More than 35 million people worldwide — 5.5 million in the United States — have Alzheimer's disease, a deterioration of memory and other cognitive domains that leads to death within 3 to 9 years after diagnosis. Alzheimer's disease is the most common form of dementia, accounting for 50 to 56% of cases at autopsy and in clinical series. Alzheimer's disease combined with intracerebral vascular disease accounts for another 13 to 17% of cases.
The principal risk factor for Alzheimer's disease is age. The incidence of the disease doubles every 5 years after 65 years of age, with the diagnosis of 1275 new cases per year per 100,000 persons older than 65 years of age. 1 Data on centenarians show that Alzheimer's disease is not necessarily the outcome of aging2; nevertheless, the odds of receiving the diagnosis of Alzheimer's disease after 85 years of age exceed one in three. As the aging population increases, the prevalence will approach 13.2 to 16.0 million cases in the United States by mid-century.3
Many molecular lesions have been detected in Alzheimer's disease, but the overarching theme to emerge from the data is that an accumulation of misfolded proteins in the aging brain results in oxidative and inflammatory damage, which in turn leads to energy failure and synaptic dysfunction.