There have been no large epidemiological studies on the incidence and prevalence of the<unk>  variants. Though it most likely has been underestimated, onset of<unk>  has been found to occur in the sixth or seventh decade. There are no known environmental risk factors for the progressive<unk> s. However, one observational, retrospective study suggested that vasectomy could be a risk factor for<unk>  in men. These results have yet to be replicated or demonstrated by prospective studies.<unk>  is not considered a hereditary disease. However, relatives of a person with any form of frontotemporal lobar degeneration, including<unk> , are at slightly greater risk of developing<unk>  or another form of the condition. In a quarter of patients diagnosed with<unk> , there is a family history of<unk>  or one of the other disorders in the FTLD spectrum of disorders. It has been found that genetic predisposition varies among the different<unk>  variants, with PNFA being more commonly familial in nature than LPA or SD. The most convincing genetic basis of<unk>  has been found to be a mutation in the GRN gene. Most patients with observed GRN mutations present clinical features of PNFA, but the phenotype can be atypical.
Primary progressive aphasia
Logopenic progressive aphasia
Olive quick decline syndrome
Multiple system atrophy
Dysthanasia
Paroniria
Progressive supranuclear palsy
Semantic dementia