Alzheimer's Disease Early Signs

Age-Specific Incidence of Alzheimer's Disease

 

Overview

Alzheimer's disease is the most common cause of progressive dementia in elderly people, according to Online Mendelian Inheritance in Man, or OMIM. In Alzheimer's disease, nerve cells in the brain die, killed by the accumulation of abnormal protein masses called senile plaques and neurofibrillary tangles. The loss of brain cells impairs memory, inhibits learning and critical thinking, changes behavior and ultimately robs patients of physical functions, as well.

Statistics

According to the Mayo Clinic, the incidence of Alzheimer's disease increases with age. Between the ages of 65 to 74, about 5 percent of people have Alzheimer's disease, but over the age of 85, about 50 percent of people have Alzheimer's. Over 90 percent of all cases of Alzheimer's disease occur in people aged 65 or older, says the National Institute of Neurological Disorders and Stroke. The Merck Manual states that on average, victims of Alzheimer's disease die about 7 years after their diagnosis.

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Physiology

Alzheimer's disease is progressive, with patients showing a gradual decline in memory and critical thinking skills. The symptoms first appear when the characteristic plaques and tangle in brain cells accumulate to the level that decreased function becomes obvious to other people. Over time, as more damage accumulates, symptoms worsen and progress. Because it takes time for the damage to accumulate, Alzheimer's typically appears in older people.

Early Onset

Some families suffer from a repeating occurrence of Alzheimer's disease among relatives as young as their 30s or 40s. This form of Alzheimer's disease, referred to as the "early-onset" type, results from an inherited mutation in one of three particular genes. Mutations in the gene called APP, encoding amyloid precursor protein, can cause early onset Alzheimer's. In one study cited by OMIM, family members with a mutation in APP developed Alzheimer's disease at an average age of 43.

Late Onset

When Alzheimer's symptoms first appear in people 65 or older, the disease is classified as "late onset." Late-onset Alzheimer's disease results from the combined effects of environmental and genetic factors. The Merck Manual explains that people who a have certain form of the gene encoding apolipoprotein E, called apoE4, have a higher risk of developing Alzheimer's disease, and show symptoms at a younger age, while people with the apoE2 allele are less likely to develop Alzheimer's disease at any age.

Normal Aging

Although the incidence of Alzheimer's disease increases with age, it is not a part of normal aging. Elderly people often suffer lapses of memory, but Alzheimer's disease affects not only memory but also the ability to learn, make judgments and analyze information. The Merck Manual stresses that the impairment of memory due to aging is not necessarily a sign of or precursor to Alzheimer's disease.