Alzheimer's disease and Down's syndrome: treating two paths to dementia.

Successful therapy of dementia, like any disease, depends upon understanding its pathogenesis. This review contrasts the dominant pathways to dementia which differ in Alzheimer's disease (AD) and in Down's syndrome (DS). Impaired clearance of neurotoxic amyloid beta peptides (Abeta) leads to dementia in AD. In DS over-production of Abeta plays the dominant role in the development of dementia. It follows, therefore, that the therapy of AD and DS should reflect a different balance between the dominant agent that inhibits the synthesis of Abeta in the brain in AD and increase the clearance of Abeta from the cerebrospinal DS.