Rare variants and complex genomic structure of CYP2D6 necessitate careful assessment and interpretation of haplotype and copy number data

Copy number variations (CNVs) play an important role in the level of activity of many enzymes critical to pharmacogenetics (PGx). Novel exon-level deletions and duplications have been reported for at least 201 pharmacogenes. Several of these are Cytochrome P450 genes, which have been extensively studied due to their role in absorption, distribution, metabolism, and excretion (ADME) of many clinical drugs. CYP2D6 alone is involved in the metabolism of 20-25% of prescribed drugs in the US and Europe.