Most studies on the relationship between microbiome and psychiatric symptoms have been conducted in autism spectrum disorders (ASD), where gastrointestinal symptoms, increased intestinal permeability and microbiome alterations (such as elevated levels of Clostridium bacteria) have been frequently reported in individuals with ASD [15,16], along with increased levels of lipopolysaccharides and pro-inflammatory cytokines (such as interleukin-6 (IL-6)) [13]. This evidence concerns the gene IL6 and autism spectrum disorder.