The deterimental CYP2C19*4-defining SNP (rs28399504) has been identified to be linked (i.e. on the same chromosome) with *17 (-806C>T; rs12248560) in certain ethnic subpopulations. To distinguish the *4 (no function) and *17 (increased function) alleles, both rs28399504 and rs12248560 needs to be genotyped [PMID: 21358751, PMID: 24012947]). This haplotype is designated CYP2C19*4B [PMID: 21716271, PMID: 21358751].