Repetitive and restrictive behaviours, unlike sensory symptoms, may not be associated with brain serotonin transporter availability

Background Currently, we lack a clear understanding of the biological mechanisms underlying the different symptom domains of autism, and no approved pharmacological treatments are available. Autism is defined by social communication (SC) difficulties and non-social symptoms, including inflexible, repetitive and restrictive behaviours (RRB) and sensory reactivity. These symptom domains might disperse different biological constructs. Understanding the distinct biological underpinnings of autism symptoms is essential for advancing targeted, precision-based treatments. In our previous work we found correlations between social cognition and serotonin transporter (5-HTT) availability, and here we study other symptom domains in relation to 5-HTT availability in the brain. Results Fifteen participants diagnosed with autism and fourteen matched control subjects underwent positron emission tomography (PET) with the radioligand [ ¹¹ C]MADAM which binds to 5-HTT. 5-HTT availability did not correlate to any of our RRB-related measures of behavioural flexibility (cognitive tests (Delis-Kaplan Executive Function System verbal fluency and the Tower) and self-rating scales (Social Social Responsiveness Scale and Autism Spectrum Quotient subscales), and our behavioural flexibility index based on three personality tests). However, in a smaller subsample, we found negative correlations between sensory reactivity (as measured by Sensory Reactivity Test in the Autism Spectrum scale) and 5-HTT binding in most cortical brain regions. Conclusions 5-HTT may be less important for RRBs than for SC and sensory symptoms. Further studies investigating the biology of distinct autism symptoms are warranted to aid the development of precision medicine.