B-CELL-NEGATIVE SEVERE COMBINED IMMUNODEFICIENCY ASSOCIATED WITH A COMMON GAMMA-CHAIN MUTATION

Severe combined immunodeficiency (SCID) is caused by a variety of unde rlying defects. Approximately 40% of cases are thought to be of the X- linked type (SCIDX1), which is phenotypically characterised by the abs ence, or very low numbers, of T cells, but normal or even high B cell numbers. The gene responsible for SCIDX1 is that coding for the common gamma chain (gamma(c)), a component of multiple cytokine receptors. M utations in this gene have been demonstrated in a large number of boys affected by typical SCIDX1. We describe a sporadic case of a boy who had SCID with absent B cells and absent T cells, but in whom a mutatio n in the gamma(c) gene has been demonstrated. In the absence of a typi cal X-linked pedigree, the phenotype in this boy suggested an autosoma l recessive form of SCID and the family would usually have been counse lled accordingly. This family raises the question of the true frequenc y of SCIDX1 amongst sporadic male cases of SCID and highlights the nee d to screen these boys for gamma chain mutations.