Alzheimer’s disease, a progressive, degenerative brain disorder, is the sixth leading cause of death in the United States. While Alzheimer’s disease itself does not cause death, progressive loss of memory and loss of basic motor skills can eventually be fatal in Alzheimer’s patients.
In a small percentage of cases, what is known as familial Alzheimer’s disease is linked to patient’s family history. However, genes do not have any known role in late-onset Alzheimer’s, the most common form of the disease.
Dementia and Alzheimer’s Disease
Dementia, caused by injury or changes inside the brain, is a term used to describe memory loss and a decrease of mental abilities. The most common cause of dementia is Alzheimer’s disease. Between 50 and 70 percent of dementia cases are related to Alzheimer’s disease, according to the Alzheimer’s Association.
Other causes of dementia include severe head trauma, HIV/AIDS, Huntington’s Disease, and Parkinson’s Disease.
Genetics Linked to Alzheimer’s Disease
Almost all cases of Familial Alzheimer’s disease occur early in life. Early-onset Alzheimer’s disease only accounts for between 5 and 10 percent of all Alzheimer’s disease cases.
Because the vast majority of Alzheimer’s disease cases are sporadic (meaning they occur without a family history or genetic predisposition), simply having a relative with Alzheimer’s disease does not necessarily increase your risk for developing the illness. Your risk for developing Familial Alzheimer’s disease increases if more than one relative or family member has the disease.
Familial Alzheimer’s Disease
Geneticists who study Alzheimer’s genetics separate cases of Alzheimer’s disease between those cases that run in families, known as Familial Alzheimer’s disease, and sporadic Alzheimer’s disease that have no known genetic component. Sporadic cases are much more common than familial cases, and usually occur in the later stages of life.
Early-Onset Alzheimer’s Disease
Early-onset Alzheimer’s disease is the term used to describe cases of Alzheimer’s diagnosed before a person turns 65. Early-onset cases are rare, and in some cases, linked to a family history.
Approximately half of early-onset Alzheimer’s disease cases are related to family history. In most cases, in order to develop Familial Alzheimer’s disease, a person diagnosed with Alzheimer’s disease must have two first-degree relatives with a history of Alzheimer’s disease.
Genetic researchers of Familial Alzheimer’s disease are interested three specific gene variations (called alleles) of a gene known as apolipoprotein E (APOE). The APOE gene is responsible for coding protein in lipoproteins (complexes of fat plus protein).
Tests revealing APOE variations only indicate a potential risk for developing Alzheimer’s and cannot in any way predict the future. A person who has inherited the specific gene variations may never develop Alzheimer’s disease, and a person who has not inherited those particular alleles may still develop Alzheimer’s disease.
Late-onset Alzheimer’s Disease
Most cases of late-onset Alzheimer’s disease are not linked to a genetic predisposition or family history, but to increased age, the single greatest risk factor for developing Alzheimer’s disease. Between the ages of 65 and 85, your risk of developing Alzheimer’s disease doubles every 5 years.
Genetic Testing for Alzheimer’s Disease
There are genetic tests to screen for the known genes that contribute to Alzheimer’s disease. These tests may detect a genetic disposition, which may or may not result in a person actually developing Alzheimer’s disease.
Similarly, a person may develop sporadic Alzheimer’s disease even if they do not have genes linked to the disease. As Alzheimer’s disease research develops, more genetic links to Alzheimer’s disease may be uncovered. Armed with this information, researcher may be able to develop new treatments and screening tests for the disease.
Alzheimer’s Association. (2008). Alzheimer’s facts and figures. Retrieved November 11, 2008, from the Alzheimer’s Association Web site at: http://www.alz.org/alzheimers_disease_facts_figures.asp.
Alzheimer’s Association. (2008). Dementia. Retrieved November 11, 2008, from the Alzheimer’s Association Web site at: http://www.alz.org/alzheimers_disease_dementia.asp.
The Fisher Center for Alzheimer’s Research Foundation. (2008). Genetic (inherited) factors. Retrieved November 11, 2008, from the Fisher Center for Alzheimer’s Research Foundation Web site at: http://www.alzinfo.org/alzheimers-genetic.asp.