Alzheimer's disease is a devastating, progressive brain disease that erodes memory and other cognitive skills. Eventually, persons with Alzheimer's lose the ability to recognize family, speak or do simple tasks. According to the National Institute on Aging, the disease is age-related in two ways. First, approximately 90 percent of Alzheimer's cases arise after age 65 with prevalence increasing with age. After 85, half of the population shows signs of Alzheimer's. Second, a small percent have early-onset of the disease with symptoms appearing before age 55, sometimes evident by the 30s or 40s.
Background
Alzheimer's accounts for half of all dementia cases. It is characterized by a gradual and irreversible loss of cognitive functioning and interference with daily life. There are no clinical tests to diagnose it, so diagnosis is accomplished with a combination of neuro-psychological assessments and eliminating other causes of dementia. Alzheimer's is the seventh leading cause of death in the U.S.
According to the Alzheimer's Organization, up to 5.1 million people in the U.S. may have Alzheimer's.
Late-Onset AD
Alzheimer's is not a part of normal aging, but the risk of the disorder increases with age. According to the Alzheimer's Organization, age is Alzheimer's biggest risk factor. Five percent of people between age 65 and 74 have the disease. By age 85, half of this population demonstrates some level of Alzheimer's characteristics.
The most common clinical pattern, accounting for about 90 percent of cases, is "late-onset" Alzheimer's, developing after age 65. Late-onset Alzheimer's has a genetic component, with about 40 percent of persons affected having a mutation in the APOE gene. However, the genetic contribution is unclear. Sixty percent of those with late-onset of the disease do not carry this genetic mutation and not everyone with the mutation goes on to develop it.
Early-Onset AD
Five to 10 percent of persons with Alzheimer's have an early-onset for the disease. Although some with early-onset Alzheimer's develop symptoms in their 30s and 40s, it is more common to see early-onset symptoms appear in people in their 50s.
Early-onset Alzheimer's tends to run in families. Many have inherited one of three genes closely associated with early-onset of the disease. According to the Mayo Clinic, although not all early onset Alzheimer's can be traced to family histories, if an individual tests positive for one of these genetic mutations, he is very likely to develop early-onset Alzheimer's.
Normal Aging and Memory
Some signs of forgetfulness and short-term memory loss are common to both normal aging and Alzheimer's. Key differences between normal age-related memory difficulties and this disease are the speed of the progressive memory loss and the eventual inability to follow instructions, use notes as reminders or to take care of themselves.
Aging Population
According to the National Institute on Aging, unless Alzheimer's can be effectively treated or prevented, the numbers of persons with it may swamp the U.S. health care system. The U.S. population over 65 is expected to grow from 39 million in 2008 to 72 million in 2030. The fastest growing segment is that over age 85.
References
- National Institutes of Health: National Institute on Aging: Alzheimer's Disease Fact Sheet.
- Mayoclinic.com: Early Onset Alzheimer's: When Symptoms Begin Before 65.
- Alzheimer's Association: Risk Factors.
- Fisher Center for Alzheimer's Research Foundation: Difference Between Alzheimer's and Normal Age-Related Memory Changes, 2010.
