Impact of CYP2D6 Polymorphism on Steady-State Plasma Levels of Risperidone and 9-Hydroxyrisperidone in Thai Children and Adolescents with Autism Spectrum Disorder.

Objective: The purpose of this study was to investigate the influence of CYP2D6 gene polymorphisms on plasma concentrations of risperidone and its metabolite in Thai children and adolescents with autism spectrum disorder (ASD).

Methods: All 97 autism spectrum disorder patients included in this study had been receiving risperidone at least for 1 month. The CYP2D6 genotypes were determined by real-time polymerase chain reaction (PCR)-based allelic discrimination for CYP2D6*4, *10, and *41 alleles. Plasma concentrations of risperidone and 9-hydroxyrisperidone were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Results: Among the 97 patients, the most important nonfunctional alleles (CYP2D6*4 and *5) were detected, whereas the most common allele was CYP2D6*10 (55.9%). CYP2D6 genotyping revealed 90 (92.78%) patients to be extensive metabolizers (EM) and 7 (7.22%) to be intermediate metabolizers (IM). Plasma levels of risperidone were significantly higher in individuals with CYP2D6*5/*10 (p = 0.02), CYP2D6*10/*10 (p = 0.04), and CYP2D6*10/*41 (p = 0.04). Additionally, the plasma concentration of risperidone/9-OH risperidone ratio in patients with a CYP2D6 activity score of 0.5 were significantly higher than those with a CYP2D6 activity score of 2 (p = 0.04). Conversely, no significant influence was found among CYP2D6 polymorphisms, plasma concentrations of 9-hydroxyrisperidone, and the total active moiety.

Conclusions: This is the first study to investigate the effects of CYP2D6 genetic polymorphisms on the plasma concentrations of risperidone in Thai children with ASD. The findings indicate that CYP2D6 polymorphisms affect the plasma concentrations of risperidone and the risperidone/9-hydroxyrisperidone ratio. Genetic screening for CYP2D6 polymorphisms could help to predict unexpected adverse events caused by the higher plasma concentration of risperidone.