Circulating Levels of 5-HT and BDNF in Adults with Autism Spectrum Conditions: An Investigation in a Sample of Subjects with Autism Spectrum Disorder, their First-degree Relatives and Controls

Background: Several studies investigated circulating levels of serotonin (5-HT) and brain-derived neurotrophic factor (BDNF) in children with Autism spectrum disorder (ASD). More limited literature focused on ASD adults or on populations with sub-threshold autism spectrum manifestations, such as relatives of ASD probands. This study aimed to investigate 5-HT and BDNF levels in adults with autism spectrum conditions. Correlations between levels of biochemical variables and ASD symptoms were also eval-uated. Methods: a sample of ASD adults, their first-degree relatives (Broad autism phenotype, BAP group), and controls were recruited and assessed with psychometric scales. Blood samples were collected from all participants. 5-HT and BDNF levels were measured by means of ELISA kits. Results: ASD adults showed significantly lower platelet-poor plasma (PPP) 5-HT levels than BAP and control groups. No significant difference was found among groups for PPP BDNF levels and intra-platelet 5-HT levels. 5-HT levels were reported to be specifically correlated with some autism symptoms. Conclusion: This work highlighted the presence in ASD adults of reduced PPP 5-HT levels than in other groups, without significant differences with respect to BDNF levels, sup-porting the hypothesis that biochemical correlates of ASD in adults may be different from those typically reported in children.