Naturally occurring human genetic variants predicted to cause loss of function of protein-coding genes provide an in vivo model of human gene inactivation that complements cell and model organism knockout studies. Here we investigate the application of human loss-of-function variants to assess genes as candidate drug targets, with three key findings. First, even essential genes, where loss-of-function variants are not tolerated, can be highly successful as targets of inhibitory drugs. Second, in most genes, loss-of-function variants are sufficiently rare that genotype-based ascertainment of homozygous or compound heterozygous “knockout” humans will await sample sizes ~1,000 times those available at present. Third, automated variant annotation and filtering are powerful, but manual curation remains critical for removing artifacts and making biological inferences, and is a prerequisite for recall-by-genotype efforts. Our results provide a roadmap for human “knockout” studies and should guide interpretation of loss-of-function variants in drug development.

Evaluating potential drug targets through human loss-of-function genetic variation