What is pharmacogenetics?

Pharmacogenetics examines how inherited variants affect the efficacy and tolerability of medicines. The most common mechanism concerns enzymes that break a drug down or first activate it. Anyone producing only limited amounts of such an enzyme has a higher drug concentration at standard doses and therefore a higher risk of side effects. Conversely, a drug that must be activated in the body may simply not work when the enzyme is impaired. Unlike many other genetic statements, pharmacogenetics therefore has a direct practical consequence: a different dose or a different preparation.

For individual gene-drug pairs, very well; across the breadth of all medicines, not at all. The most robust example is DPYD: since April 2020 the European Medicines Agency has recommended testing for DPD deficiency before treatment with fluorouracil, capecitabine, tegafur or flucytosine, because that deficiency leads to severe and sometimes life-threatening side effects. Similarly clear guidance exists for TPMT and NUDT15 before thiopurines and for CYP2C19 with clopidogrel. For the great majority of substances, by contrast, no robust recommendation exists. The shortness of that list is the actual information.

Most of all for three groups. First: people facing one of the affected treatments concretely, above all chemotherapy with fluoropyrimidines or thiopurine therapy. Second: people who did not tolerate a medicine because of side effects without a cause being found, such as muscle symptoms on statins. Third: people on long-term medication where the effect falls short of what was expected. Without one of these reasons, the benefit lies in having the result on file should such a treatment ever arise. That is a legitimate but weaker reason.

A pharmacogenetic profile is part of the genetic analysis and is obtained in the Ultimate program together with whole-genome sequencing. Findings are interpreted medically and documented in writing so that you can pass them to the people running your treatment. That is precisely the point: a pharmacogenetic result only acquires value where a prescription is written, not with us. We do not change ongoing medication; we supply the basis for it to the treating physician. Which procedures sit in which program is set out on the program page.

It cannot predict whether a medicine will help you. It says something about metabolism and tolerability, not about therapeutic success. Nor does it explain all the variation between people: kidney function, liver function, age, weight, co-medication, smoking and adherence often matter more than a variant. And it does not replace clinical observation, because a side effect shows up before a test result explains it. A pharmacogenetic result is therefore an additional factor in a decision that remains a medical one, and never a reason to change medication on your own.