Etiology

It is believed that there is a strong familial component in about 40 percent of cases of FTD, and the pattern of inheritance appears to be autosomal dominant in 80 percent of familial FTD cases (Stevens et al., 1998).

A number of kindreds with autosomal dominant FTD have been shown to have abnormalities of the chromosome 17 gene coding for tau (Foster et al., 1997). These families show clinical heterogeneity: In addition to the characteristic findings of FTD, psychosis, amyotrophy (muscular wasting), and parkinsonism are variably present in patients with these tau gene mutations. This heterogeneity is thought to arise from the fact that different gene mutations affect tau processing and functioning differently.

Other lines of evidence suggest that tau mutations may be sufficient but not necessary for the appearance of an FTD syndrome. Some of the chromosome 17 kindreds do not seem to have a tau mutation, and one Danish kindred with an autosomal dominant FTD has been found to have an abnormality on chromosome 3 (Brown et al, 1995). FTD associated with motor neuron disease has been linked to chromosome 9 (Hosler et al., 2000).

The apolipoprotein E genotype does not appear to influence the risk for FTD. No social, occupational, geographical, or environmental factors have been found to correlate with FTD.

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