THE INTERLEUKIN-2 RECEPTOR GAMMA-CHAIN MAPS TO XQ13.1 AND IS MUTATED IN X-LINKED SEVERE COMBINED IMMUNODEFICIENCY, SCIDX1

The gene encoding the gamma chain of the lymphocyte interleukin-2 rece ptor has been cloned and shown to be required to associate with the be ta chain in order for L-2 internalization and cell activation to occur (1). We considered this gene, IL2RG, a candidate for the X-linked for m of severe combined immunodeficiency at the SCIDX1 locus, in which af fected males have impaired lymphocyte development. Using fluorescence in situ hybridization and PCR amplification of somatic cell hybrid DNA s, we mapped IL2RG to human Xq13.1, a location within the SCIDX1 criti cal region established by linkage analysis. The 4.2 kb IL2RG gene was sequenced, and its genomic organization was elucidated. Seven of 19 tr ansformed B-lymphocyte cell lines with independent SCIDX1 mutations ha d absent or minimal IL2RG mRNA. Unique point mutations were documented to be specifically associated with the disease and the carrier state in four unrelated affected males and their family members: one in a bo y with no detectable IL2RG mRNA, in which the mutation ablated a splic e donor site; one causing premature chain termination; and two causing distinct amino acid changes. The demonstration of impaired IL2RG mRNA expression in males with X-linked SCID and of unique point mutations in SCIDX1 pedigrees constitutes powerful evidence that the SCIDX1 gene is IL2RG. Noguchi et al. (2) have independently published IL2RG mappi ng to Xq13 and discovery of mutations in three affected males. The spe cific pathogenesis of IL2RG mutations and approaches to gene therapy c an now be addressed in the X-linked form of SCID.