Genetic Variants of the Drug-Metabolizing Enzyme CYP2D6 in Puerto Rican Psychiatry Patients: A Preliminary Report and Potential Implications for Breast Cancer Patients‪.‬

CYP2D6, a P450 drug-metabolizing enzyme predominantly expressed in the liver, is involved in the metabolism of up to 25% of current medications (1-3), many of which are antidepressants and antipsychotics. Moreover, because CYP2D6 has more than 70 known alleles, it is an important major source of interethnic variability and causes a wide range of activity leading to highly variable drug metabolism. The prevalence of the various CYP2D6 alleles has been studied extensively among the populations of Europe, Asia and Africa (1-3). Nonetheless, relatively little information has been obtained from Central and South America, and none from Caribbean nations. Four CYP2D6 phenotypes have been recognized concerning their capacity to metabolize these drugs (1-2) these are: 1) ultra-rapid metabolizer, UM, with at least 3 functional gene copies; 2) extensive metabolizer, EM, with normal (wild-type) activity; 3) intermediate metabolizer, IM, with combinations of active and inactive or reduced activity alleles, and 4) poor metabolizer, PM, when both alleles are inactive. The frequency of the EM phenotype in European Caucasian populations is estimated at 65-80%, IM is 10-15%, PM is 5-10% and UM is 1-5 % (2). The UM phenotype is most prevalent in Ethiopia, 29% (4), and Saudi Arabia, 21% (5), and elevated around the Mediterranean rim, with a 10% prevalence in northern Spain (6). Individuals with the extreme genotypes, PM and UM, are potentially at increased risk for problems with CYP2D6 substrate drugs.