The PTPN22 gene is considered to be the most important non-HLA autoimmunity gene, of which the genetic variant rs2476601, 1858 C>T leading to an arginine–tryptophan substitution, is associated with multiple indications of autoimmunity including RA, SLE, and systemic sclerosis. The gene discussed is PTPN22; the disease is systemic sclerosis.