Given that cognitive impairment and particularly frontotemporal dementia (FTD) can be found in up to 10%–15% of patients with ALS [123], it is interesting that in this particular form of dementia, blood and CSF NF-L levels are associated with functional outcome, brain atrophy, and severity, and can be used to discern FTD from other types of dementia and healthy controls but not be used to distinguish between FTD subtypes [124,125,126]. This evidence concerns the gene NEFL and Brain atrophy.