**Abstract**

The protein tyrosine phosphatase non-receptor type 22 (PTPN22) gene located on chromosomes 1p 13.3–13 encodes a lymphoid-specific tyrosine phosphatase (Lyp) which is involved in autoimmunity by preventing spontaneous T-cell activation and T-cell development and inactivating T-cell receptor-associated kinases and their substrates. Several single nucleotide polymorphisms (SNPs) have been identified in PTPN22, but only one PTPN22 C1858T has been intensively studied in relation to autoimmune diseases. The PTPN22 C1858T functional polymorphism is a strong non-HLA risk factor for several autoimmune diseases and considered to play an important role in etiology of diseases due to significant production of autoantibodies. However, available literature on PTPN22 C1858T polymorphism and autoimmune diseases shows inconsistencies and ethnic variations. Therefore, further genetic studies on patients suffering from various autoimmune diseases from different ethnicities and PTPN22 gene polymorphisms are expected to help better understand the pathogenesis and will contribute to the development of more targeted therapies and biomarkers.

**Keywords:** PTPN22, genetic, polymorphism, autoimmune diseases
