Human CYP2C19*5 allele is located within 10q24.1-q24.3 and is approximately 90 kb in length. This allele, a variant form of the CYP2C19 wild-type allele, encodes cytochrome P450 2C19*5 protein. The CYP2C19*5 allele exhibits a clinically-relevant SNP (c.1297C>T) in exon 9 that results in a R433W coding change in the heme-binding region of the protein. This alteration in protein sequence abolishes the enzymatic activity of the cytochrome P450 2C19*5 protein. [ ]