Autism Spectrum Disorder (ASD) is characterised by an impairment of social interactions and communication, associated with repetitive behaviour and restrictive interests. Clinical phenotypes of this neurodevelopmental disorder are heterogeneous and surprisingly up to 70% of ASD patients have gastro-intestinal (GI) disorders, associated with ASD severity and influence by feeding disorders. Gut-brain axis seems to play a key role in neurodevelopment and ASD pathophysiology. Indeed an intestinal dysbiosis is observed in ASD, as well as intestinal inflammation and permeability. Aspecific inflammatory pattern suggests neuroinflammation processes in ASD. Neuroinflammation is involved in blood brain barrier (BBB) integrity and there are some arguments for a putative BBBimpairment in ASD. Nevertheless, no study has explored all together these parameters in ASD patients. Here we hypothesise that intestinal dysbiosis in ASD could lead to a BBB impairment through neuroinflammation processes. Furthermore, this association between intestinal dysbiosis and BBB impairment could be influenced by a lot of clinical characteristics, such as ASD severity or GI disorders presence. The principal aim of our study is to determine if the gut microbiota composition is associated with the BBB integrity in ASD. The secondary objectives are i) too identify in children with ASD some physiopathological pathways involved in this association, with a focus on associations betweenintestinal dysbiosis, intestinal permeability, intestinal permeability, the Th1/Th2 immune response, neuroinflammation and the BBB integrity; ii) to evaluate the influence of these associations on several clinical features of ASD such as ASD severity or GI disorders intensity; iii) to evaluate the influence of nutritional status on biological and clinical parameters. This study will assess a lot of clinical and biological parameters together, some of them were never explored in ASD children. It will allow to better understand ASD pathophysiology, to highlight new therapeutic pathway, and to promote personalised medicine.