In recent years, increasing attention has been directed toward the role of the gut-brain axis in the pathogenesis of neurodevelopmental disorders, particularly Autism Spectrum Disorder (ASD). Among the multiple contributing factors, the integrity of the intestinal barrier appears to play a crucial role. Enhanced paracellular permeability (leaky gut) may allow luminal antigens and microbial metabolites to translocate into the systemic circulation, triggering inflammatory responses that could impact neuropsychological functioning. Several studies suggest that, although intestinal permeability is not universally altered in all individuals with ASD, there exists a subset characterized by selective epithelial dysfunction, especially associated with repetitive and stereotyped behaviors. This project aims to investigate, through a controlled sibling-based design, whether intestinal permeability indices are significantly altered in children with ASD and whether such alterations are specifically correlated with behavioral domains assessed through the ADOS instrument.