Almost 45% of SCID owes to a mutation in a gene(IL2-RG) on X-chromosome which encodes a common chain shared by several cytokine receptors, useful for their functionality. This component is referred to as Cγ ,for common gamma chain.[Mutations in this gene result in very low T-lymphocyte and NK-lymphocyte counts, but the B-lymphocyte count is high (a so-called T-, B+, NK-phenotype). Despite the high number of B-lymphocytes, there is no B-lymphocyte function since the T-cells are not able to “help” the B-cells to function . This deficiency is inherited as an X-linked recessive trait. Only males have this type of SCID, but females may carry the gene and have a 1 in 2 chance (50%) of passing it on to each son.[6]
