic inflammatory disease of the skin. The causes of psoriasis 
are unknown, although family and twin studies have shown genetic factors to play 
a key role in its development. The many genes associated with psoriasis and the 
immune response include TNF α , IL23, and IL12. Advances in knowledge of the 
pathogenesis of psoriasis have enabled the development of new drugs that target 
cytokines (e.g., etanercept, adalimumab, and infliximab, which target TNF α , 
and ustekinumab, which targets the p40 subunit of IL23 and IL12). These drugs 
have improved the safety and efficacy of treatment in comparison with previous 
therapies. However, not all patients respond equally to treatment, possibly 
owing to interindividual genetic variability. In this review, we describe the 
genes associated with psoriasis and the immune response, the biological drugs 
used to treat chronic severe plaque psoriasis, new drugs in phase II and III 
trials, and current knowledge on the implications of pharmacogenomics in 
predicting response to these treatments.