The Association for Molecular Pathology (AMP) has recently published recommendations outlining cytochrome P450 2C19 (CYP2C19) genotyping. CYP2C19 is involved in the metabolism of many common drugs, which is why AMP’s Pharmacogenetics (PGx) Working Group wanted to define key points for clinical testing. “The purpose of this guideline is to aid clinical lab professionals when designing and validating clinical CYP2C19 genotyping assays, and to promote the standardization of testing across different laboratories,” says Victoria Pratt, first author of the recommendations, Associate Professor of Medical and Molecular Genetics at Indiana University School of Medical, and AMP PGx Working Group Chair. “As with all of our AMP guidelines, we base our recommendations on the evidence that has been published at the time, and what the evidence indicates is necessary to improve professional pharmacogenetics practice and patient care.”
How will the recommendations affect existing assay workflows? They outline a two-tier system to improve validity of CYP2C19 assays, using criteria such as function, population frequency, and reference material availability. Tier 1 includes a minimum set of alleles that are recommended for CYP2C19 PGx tests; tier 2 expands the list to incorporate optional additional alleles.
If your laboratory already performs these tests, you’re likely to be compliant with the recommendations already. “Based on reviewing the commonly available platforms, as well as proficiency data, we believe that most laboratories are already testing for CYP2C19*2, CYP2C19*3, and CYP2C19*17,” Pratt says. “Given that, we do not expect these recommendations to have a large effect on pathologists’ workflows.”
The new document contains recommendations rather than legal requirements, but AMP nevertheless strongly encourages laboratories to follow them. Pharmacogenetics is a rapidly changing field and the complex nature of clinical PGx testing and interpretation mean that we need standardization to deliver the best possible patient care. Pratt assures us that AMP is already on the case. “The AMP PGx Working Group will continually assess new evidence as it accumulates, consider new testing technologies as they emerge and update these recommendations as needed,” she says.
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