XRCC4 and microcephaly: X-ray cross-complementing 1 (XRCC1) and X-ray cross-complementing 4 (XRCC4) are key scaffold proteins that play essential roles in SSBR and DSBR via NHEJ pathway, respectively [2, 3, 24]; the mutation of these proteins also results in inherited diseases with neurodegeneration, growth defect and microcephaly, respectively [3, 25].