OPTN and amyotrophic lateral sclerosis: Familial ALS accounts for 5 to 10% of all ALS cases, with mutations in several genes including SOD1, TARDBP, OPTN, FUS, UBQLN2 and VCP. Frontotemporal dementia (FTD) is the second most common cause of early onset dementia, and is characterized by progressive degeneration of the frontal and temporal cortex.