Alzheimer Disease (AD)

Background: Alzheimer disease (AD) is the most common cause of dementia, which is an acquired cognitive and behavioral impairment of sufficient severity to markedly interfere with social and occupational functioning.

Frequency:

* In the US: The lifetime risk of AD is estimated to be 1:4-1:2. More than 14% of individuals older than 65 years have AD, and the prevalence increases to at least 40% in individuals older than 80 years.

* Internationally: Prevalences similar to those in the United States have been reported in industrialized nations. Countries experiencing rapid increases in the elderly segments of their population have rates approaching those in the United States.

Mortality/Morbidity:

* Second to only certain cancers and cardiovascular disease, AD is frequently considered a leading cause of death in the United States.

* The primary cause of death is intercurrent illness, such as pneumonia, in a patient who has experienced the debilitating effects of AD for many years.

Race: Some claim that AD affects certain ethnic and racial groups more severely than others, but more study is needed before reliable statements about racial predilections can be made.

Sex: AD affects both men and women. Many studies indicate that the risk of AD is significantly higher in women than in men. Some authorities have postulated that this difference is due to the loss of the neurotrophic effect of estrogen in postmenopausal women. Other factors may also influence this relative difference.

Age: The prevalence of AD increases with age.

* AD is most prevalent in individuals older than 60 years. Some forms of familial early-onset AD can appear as early as the third decade, but this represents a subgroup of the less than 10% of all familial cases of AD.

* More than 90% of cases of AD are sporadic and occur in individuals older than 60 years.

* Of interest, results of some studies of nonagenarians and centenarians suggest that the risk decreases in individuals older than 80 or 90 years. If so, age is not an unqualified risk factor for the disease, but further study of this matter is needed.