Any frontotemporal dementia with motor neuron disease in which the cause of the disease is a mutation in the C9orf72 gene. The disease is frontotemporal dementia and/or amyotrophic lateral sclerosis 1 (MONDO_0007105, a Monarch Disease Ontology entry). Also known as: ALSFTD, C9ORF72 frontotemporal dementia with motor neuron disease, C9orf72 frontotemporal dementia with motor neuron disease, FTDMND, amyotrophic lateral sclerosis and/or frontotemporal dementia, frontotemporal dementia and/or amyotrophic lateral sclerosis type 1, frontotemporal dementia and/or motor neuron disease, frontotemporal dementia with motor neuron disease caused by mutation in C9ORF72.