C9orf72 and frontotemporal dementia: Conversely, supplementation of A. muciniphila was associated with increased motor neurons in the spinal cord, improved motor function, reduced brain atrophy, and prolonged lifespan.223 The gut microbiome is also closely linked to C9orf72 function.57 The hexanucleotide (GGGGCC) repeat expansion in the C9orf72 gene has been identified as the leading genetic cause of ALS and FTD.226–228 It was found that the gut microbiota is a potent modifier of disease severity and microglial activation in C9orf72-mutant mice raised in different environments.