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

BackgroundThe 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.MethodsMothers and teachers completed a validated DSM-IV-referenced rating scale for ADHD and ASD symptoms in 118 children with ASD.ResultsAnalyses indicated that children with at least one copy of the S or LG 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 LA allele. Conversely, mothers' ratings indicated that children with LA/LA genotype had more severe ASD social deficits than S or LG 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.ConclusionThe 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.

► 5-HTTLPR/rs25531 is associated with both ADHD and autism spectrum disorder.
► S + or LG+ genotypes had more severe hyperactivity than the LA/LA group.
► The LA/LA genotype had more severe ASD social deficits than the S/S group.
► Results suggest a potential model for co-morbidity within the ASD clinical phenotype.