August 31, 2015
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Alzheimer's Disease Causes, Stages, and Symptoms (cont.)

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Who's at risk for getting Alzheimer's disease?

Age

The main risk factor for Alzheimer's disease is increased age. As a population ages, the frequency of Alzheimer's disease continues to increase. Ten percent of people over 65 years of age and 50% of those over 85 years of age have Alzheimer's disease. Unless new treatments are developed to decrease the likelihood of developing Alzheimer's disease, the number of individuals with Alzheimer's disease in the United States is expected to be 13.8 million by the year 2050.

Genetics

There are also genetic risk factors for Alzheimer's disease. Most people develop Alzheimer's disease after age 70. However, less than 5% of people develop the disease in the fourth or fifth decade of life (40s or 50s). At least half of these early onset patients have inherited gene mutations associated with their Alzheimer's disease. Moreover, the children of a patient with early onset Alzheimer's disease who has one of these gene mutations has a 50% risk of developing Alzheimer's disease.

Common forms of certain genes increase the risk of developing Alzheimer's disease, but do not invariably cause Alzheimer's disease. The best-studied "risk" gene is the one that encodes apolipoprotein E (apoE).

  • The apoE gene has three different forms (alleles) -- apoE2, apoE3, and apoE4.
  • The apoE4 form of the gene has been associated with increased risk of Alzheimer's disease in most (but not all) populations studied.
  • The frequency of the apoE4 version of the gene in the general population varies, but is always less than 30% and frequently 8% to 15%.
  • People with one copy of the E4 gene usually have about a two- to three-fold increased risk of developing Alzheimer's disease.
  • Persons with two copies of the E4 gene (usually around 1% of the population) have about a nine-fold increase in risk.
  • Nonetheless, even persons with two copies of the E4 gene don't always get Alzheimer's disease.
  • At least one copy of the E4 gene is found in 40% of patients with sporadic or late-onset Alzheimer's disease.

This means that in majority of patients with Alzheimer's disease, no genetic risk factor has yet been found. Most experts do not recommend that adult children of patients with Alzheimer's disease should have genetic testing for the apoE4 gene since there is no treatment for Alzheimer's disease. When medical treatments that prevent or decrease the risk of developing Alzheimer's disease become available, genetic testing may be recommended for adult children of patients with Alzheimer's disease so that they may be treated.

Estrogen

Many, but not all, studies have found that women have a higher risk for Alzheimer's disease than men. It is certainly true that women live longer than men, but age alone does not seem to explain the increased frequency in women. The apparent increased frequency of Alzheimer's disease in women has led to considerable research about the role of estrogen in Alzheimer's disease. Recent studies suggest that estrogen should not be prescribed to post-menopausal women for the purpose of decreasing the risk of Alzheimer's disease. Nonetheless, the role of estrogen in Alzheimer's disease remains an area of research focus.

Other risk factors for Alzheimer's disease

Other risk factors for Alzheimer's disease include:

  • High blood pressure (hypertension)
  • Heart disease
  • Diabetes
  • Possibly elevated blood cholesterol
  • Individuals who have completed less than eight years of education also have an increased risk for Alzheimer's disease. These factors increase the risk of Alzheimer's disease, but by no means do they mean that Alzheimer's disease is inevitable in persons with these factors.
  • A majority of people with Down syndrome will develop the brain changes of Alzheimer's disease by 40 years of age. This fact was also a clue to the "amyloid hypothesis of Alzheimer's disease"
  • Some studies have found that Alzheimer's disease occurs more often among people who suffered significant traumatic head injuries earlier in life, particularly among those with the apoE4 gene.

In the majority of Alzheimer's disease cases, however, no specific genetic risks have yet been identified.

Medically Reviewed by a Doctor on 8/13/2015

Source: MedicineNet.com
http://www.medicinenet.com/alzheimers_disease_causes_stages_and_symptoms/article.htm

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