**3.17 X-linked severe combined immunodeficiency (SCID-X1)**

X-linked severe combined immunodeficiency (SCID-X1) is caused by the mutations of interleukin-2 receptor subunit gamma (IL2RG) gene. Patients with the disease lack of T cells and natural killer cells, their B cells are functionally impaired; therefore, they are extremely vulnerable to infections (Aiuti & Roncarolo, 2009; Cavazzana-Calvo et al., 2000; Gaspar et al., 2004; Hacein-Bey-Abina et al., 2002, 2010).
