Those groups that used genome-wide CRISPR-Cas9 chemogenetic viability screening identified the Shieldin complex with an elegant experimental set-up in which BRCA1 mutated cancer cell lines or engineered BRCA1 KO cells, were treated with PARPi at a dose with which the majority of cells are killed (Dev et al., 2018; Noordermeer et al., 2018). The gene discussed is BRCA1; the disease is cancer.