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Hervas et al. J Transl Genet Genom 2021;5:278-87 https://dx.doi.org/10.20517/jtgg.2021.25 Page 280

[14]
[15]
to methylphenidate have been detected in a sample of 64 children with ASD . A study by Correia et al.
described the influence of genetic variants in the multidrug resistance 1 (MDR1 or ABCB1) gene on clinical
improvement with risperidone therapy in N = 45 ASD patients. Furthermore, associations between
treatment response and polymorphisms in BDNF, HTR2A, serotonin receptor 2C (HTR2C), serotonin
receptor 6 (HTR6), and cytochrome P450 2D6 (CYP2D6) genes were reported in the same study. However,
these findings were not conclusive. Considering the limited number of pharmacogenetic studies in ASD and
the moderate sample sizes, further investigation is required to identify predictors of response that could
improve the efficacy and safety of pharmacological treatments in this population group.

The aim of our study was to identify genetic predictors of drug response in a population group who are
particularly susceptible to adverse reactions. This information may help to improve the efficacy and safety
of pharmacological treatments in children and adolescents with ASD.

METHODS
Study samples
A total of N = 176 children (86% boys and 14% girls, average age = 11.77 ± 4.64 SD) diagnosed with ASD
according to DSM-5 criteria and undergoing pharmacological treatment (N = 146 with methylphenidate
and N = 30 with antipsychotic, antidepressant, anxiolytics, and mood stabilizers) for at least 8 weeks were
included in the study. Treatment response was assessed using the Aberrant Behaviour checklist, (ABC-CV,
Aman et al., 1985), Autism Treatment Evaluation Checklist (Rimland & Edelson, 1999), Clinical Global
Impression-Severity (CGI-S) for autism symptoms, Conners Rating Scale-Revised for parents and teachers
for the assessment of ADHD symptoms (Conners, 1997), Child Behaviour Check list for parents, and
Teacher’s Report Form for teachers to assess general child psychopathology symptoms. Response to
pharmacological treatment was assessed retrospectively from the parents’ CGI categorical scores (0 = poor
response, 1 = some response, 2 = good response, 3 = very good response). Global side effects were assessed
with a score between 0 and 3 (0 = no side effects, 1 = mild side effects lasting less than two weeks, 2 =
moderate side effects lasting more than 2 weeks, 3 = bad side effects with long lasting side effects of more
than a month of duration or intolerable side effects resulting in suppression of medication). Specific
information on the presence or absence of aggression, shutdowns, irritability, mood alterations, and
somnolence were obtained via parents’ interviews. This sample has a statistical power ≥ 85% to detect
moderate effect sizes (f ≥ 0.25, α = 0.05). This project was approved by the Ethics committee of the Hospital
Universitari Mutua Terrassa. Informed consent was obtained from all participants or their legal carers prior
to introduction in the study.

Genetic characterisation
Selected candidates included genes coding for dopaminergic and serotonergic drug targets (SLC6A3, DRD2,
DRD3, DRD4, HTR2A, and HTR2C) and other genes previously associated with treatment efficacy and/or
induced side effects (ANKK1, BDNF, COMT, and HTR1A). DNA was extracted from whole blood samples
using a commercial kit (EZNA SQ Blood DNA Kit II, Omega Bio-Tech, USA) and following manufacturers’
instructions. Sixteen single nucleotide polymorphisms (SNPs) and variable number tandem repeats
(VNTRs) within the 10 selected genes were genotyped using iPlex® Gold chemistry and the MassARRAY
platform (CEGEN-PRB2-ISCIII, University of Santiago de Compostela, Spain) for the SNPs and agarose gel
genotyping methods for the VNTRs. Table 1 contains a complete list of the genotyped polymorphisms.
Polymorphisms were selected based on previously reported associations with response to pharmacological
treatment.