TYK2 and psoriasis: The JAK1/JAK2-dependent process also participates in the phosphorylation of STAT1, which leads to the activation of IFN-α/β.193 The increased expression of STAT1 and STAT3 was also found in psoriatic skin lesions compared to normal skin.194,195 More interestingly, genetic linkage studies have revealed an association between TYK2 mutations and psoriasis susceptibility.196