Occurrence of CYP2D6 Gene Duplication in Hong Kong

The cytochrome P450 CYP2D6 enzyme debrisoquine 4-hydroxylase metabolizes many different type of drugs commonly used in psychopharmacotherapy, such as tri-cyclic antidepressants and neuroleptics (1). The CYP2D6 gene, which encodes for the CYP2D6 enzyme, is part of a cluster on chromosome 22 that includes two to three related pseudogenes (2). Starting at the 59 end of the cluster, there are two nonfunctional pseudogenes termed CYP2D8P and CYP2D7AP (an additional pseudogene, CYP2D7BP, also can be found) followed by the active gene CYP2D6. Several mutated alleles of the CYP2D6 gene have been identified (3) and associated with alter-ations or polymorphisms in the metabolism of debriso-quine and related drugs metabolized by the CYP2D6 enzyme. As a result, CYP2D6 enzymatic activity range