CNVs of the CYP2D6 gene CYP2D6 belongs to the cytochrome P450 system responsible for the metabolism of many commonly prescribed medications (22, 23) . The CYP2D6 gene is highly polymorphic and this can significantly influence the metabolic activity of the enzyme it codes for (debrisoquine 4-hydroxylase) and the therapeutic efficacy of the drugs. Therefore, the pharmacogenetic polymorphism information of this gene would be of great clinical importance in therapeutic decision-making (24) (25) (26) (27) . More than 100 alleles of the CYP2D6 gene have been identified (http://www.cypalleles. ki.se/cyp2d6.htm). Allele-associated variations in the activity of the CYP2D6 enzyme have been observed and individuals carrying these alleles are classified into poor, intermediate, extensive and ultrarapid metabolizers (28, 29) .