However, XIAP deficiency underlying a primary immunodeficiency disorder was not described until 2006, when Rigaud et al. (2) found pathogenic variants in XIAP in male patients from 3 families with X-linked lymphoproliferative syndrome (XLP) phenotypes who lacked SH2D1A mutations. The gene discussed is SH2D1A; the disease is X-linked lymphoproliferative disease.