RAG2 and severe combined immunodeficiency: V(D)J recombination is commenced by enzymes coded by recombination-activating gene (RAG)1 and RAG2, defects which cause failure of the V(D)J recombination initiation process, and consequent failure of T- and B-lymphocyte generation leading to T-B- natural killer (NK)+ severe combined immunodeficiency (SCID), or combined immunodeficiency (CID).