CYP2C9*59 is assigned uncertain function due to inadequate evidence. CYP2C9*59 was first described in a patient requiring a low daily warfarin dose of 1.5mg (25994031). No variant was observed in VKORC1 or CYP4F2 in this patient and a subsequent in silico study showed destabilization of the interaction with the heme group may cause reduction in catalytic activity in this allele. In vitro studies found CYP2C9*59 demonstrated decreased enzyme activity with multiple substrates (25142737, 25994031, 25884291). Consensus was not achieved among experts and therefore uncertain function was assigned.