Often begins in the fifth to seventh decades; in this age group it is nearly as prevalent as AD. Unlike AD, behavioral symptoms may predominate in the early stages of FTD. Three main clinical syndromes. In the behavioral variant, the most common FTD syndrome, social and emotional systems dysfunction manifests as apathy, disinhibition, compulsivity, loss of empathy, and overeating, often but not always accompanied by deficits in executive control. Two forms of primary progressive aphasia, the semantic and nonfluent/agrammatic variants, are also commonly due to FTD. In the semantic variant, pts slowly lose the ability to decode word, object, person-specific, and emotion meaning, whereas pts with the nonfluent/agrammatic variant develop profound inability to produce words, often with prominent motor speech impairment. Any of these three clinical syndromes may be accompanied by motor neuron disease (Chap. 188: ALS and Other Motor Neuron Diseases). FTD may be sporadic or inherited. The most common autosomal dominant mutations involve the C9ORF72, GRN, and MAPT genes. Treatment is symptomatic; no therapies are known to slow progression or improve cognitive symptoms. Many of the behaviors that accompany FTD such as depression, hyperorality, compulsions, and irritability may be helped with SSRIs.