Table 1.

Classification of SCID based on the immunophenotype

Defects	Phenotypes in T/B/NK cells	Gene	Heredity	Disease
Defects in cytokine Signaling	T−B+NK−	IL2RG	XL	X-Lined SCID
	T−B+NK−	JAK3	AR
	T−B+NK+	IL7R-A	AR
Defect in V (D) J recombination	T−B−NK+	RAG 1	AR	Omenn Syndrome
	T−B−NK+	RAG 2	AR	Omenn Syndrome
	T−B−NK+	DCLRE1C	AR
Impaired signaling through the pre-T cell receptor	T−B+NK+	CD3D	AR
	T−B+NK+	CD3E	AR
	T−B+NK+	CD3G	AR
Increased lymphocyte apoptosis	T−B+NK+/NK−	PTPRC	AR
	T−B−NK−	ADA	AR	ADA-SCID
	T−B−NK−	AK2	AR	Reticular dysgenesis
Other mechanisms	T−B+NK+	CORO1A	AR
	T−B+NK+	RMRP	AR	Cartilage hair hypoplasia (CHH)

Numerous immunophenotypes have been found in SCID and responsible genes (Adapted from Buckley & Cossu (3, 4)). T: T cell, B: B cell, NK: natural killer cell, AR: Autosomal Recessive, XL: X-Linked.