The cytochrome P450 2D6 (CYP2D6 assay) is an important liver enzyme involved in the metabolism of up to 25% of clinically used drugs (e.g. tamoxifen, opiates, anti-depressives or anti-psychotics). The CYP2D6 gene is highly polymorphic with over 100 allelic variants and numerous sub-variants described in the Human Cytochrom P450 Database (www.cypalleles.ki.se).
While the most frequent allelic variations are caused by single nucleotide polymorphisms (SNPs) and small insertions or deletions, highly homologous regions in the CYP2D6 gene locus facilitate unequal cross-over leading to large deletions, duplications and gene conversions. Most of these alterations result in a change of the CYP2D6 enzyme activity. Guidelines recommend to determine the CYP2D6 genotype of patients prior to medication in order to be able to estimate the metabolic activity of the enzyme, and in consequence the clinical efficacy or even the applicability of defined drugs.
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