The previous studies have shown a reduction in the frequency of NK cells in the peripheral blood in patients with T1D, and a reduced surface expression of the activating receptors NKp30 and NKp46 as well as lower mRNA levels of IFN-γ and perforin in NK cells of patients with long-standing T1D, when compared to controls without T1D [103,104]. This evidence concerns the gene PRF1 and type 1 diabetes mellitus.