While ALS-FTD is not regarded as a developmental disease, mutations in some ALS-causing genes have been associated with juvenile-onset ALS with learning difficulties and autism,84,85 and studies have suggested that network degeneration in asymptomatic carriers of C9orf72 mutations could be a consequence of aberrant patterning during development.38 This evidence concerns the gene C9orf72 and frontotemporal dementia.