Interestingly, the environment, especially variation in gut microorganisms, seems to directly influence the pathological phenotype of C9orf72−/− mice [37] and HSV-2 latent infection in the spinal cord of mice results in altered microglia and leucocyte infiltration accompanied by a decrease in C9orf72 protein levels [38]. The gene discussed is C9orf72; the disease is disease arising from reactivation of latent virus.