PTPN22 and type 1 diabetes mellitus: A genetic association involving a functional polymorphism of the protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene was reported to be associated with rheumatoid factor-positive (RF+) RA, with type 1 diabetes, with systemic lupus erythematosus and with autoimmune thyroid disease [12-19].