Second, small-molecule inhibitors of PARP enzymes invoke synthetic lethality in cells in which homologous recombination (HR)-mediated repair is attenuated, a feature that has been exploited in the clinic to selectively kill BRCA1- and BRCA2-mutated cancer cells (Bryant et al., 2005, Farmer et al., 2005). The gene discussed is PARP1; the disease is cancer.