C9orf72 and amyotrophic lateral sclerosis: Poly-glycine-proline in CSF, measured by ELISA, has attracted attention as a potential biomarker in C9orf72 gene expansion carriers in both behavioural-variant FTD and ALS.49-51 Asymptomatic mutation carriers have also been found to have elevated CSF poly-glycine-proline, and levels are raised in those diagnosed with ALS, in most, but not all mutation carriers.50 The size of the dipeptide repeat proteins is, however, unknown,49 nor if present in urine.