unselected autopsy series. Prevalence estima tes of behavioral variant and semantic lan-
guage variant are higher among males, and prevalence estimates of nonfluent language
variant are higher among females. 
Development and Course
Individuals with major or m ild frontotemporal NCD commonly present in the sixth de-
cade of life, although the age at onset varies from the third to the ninth decades. The dis-
ease is gradually progressive, with median  survival being 6–11 years after symptom onset
and 3–4 years after diagnosis. Survival is shorter and decline is faster in major or mild fron-
totemporal NCD than in typical Alzheimer’s disease. 
Risk and Prognostic Factors
Genetic and physiological. Approximately 40% of individuals with major or mild fron-
totemporal NCD have a family history of early-onset NCD, and approximately 10% show an
autosomal dominant inheritance pattern. A number of genetic factors have been identified,
such as mutations in the gene  encoding the microtubule asso ciated protein tau (MAPT), the
granulin gene (GRN), and the C9ORF72 gene. A number of families with causative muta-
tions have been identified (see the section “D iagnostic Markers” for th is disorder), but many
individuals with known familial transmission do not have a known mutation. The presence
of motor neuron disease is associated  with a more rapi d deterioration. 
Diagnostic Markers
Computed tomography (CT) or structural magnetic resonance imaging (MRI) may show
distinct patterns of atrophy. In behavioral-variant major or mild  frontotemporal NCD,
both frontal lobes (especially the medial frontal lobes) and the anterior temporal lobes are