Reply to 'Selective effects of heterozygous protein-truncating variants'. (January 2019) - Cassa, Christopher; Weghorn, Donate; Balick, Daniel; Jordan, Daniel; Nusinow, David; Samocha, Kaitlin; O'Donnell-Luria, Anne; MacArthur, Daniel; Daly, Mark; Beier, David; Sunyaev, Shamil