PTPN22 and Autoimmunity: Numerous candidate studies performed in the pre-genomic era further pointed to “PAI-associated genes”, i.e. polymorphisms that are significantly more (un)common in patients than in healthy controls, revealing several “known autoimmunity genes” to also confer risk for PAI, including HLA, CTLA4, BACH2 and PTPN22 (30–34).