Microcephalin-1 (MCPH1) is a tumour suppressor protein that regulates homologous recombination repair (HRR) and is down-regulated in several tumour types. Given that HRR-defective cancer cells can be killed via synthetic lethal approaches, MCPH1 thus represents an attractive target in cancer therapy. Functionally, cells lacking MCPH1 have reported defects in the recruitment and retention of BRCA2 and RAD51 to DNA double strand breaks (DSBs) during HRR, though the magnitude of this defect in huma...