RAG2 and microcephaly: Within the 22 T-B-NK+ SCID patients, ten (46%) were found to carry homozygous mutations in RAG1 or RAG2, and six (27%) in DCLRE1C. The remaining six patients (27%) had no detectable mutation in the coding regions of RAG1, RAG2, or DCLRE1C. None of those patients were tested for radiosensitivity to exclude the recently described causes of T-B-NK+ SCID such as Cernunnos [39] or DNA-PK deficiency [40]; the lack of growth retardation and microcephaly, however, argues against Cernunnos deficiency but does not exclusively rule out the involvement of either of these 2 genes.