CYP2C9*58 is assigned uncertain function due to inadequate evidence. CYP2C9*58 was first described in a patient requiring a low weekly warfarin dose of 9mg (25075423). No variant was observed in VKORC1 or CYP4F2 in this patient and a subsequent in silico study showed changes in hydrogen bonding which may affect the secondary structure of the protein. In vitro studies found CYP2C9*58 demonstrated decreased enzyme activity with multiple substrates (25142737, 25075423, 25884291). Consensus was not achieved among experts and therefore uncertain function was assigned.