Type 1 diabetes incidence is due to multiple factors one of the most important factors is genetics, STAT proteins are cytosolic proteins that have a role in the intracellular signaling downstream of the type I and type II cytokine receptors [17–19], former studies and researches showed that type 1 diabetes incidence have been related to different genetic variants among different genes, such as a study on Tunisians showed that a variant of CREM gene, PTPN22, TCRβ, CD3z, ZAP70, and CTLA-4 gene variants correlation with T1D [20–22]. Here, PTPN22 is linked to type 1 diabetes mellitus.