<p>Autism spectrum disorder (ASD) is a complex neurodevelopmental condition with a multifactorial etiology involving both genetic and environmental factors. Although previous studies have identified altered levels of circulating proteins in individuals with ASD, the functional significance of these peripheral biomarkers remains largely unclear. In this study, we recruited a well-characterized cohort of young Arab children with ASD (n = 100) and matched controls (n = 60), aged 2–4 years, in Qatar. We used a multimodal approach, integrating data from proteomics, transcriptomics, induced pluripotent stem cell (iPSC)-derived cortical neurons, cellular imaging, functional assays using microelectrode recordings, and behavioral assays in <i>Drosophila</i> models. High-throughput screening of plasma samples revealed considerable heterogeneity in circulating proteomic profiles across different Arab subpopulations; therefore, we focused our subsequent analyses on Qatari children. We identified elevated levels of several neuronal proteins in the peripheral circulation of individuals with severe, but not mild, ASD symptoms. Furthermore, we found that neurons derived from the severe ASD group showed increased MAP2⁺/DCX⁺ cell counts, upregulated expression of genes associated with neuronal activity, and increased neuronal hyperexcitability in functional assays. Moreover, targeted overexpression of these proteins specifically in the blood of <i>Drosophila</i> models was sufficient to induce ASD-relevant behaviors. Together, our findings reveal key links between peripheral protein dysregulation and neuronal function and behavior, offering new insights into systemic contributions to ASD pathophysiology and highlighting potential therapeutic targets for mitigating symptom severity.</p>