Competitive proliferation assay. Wild-type and Y361 mutant BaF3-FPTase β cells were mixed at equal ratio, plated in 12 separate wells, and allowed to proliferate in culture to confluency. Individual wells were harvested and FPTase β was sequenced and compared with time 0 controls. Results are a compilation of the relative number of predominantly mutant wells in 6 independent experiments (“Patients, materials, and methods”). A mutant contribution of 50% would indicate no proliferative advantage. Error bars are standard errors. Bottom: immunoblot of FPTase β in the pure wild-type and mutant cells. FPTase β is a 46-kDa protein. The FPTase β antibody appears as doublet with an additional 50 kDa band.