Abstract
BACKGROUND: Recent studies have indicated that there are imbalances in neurotransmitter levels in children with autism spectrum disorder (ASD). Alterations in peripheral blood and urinary neurotransmitter levels may serve as biomarkers for ASD. METHODS: This study aims to explore the relationship between neurotransmitter levels and the severity of ASD. Totally, forty sex-, age-, and ethnically matched typically developing (TD) children were recruited to compare the neurotransmitter levels with ASD aged over 3 years. Differences in plasma and urinary neurotransmitter levels between TD children and children with ASD were compared using the Mann-Whitney U test. For the indicators that showed significant differences, further multivariate regression analysis was conducted to assess the association between individual neurotransmitters and Autism Diagnostic Observation Schedule, Second Edition (ADOS-2) Calibrated Severity Score (CSS). Finally, a restricted cubic spline (RCS) model was applied to explore the dose-response relationship between neurotransmitter concentrations and ADOS-2 CSS. RESULTS: Plasma levels of dopamine (DA), normetanephrine (NMN), 5-hydroxytryptamine (5-HT), γ-aminobutyric acid (γ-GABA) levels in ASD were significantly higher than those in TD children while plasma levels of norepinephrine (NE), tyrosine (Tyr) were significantly lower. Urinary levels of NMN were significantly lower, while epinephrine (E), NE, vanillylmandelic acid (VMA), homovanillic acid (HVA) were significantly higher in children with ASD compared to TD. After adjusting for confounders of age, sex and BMI, plasma GABA was negatively associated with ADOS-2 CSS, while urinary NE and NMN were positively associated with ADOS severity scores (P ＜ 0.05). Multiple regression analysis indicated that plasma GABA and urinary NE and NMN levels explained 26.9%, 24.8% and 15.8% of the variability in ADOS-2 CSS for ASD. The RCS analysis results were largely consistent with the linear regression analysis results. Plasma GABA and urinary NE, and NMN exhibited a linear correlation with ADOS-2 CSS. Plasma NE and Tyr showed a U-shaped curve relationship with the ADOS-2 CSS (P< 0.05). CONCLUSIONS: A significant negative correlation was observed between plasma GABA neurotransmitter concentrations and ASD severity. In contrast, NE and NMN levels in urine showed significantly positive correlations with ASD severity. Both excessively low and excessively high plasma NE and Tyr levels may be associated with more severe autism symptoms, suggesting a disruption in peripheral neurotransmitter levels in children with ASD. Future studies with larger sample sizes are required for prediction and validation. The peripheral neurotransmitters may serve as potential auxiliary biomarkers for assessing the severity of autism.