Inheritance of frontotemporal dementia.

BACKGROUND: Previous studies of families with fronto-temporal dementia (FTD) support an autosomal dominant inheritance pattern, but most studies have described genetic transmission in individual families specifically selected for the presence of multiple affected individuals.
OBJECTIVE: To investigate the familial presentation and inheritance of FTD and related disorders among a large group of FTD index cases unselected for family history of dementia. DESIGN AND
SETTING: We interviewed family members and reviewed medical records and autopsy reports at a university hospital and a university-affiliated hospital to determine the frequency of familial FTD and the most likely mode of inheritance. Characteristic families with the disorder are described, along with the history, clinical findings, and neuroimaging results in affected members of these families. PATIENTS AND PARTICIPANTS: The 42 index cases of FTD had a mean age of onset of 56.1 years (range, 40-69 years). Of these patients, 21 (50%) were women. All but one of the patients were white. Participants included male and female spouses and children of the index cases. family member with an FTD spectrum disorder and were considered familial cases. The majority (17 [89%]) of familial FTD cases showed a pattern consistent with dominant inheritance. If depression is excluded, familial cases decrease from 19 (45%) to 17 (40%), of which 15 (88%) showed a dominant transmission pattern. The initial presentations in the nonindex familial cases varied but most frequently consisted of personality and behavioral changes that preceded cognitive impairment (19 [43%]), followed by psychiatric illness (14 [33%]), dementia without behavioral change (5 [11%]), amyotrophic lateral sclerosis (5 [11%]), and parkinsonism (2[5%]). Two of the affected nonindex cases had dual presenting diagnoses. The average age of onset was 56.1 years and did not differ significantly between familial and nonfamilial cases. Onset of FTD-related symptoms occurred after the age of 65 years in only 4(10%) of 42 index cases and 3 (5%) of 60 affected relatives.
CONCLUSIONS: Familial FTD is usually inherited in an autosomal dominant pattern. The initial onset is insidious, often consisting of mood and behavioral changes occurring in presenile years that are often erroneously attributed to other nonneurologic causes. Although the precise incidence of FTD in North America is not known, it is one of the most common presenile dementias.