The severe combined immunodeficiency (SCID) [59] and recombinase 2 gene (Rag2) knockout [60] mice have spontaneous mutations in the prkdc locus or targeted mutation disrupting Rag2 results in a lack of mature T and B cells, respectively. Whereas Beige [61] and perforin 1 gene (pfp) knockout [62] mice have mutations that lead to an impairment of natural killer (NK)-cell function. The gene discussed is PRF1; the disease is severe combined immunodeficiency.