PTPN22 and vitiligo: However, Silverberg reports that both AA and vitiligo share the following susceptibility/risk gene alleles: (1) tyrosine-protein phosphatase nonreceptor 22 (PTPN22), (2) Fas ligand (FASLG), (3) CTLA4, (4) HLA-A, (5) HLA-DRB1/DQA1, (6) IL-2Rα, (7) CD44, (8) IKZF4, and (9) Src-homolog 2B adaptor protein 3 (SH2B3) [93].