When natural mutants do not fit our expectations: the intriguing case of patients with XRCC 4 mutations revealed by whole‐exome sequencing

Mutations in the XRCC 4 gene have been recently identified through whole‐exome sequencing (WES). While the overall clinical presentation of the patients (severe short stature, microcephaly, gonadal failure) generally conforms with what is expected for the defect of a critical non‐homologous end‐joining ( NHEJ ) DNA repair factor, the absence of consequence on the proper development of the immune system is rather surprising, given the role of NHEJ in V(D)J recombination. Several hypotheses can be envisioned to explain this discrepancy. Overall, these findings highlight the power of WES in identifying new molecular causes for human diseases while providing with new exciting scientific question to address.