BRCA1 and hypoparathyroidism-retardation-dysmorphism syndrome: A deficiency in BRCA1 or BRCA2 within a cell is believed to impair HR repair, termed homologous recombination deficiency (HRD), and place a greater reliance upon alternative DNA repair pathways to repair DSBs, such as non-homologous end joining (NHEJ) and microhomology-mediated end joining (MMEJ) [19].