ALS is strikingly heterogenous, with 90% of cases being sporadic and the rest due to known alterations in a growing number of genes such as SOD1, TARDBP, FUS and C9ORF72. Hexanucleotide repeat expansion in C9ORF72 (C9ORF72-RE) accounts for approximately 40% of familial ALS and 5% of sporadic disease, making it the most common genetic cause [1]. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.