In cells with wild-type BRCA1/2, double-strand breaks are repaired via homologous recombination, but in BRCA1/2-deficient cells with homologous recombination deficiency (HRD), DNA strand breaks rely on PARP1 functionality for repair [94, 95]. Here, BRCA1 is linked to hypoparathyroidism-retardation-dysmorphism syndrome.