Two people can take the same dose of the same medicine and have very different results. One may improve, while the other gets little benefit or develops serious side effects. Part of the explanation often lies in their genes.

Pharmacogenomics uses genetic information to predict how someone may respond to certain medicines. Some genes make proteins that help the body process medicines. Others influence how medicines act. Variants in these genes can change how well a treatment works or the risk of side effects.

Genes are only part of the picture. Age, kidney and liver function, other medicines and the condition being treated can all affect a person’s response. Allergic reactions also have different causes.

Almost everyone carries a relevant variant. An analysis of nearly 500,000 UK Biobank participants found that 99.5% were predicted to have an unusual response to at least one drug because of variants in 14 well-studied genes. Almost one-quarter had already been prescribed a medicine affected by one of those genes.

The immediate value of this information is narrower than that figure might suggest. A variant becomes useful when someone is taking, or may be prescribed, a relevant medicine and there is good evidence about what a doctor should do differently.

In those circumstances, testing may prevent harmful reactions or ineffective treatment. Genetic differences account for only a proportion........

© The Conversation