Gene-based drug therapy for children and youth treated with psychoactive medications.

Psychoactive medications are increasingly used to treat children and youth with mental health conditions, but individual variations in response highlight the need for precision medicine. Pharmacogenetic (PGx) testing is a key component of precision medicine. The number of commercial pharmacogenetic testing companies promoting PGx, with the promise of achieving individualized and effective treatment of mental health conditions, has grown exponentially in recent years. Scientific evidence supporting the use of PGx to manage mental health conditions is limited, especially for paediatric populations. This practice point outlines steps guiding the use and interpretation of PGx testing for psychoactive medications in clinical settings, along with key supportive resources. Practice guidelines have been developed for variants in pharmacogenes encoding cytochrome P450 drug-metabolizing enzymes (e.g., CYP2C19, CYP2D6, CYP2C9) as one determinant of drug concentrations in blood, which can support both drug choice and dosing strategy for certain anti-psychotics, anti-depressants, and anti-epileptics. Adverse drug reactions to some anti-epileptic drugs (e.g., carbamazepine and phenytoin) have been associated with certain human leukocyte antigen types and variants in DNA polymerase gamma (POLG; valproic acid). Evidence remains limited for genetic variants of drug target proteins, making it challenging to identify patients with altered treatment responses at a therapeutic blood concentration.