CYP2D6 is essential for metabolism of many compounds that enter the human body. In fact,
25% of all drugs are metabolized by CYP2D6. Population studies have shown that there are SNPs within CYP2D6 that confer ultrarapid metabolism, extensive metabolism, intermediate metabolism, and poor metabolism. Unfortunately, gene duplications can cause individuals to become ultra rapid metabolizers. Downstream enhancers have also been shown to alter CYP2D6 expression. Interestingly, these enhancers have been shown to be quite distant from the actual CYP2D6 gene sequence.
To assess the effect of enhancer duplication on CYP2D6 expression, an in vivo assay could be performed to identify the its impact. A biopsy of liver tissue can be acquired from patients to obtain primary Hepatocytes. These cells should be genotyped to identify wild-type, duplications, and null mutations. Identified patients can then receive a drug that it metabolized by CYP2D6.
Pharmacokinetics assays can then be used to elucidate the functionality of each patient’s CYP2D6 status. Patients with Null mutations should have no functionality, gene duplication patients should have ultrarapid metabolism, and those with wildtype would most likely have a extensive phenotype.
In vitro modeling could be used as well. CRISPR-Cas9 is a great way to add a SNP enhancer or gene duplication. Controls may include wildtype: SNP enhancer and one gene, KO: no gene with SNP enhancer, and CRISPR-Cas9 experimental gene duplication control. Cell lines that can be used are K562, HEK, or another mammalian cell line. Measure metabolites of a selected CYP2D6-metabolized drug in the supernatant. Experimental results should show whether gene duplication caused increased metabolites or decreased. This would be known as an ultrarapid or intermediate/poor metabolizer.
Sadee Wolfgang et al. Common CYP2D6 polymorphisms affecting alternative splicing and transcription: long range haplotypes with two regulatory variants modulate CYP2D6 activity. Human Molecular Genetics Vol. 23 No 1 doi: 10.1093/hmg/ddt417