For patients with mental health conditions, genetic testing may soon help physicians select the right drug

U of A researcher Katherine Aitchison. Photo: Momentum Magazine.

While prescription antidepressants and antipsychotics have helped millions lead happier and more productive lives, for many, they aren’t effective. 

Adverse reactions and side effects are primary reasons. 

University of Alberta researcher Katherine Aitchison, professor of psychiatry and associate director of mental health in the Neuroscience and Mental Health Institute, is part of a team studying how genetic makeup influences our response to psychiatric drugs.

“Just as our genes determine our hair and eye colour, they can determine how our bodies respond to medicine,” says Aitchison, who is also a member of the Women and Children's Health Research Institute.

“Pharmacogenomics is the study of how a person's unique genetic makeup influences their response to medications. Our goal is to guide prescribing and help doctors select the drugs and doses best suited for each person.”

Certain enzymes in our liver can chemically change drugs. Sometimes chemical changes can make the drugs more — or less — active in the body. Even small differences in the genes for these liver enzymes can have a big impact on a drug’s safety or effectiveness.

Aitchison’s team has developed a robust method of genetic testing for the four enzymes most relevant for psychiatric drugs. People who have mutations in these enzymes can experience adverse drug reactions, but if those mutations are identified, physicians can prescribe a different medication instead.

Her team is now offering testing for these genes in a pilot study for Albertans with treatment-resistant mood disorders.

Pharmacogenomic testing for psychiatric medications is not yet offered by Alberta Health Services.

“For most patients, being prescribed an antidepressant means working with their physician to select one and then using a potentially long trial-and-error approach with the possibility of serious side effects along the way. The likelihood of the first antidepressant working for someone is about 50 per cent — no better than tossing a coin,” says Aitchison.

“If pharmacogenomic testing can be used before or during the medication selection process, we can help shorten the time it takes to find a drug and dosage that work.”

Pharmacogenetic testing has been shown to be accurate and cost-effective in randomized trials. Before it can be made available to the public, comprehensive and robust testing for a greater range of genes must be developed. Doctors, pharmacists and other health-care professionals must be educated on best practices and guidelines must be approved.

Aitchison’s work is one step closer to making that a reality.

“For populations in which we do not have much prior genetic data, such as Indigenous populations, it will be necessary to sequence the DNA. This is quite time-consuming and costly. So we are also working on developing more efficient methods to sequence DNA,” says Aitchison.

“Our long-term goal is to have cost-efficient testing available through Alberta Health Services that is accessible and leaves no one behind.”