Null mutations in RAG1 or RAG2 cause autosomal recessive T– B– NK+ SCID in humans, however hypomorphic mutations in the same genes have been associated with a spectrum of clinical phenotypes, including Omenn syndrome, atypical SCID and combined immune deficiency with granulomas and/or autoimmunity (CID-G/AI) (33). Here, RAG1 is linked to severe combined immunodeficiency.