The Long and Short of It: Serotonin Transporter Allele Variants and Emotion Processing in Adults with Autism Spectrum Disorders

Background: The serotonin transporter linked polymorphic region (5-HTTLPR) has 2 common variants: the short allele (S) and long allele (L). Previous work has demonstrated differences in neural and behavioral responses of individuals with at least one S allele to faces with negative emotions including greater activation of the fusiform gryus for fearful faces and faster responses to angry faces. Prior work has also reported reduced amplitudes in electrophysiological responses to angry faces in comparison to happy and neutral faces among carriers of the S allele.

Objectives: To test the relation between the pattern of electrophysiological neural response to emotional faces in individuals with ASD and neurotypical development based on the 5-HTTLPR allele profile. 

Methods: Subjects were 24 adults with ASD, 16 of whom had at least one S allele; and 21 adults with typical development, 17 of whom had at least one S allele. All participants were Caucasian and had Full Scale IQs in the average or above average range. ASD diagnosis was confirmed with the ADOS, ADI-R and DSM-IV-TR. Electrophysiological responses were continuously recorded with high-density EEG as participants viewed static images of faces with fearful, happy, or neutral expressions. The P100, N170, N250 and N400 components were examined in electrodes over the lateral posterior region in the right and left hemisphere.

Results: Similar to previous reports with typically developing individuals, among participants with ASD, there was a significant interaction between allele length (S vs. L) and facial expression for the amplitude of the P100, F(2,44) = 4.3, p = .03. This interaction was not observed for later components. Given that individuals with the S allele may be more sensitive to stimuli conveying negative emotions, the S carriers in the ASD and TD group were also compared. There were no differences in the pattern of neural responses of S allele carriers with ASD (n=16) versus those with typical development (n=17) across the 4 components examined, though there were main effects of facial emotion. Finally, with S and L carriers combined, comparison of the ASD versus TD groups revealed no diagnostic group by emotion interactions or main effects of group for the 4 components.

Conclusions: These initial findings suggest that serotonin transporter linked polymorphic region (5-HTTLPR) allele length may be a useful way to better understand the individual performance of individuals on the autism spectrum, particularly in early visual attention to emotional information. The use of genetic information may provide meaningful ways to parse the heterogeneity of symptoms.