CYP2C19*39 is assigned uncertain function due to inadequate data. Currently, there is no published evidence describing the function of the CYP2C19*39 allele. One in vitro study for 12718A>C (E122A) determined the metabolic activities towards CEC(3-cyano-7-ethoxycoumarin) O-deethylation and concluded decreased function for this variant (21692664) and another study found the Clint for S-mephenytoin is not significantly different and for omeprazole decreased to 0.27 fold compared to no variant (21325430). Consensus was not achieved among experts as data were sparse and not consistent among substrates. Therefore, uncertain function was assigned.