CYP2C19*22 is assigned no function based on limited in vitro and computational evidence. An in vitro study found CYP2C19*22 had 8% enzyme activity compared to wildtype with a clopidogrel substrate and nondetectable enzyme activity compared to wildtype with a mephenytoin substrate (25001882). Crystal structure analysis shows the Arg186Pro substitution in CYP2C19*22 disrupts hydrogen bonds and alters protein structure resulting in decreased heme affinity and ultimately enzyme activity (19164093). Therefore, consensus among experts was no function based on limited evidence as it was determined the phenotypes containing this allele would be clinically distinct from phenotypes comprising normal function and decreased function alleles.