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 (16). This evidence concerns the gene RAG1 and combined immunodeficiency.