Table 1.

Human SCID genotypes

Gene Defect	Defective Protein, Function	% of SCIDa	Lymphoctye Profile
			Tb	B	NK
IL2RG (X-linked)	Common γ-chain (γc) of receptors for IL-2, 4, 7, 9, 15, 21	45- 50%	−	+	−
ADA	Adenosine deaminase	16%	−	−/+	−
IL7R	α chain of IL-7 receptor	9%	−	+	+
JAK3	Janus kinase 3 activated by γc	6%	−	+	−
DCLRE1C	Artemis, T and B cell antigen receptor rearrangement	<5%	−	−	+
RAG1/2	T and B cell antigen receptor rearrangement	<5%	−	−	+
LIG4	DNA ligase IV antigen receptor rejoining	rare	−	+	+
CD45	Protein tyrosine phosphatase receptor (PTPRC), required for T, B activation by antigen	rare	−/low	+	+/low
TCRD, TCRE, TCRZ	CD3 δ, ε, and ζ deficiency with impaired T cell development	rare	−/low	+	+
LCK	Lymphocyte tyrosine kinase p56lck, T cell development and activation	rare	−/low	+	+
FOXN1	Forkhead box N1, thymus and hair follicle development (ortholog of nude mouse)	rare	−/low	+	+
Currently unknown	Unknown, including reticular dysgenesis and congenital anomaly syndromes with SCID	~10%	−/low	+/−	+/−

^aBased on Buckley,¹ Cavazzana-Calvo et al.²⁶ and unpublished estimates (J. Puck).

^bSome patients have substantial numbers of maternally derived T cells at time of diagnosis.