RAG1 and Immunodeficiency: In particular, while null mutations cause a severe block in T and B cell development (T− B− SCID), hypomorphic Rag1 and Rag2 mutations may cause a spectrum of phenotypes, including OS, atypical SCID, combined immune deficiency with expansion of TCRαβ+ T cells, and combined immune deficiency with granuloma and/or autoimmunity (CID-G/A) despite their common molecular mechanisms underlying the disease (19–25).