TYK2 and psoriasis: This is further supported by the therapeutic effect of a TYK2 inhibitor in psoriasis [18], and by observed risk in other infectious disease such as tuberculosis where it has been found that homozygosity for the minor allele (C) of rs34536443 is risk, in line with severe COVID-19, and strongly impairs IL-23 signaling in T cells and IFN-γ production in PBMC [19,20].