616 Neurocognitive Disorders
flexibility, abstract reasoning, and response inhibition, are present, but learning and mem-
ory are relatively spared, and perceptual-mot or abilities are almost always preserved in
the early stages. 
Individuals with language-variant major or mild frontotemporal NCD present with pri-
mary progressive aphasia with gradual onse t, with three subtypes commonly described:
semantic variant, agrammatic/n onfluent variant, and logopenic variant, and each variant
has distinctive features and corresponding neuropathology.
“Probable” is distinguished from “possibl e” frontotemporal NCD by the presence of
causative genetic factors (e.g., mutations in the gene coding for microtubule-associated pro-
tein tau) or by the presence of distinctive at rophy or reduced activity in frontotemporal re-
gions on structural or functional imaging. 
Associated Features Supporting Diagnosis
Extrapyramidal features may be prominent in  some cases, with an overlap with syn-
dromes such as progressive supranuclear pa lsy and corticobasal dege neration. Features of
motor neuron disease may be present in some  cases (e.g., muscle atrophy, weakness). A
subset of individuals develop visual hallucinations.
Prevalence
Major or mild frontotemporal NCD is a common  cause of early-onset NCD in individuals
younger than 65 years. Population prevalen ce estimates are in th e range of 2–10 per
100,000. Approximately 20%–25% of cases of  frontotemporal NCD occur in individuals
older than 65 years. Frontotemporal NCD accoun ts for about 5% of all cases of dementia in