The therapeutics of Alzheimer's disease: where we stand and where we are heading.

Few diagnoses in modern medicine evoke more apprehension in patients and their families than Alzheimer disease (AD). Defined as a clinical and pathological entity a century ago, the disorder only came under intense molecular scrutiny in the mid-1980s. Genetic, histopathological, biochemical, and animal modeling studies have combined to provide evidence that the disease may begin with an imbalance between the production and clearance of the self-aggregating amyloid β protein (Aβ) in brain regions serving memory and cognition. This concept has been furthered by recent analyses in humans of cerebrospinal fluid and neuroimaging biomarkers that suggest an approximate sequence of AD-type brain alterations beginning >2 decades before the onset of dementia. Although the Aβ hypothesis of Alzheimer causation does not explain all features of this multifactorial syndrome, experimental agents that lower or neutralize Aβ have become the major focus of therapeutic research. Several clinical trials in mild-to-moderate AD have not met standard cognitive and functional endpoints, but there were important shortcomings in the agent and/or the trial design in each case. Based on the lessons learned, the field has moved on to test potentially disease-modifying agents in mild AD patients or via secondary prevention in presymptomatic subjects bearing amyloid plaques. Immunotherapeutic agents are receiving the most study, but other antiamyloid strategies and, importantly, nonamyloid targets such as tau and neuroinflammation are of great interest. The pace of recent developments augurs well for 1 or more experimental agents being shown to slow cognitive decline without major side effects. However, research funding from all sources will need to increase dramatically and soon to stave off the approaching tsunami of AD.