Allele-specific associations of 5-HTTLPR/rs25531 with ADHD and autism spectrum disorder

Background: The aims of the present study were to examine the association between a common serotonin transporter gene (SLC6A4) polymorphism 5-HTTLPR/rs25531 with severity of attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) symptoms. Methods: Mothers and teachers completed a validated DSM-IV-referenced rating scale for ADHD and ASD symptoms in 118 children with ASD. Results: Analyses indicated that children with at least one copy of the S or L_G allele obtained significantly more severe maternal ratings of hyperactivity (p=0.001; ηp²=0.097) and impulsivity (p=0.027; ηp²=0.044) but not inattention (p=0.061; ηp²=0.032), controlling for ASD severity, than children homozygous for the L_A allele. Conversely, mothers' ratings indicated that children with L_A/L_A genotype had more severe ASD social deficits than S or L_G allele carriers (p=0.003; ηp²=0.081), controlling for ADHD symptom severity. Teachers' ratings though consistent with mothers' ratings of hyperactivity and social deficits were marginally significant (p=0.07/p=0.09). There was some evidence that the magnitude of parent-teacher agreement regarding symptom severity varied as a function of the child's genotype. Conclusion: The 5-HTTLPR/rs25531 polymorphism or its correlates may modulate severity of ADHD and ASD symptoms in children with ASD, but in different ways. These tentative, hypothesis-generating findings require replication with larger independent samples.