Using this novel antibody we developed a highly specific and sensitive sandwich ELISA to determine the dynamic nature of this cryptic exon-encoded neoepitope in CSF from individuals with sporadic ALS, as well as in CSF and blood from presymptomatic and symptomatic individuals with C9orf72 mutations causing familial ALS–FTD17,18. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.