Clinical features of a neuropathologically verified familial Alzheimer's cohort with onset in the fourth decade: comparison with senile onset Alzheimer's disease and etiopathogenic implications.

Clinical and pathologic features of a family with early onset, autosomal dominant, familial Alzheimer's disease (AD) are compared and contrasted with senile onset dementia of the Alzheimer type. Late onset AD has previously been observed to have a characteristic progression and clinical course. A previously unreported pedigree, with two siblings and their father affected, of early clinical onset is presented. Molecular genetic study of this family using in situ chromosome hybridization showed an apparent marker on chromosome 9. This early onset form of AD is observed to be clinically consistent with the common late onset form of AD, but follows a more rapid course. An etiopathogenic model explaining the early onset, and other forms of AD is presented.