ABSTRACT
A number of studies have suggested that Alzheimer’s disease (AD) does not consist of a single disorder but may comprise several different subtypes. Although a biological basis for heterogeneity of AD is well established, with more than one genetic locus linked to early or late onset of the illness, the various genetic mutations do not appear to be associated with different clinical manifestations. The neuropathological findings of AD in patients with both AD and Parkinsonism often differ from those with AD alone. A number of studies have reported that severe language disability in patients with AD is often associated with early age of onset, rapid progression of the illness, or death. In another report, however, younger persons with AD who manifested severe dysphasia had a higher rate of institutionalization and death than did older persons with AD and a similar degree of language impairment.
