UMs has been described in persons from Saudi Arabia (20%)50 and Ethiopia (16%).51 Pronounced racial-ethnic differences are also observed in the frequencies of CYP2C19 genotypes and phenotypes. PMs are most commonly observed in those of Asian ancestry (~20%), whereas PMs are less frequent in African-Americans (4.5%) and Caucasians (2.3%).48, 49 The significant influence of race-ethnicity was described previously in the context of carbamazepine use and development of severe dermatologic adverse events in HLA-B*1502 carriers in subjects of Asian descent.28 Thus, the magnitude of variability across populations is highly gene and/or polymorphism specific. These examples clearly illustrate the necessity of appropriate test selection in the perspective of the ancestry of the patient.
