Genotype–phenotype correlation is strong, as null variants of RAG1 and RAG2 genes result in the T-B- severe combined immune deficiency (SCID) phenotype, whereas hypomorphic RAG variants have been associated with distinct clinical entities including Omenn syndrome (OS) and combined immunodeficiency with granuloma and/or autoimmunity (CID/G-AI) with herpesvirus infections and lymphoproliferation (2–5) and with selective polysaccharides antibody deficiency (6). Here, RAG1 is linked to severe combined immunodeficiency.