The large majority of ALS cases occur sporadically, but 5–10% of ALS patients have a family history, usually with autosomal dominant inheritance, and approximately two thirds of them harbor mutations in one (or sometimes more) of > 20 genes, the most common being the (G4C2)n hexanucleotide repeat expansion (HRE) in the C9orf72 gene and mutations in the genes SOD1, TARDBP, and FUS (Mejzini et al., 2019). The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.