Any amyotrophic lateral sclerosis in which the cause of the disease is a mutation in the PFN1 gene. The disease is amyotrophic lateral sclerosis type 18 (MONDO_0013891, a Monarch Disease Ontology id). Also known as: ALS18, PFN1 amyotrophic lateral sclerosis, amyotrophic lateral sclerosis 18, amyotrophic lateral sclerosis caused by mutation in PFN1.