Research is exploring the relationship between hexanucleotide repeat expansions in the C9orf72 gene and amyotrophic lateral sclerosis, including the potential for these expansions to serve as diagnostic tools and risk factors. The expansions have been linked to impaired microglial response and the formation of RNA condensates, and are also associated with frontotemporal dementia. Studies, including those using mouse models, are investigating the role of C9orf72 expansions in these diseases and potential therapeutic strategies.