The role of gut microbiota in Autism spectrum disorder

Human microbiota are colonies of microorganisms located in different parts of the human body with diverse functions. Healthy gut microbiota comprises differing ratios of microoganisms wholly contributing to metabolic and other molecular reactions in a healthy, functioning body. After the demonstration of the bidirectional interaction between the central nervous system and gut microbiota through neuroendocrine, neuroimmune, and autonomic nervous mechanisms, investigations have been started on the microbiota-gut-brain axis in psychiatric disorders. Autism spectrum disorder (ASD), which is a neurodevelopmental disorder of early childhood, is one of these disorders. Most of such studies were cross-sectional and mainly investigated the bacterial species. Changes in gut microbiota composition and the leaky gut syndrome are some of the hypotheses proposed to explain the core symptoms and gastrointestinal (GI) symptoms of ASD. Probiotics, prebiotics, fecal microbiota transplantation, diet have been proposed as treatment options. However, the role of microbiota in diagnosis, follow-up, and treatment is not yet clear. The bidirectional interaction between central nervous system and intestinal microbiota makes it difficult to establish the cause-effect relationship. The current data on microbiota may be useful to plan patient-specific treatment in autistic children with GI symptoms. This article aims to review the results of the studies on microbiota in animal models and children and discuss the emerging clinical relationship of ASD and gut microbiota.