HTT and juvenile Huntington disease: Given that the host genetics greatly influences the physical structure of the gut, which then determines the chemical and physical environment inhabited by the gut microbiome,47 one possible explanation is that the expression of mutant HTT (via the human Huntington’s disease transgene) by the Huntington’s disease mice altered the gut mucosal lining and overall architecture, thus exerting stochastic effects on microbiome composition while impeding the colonization of microbes adapted to a healthy gut.