A Narrative Review on Pharmacogenomics in Psychiatry: Scientific Definitions, Principles, and Practical Resources

Pharmacogenetics (PGx) studies the genetic factors underlying interindividual variability in drug response. Only a few countries around the world are already using PGx testing in psychiatric clinical practice, whereas others are still far from adopting it. The main barrier to the clinical adoption of PGx testing seems to be the limited knowledge among psychiatrists regarding the clinical relevance of specific genetic variants to personalize therapies and the accessibility of PGx data. This review aims at further highlighting the importance of PGx-driven clinical decision making for psychotropic medications and raising psychiatrists' awareness of the value of PGx testing in psychiatry.

We summarize the genes for which substantial evidence exists about the clinical utility of integrating their PGx testing in psychiatry. Specifically, we systematically describe the functional role of clinically relevant allelic variants, their frequency across different ethnic groups, and how they contribute to classify patients in relation to their capability in metabolizing psychotropic drugs.

Briefly, clinical guidelines recommend considering PGx testing of the cytochrome class 2 C9 (CYP2C9), C19 (CYP2C19), and D6 (CYP2D6) genes and the human leukocyte antigen (HLA)-A and -B genes for several psychotropic drugs.

Extensive studies have been carried out to provide a solid rationale for the inclusion of PGx testing in psychiatry. Comprehensive clinical guidelines are readily accessible to support health care providers in tailoring the prescription of psychotropic drugs based on patient's genotype information. This approach presents a tangible opportunity to significantly improve individual responses to psychiatric medications.