What Is FTD-ALS? FTD-ALS occurs when symptoms of both frontotemporal dementia and amyotrophic lateral sclerosis develop in the same individual. Each disease affects different parts of the nervous system. FTD primarily damages the frontal and temporal lobes of the brain. These areas are responsible for personality, behavior, decision-making, and language. ALS, on the other hand, attacks the motor neurons that control voluntary muscles, leading to progressive muscle weakness. B