RAG2 and severe combined immunodeficiency: Mutations causing TnegBneg SCID most often affect genes that play a role in the rearrangement of the B cell receptor (BCR) and T cell receptor (TCR) loci, such as recombination activating genes (RAG) RAG1 and RAG2, DCLRE1C, and PRKDC (Dvorak and Cowan, 2010).