Race-ethnicity is an important factor that may influence drug response through gene variants and may be observed at different frequencies depending on one’s ancestry.47 Racial-ethnic variation needs to be recognized and taken into the consideration during the selection process of an appropriate genetic test panel. Different racial or ethnic groups may not only vary in the frequency of a given variant identified as important for pharmacogenomic testing but may also carry other, different variants not identified or included in current tests. Generally speaking, CYP2D6 PM status is most commonly observed in Caucasians (~10%), is relatively infrequent in Asians (0–1.2%), and differs widely in African-Americans (ranging from 1.9–7.3%).48, 49 Among American populations, UMs have been observed at similar frequencies in Caucasians and African-Americans (4.3% and 4.9%, respectively).48, 49 UMs are rarely seen in persons of Asian descent. The highest frequency of 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
