Mutations in CIITA and other MHC-II enhanceosome genes cause the bare lymphocyte syndrome (BLS) (Steimle et al, 1993, 1995; Nagarajan et al, 1999; Masternak et al, 1998; Durand et al, 1997; Reith et al, 1988). The gene discussed is CIITA; the disease is MHC class II deficiency.