Alzheimer’s & Dementia Causes, Risk Factors | Research …

Posted: December 29, 2014 at 11:46 am

What We Know Today About Alzheimer's Disease

The Search for Alzheimers Causes and Risk Factors

While scientists know Alzheimer's disease involves progressive brain cell failure, the reason cells fail isn't clear. Like other chronic conditions, experts believe that Alzheimer's develops as a complex result of multiple factors rather than any one overriding cause. Both age and genetics have been identified as risk factors, but many questions still remain. The discovery of additional risk factors will deepen our understanding of why Alzheimer's develops in some people and not others.

Although Alzheimer's is not a normal part of growing older, the greatest risk factor for the disease is increasing age. After age 65, the risk of Alzheimer's doubles every five years. After age 85, the risk reaches nearly 50 percent.

Another Alzheimer's risk factor is family history. Research has shown that those who have a parent, brother, sister or child with Alzheimer's are more likely to develop the disease. The risk increases if more than one family member has the illness. When diseases tend to run in families, either heredity (genetics) or environmental factors or both may play a role.

There are two categories of genes that influence whether a person develops a disease: (1) risk genes and (2) deterministic genes. Researchers have identified Alzheimer's genes in both categories.

Everyone inherits a copy of some form of APOE from each parent. Those who inherit one copy of APOE-e4 have an increased risk of developing Alzheimer's. Those who inherit two copies have an even higher risk, but not a certainty. In addition to raising risk, APOE-e4 may tend to make symptoms appear at a younger age than usual. Scientists estimate that APOE-e4 is implicated in about 20 percent to 25 percent of Alzheimer's cases.

In 2003, the Alzheimer's Association partnered with the National Institute on Aging to begin recruiting participants for the National Alzheimer's Disease Genetics Study, a federal initiative to collect and bank blood samples from families with several members who developed Alzheimer's disease late in life. The goal is to identify additional Alzheimer's risk genes. The study continues to seek participants.

Although the genes that cause "familial Alzheimer's" are rare, their discovery has provided important clues that help our understanding of Alzheimer's. All of these genes affect processing or production of beta-amyloid, the protein fragment that is the main component of plaques. Beta-amyloid is a prime suspect in decline and death of brain cells. Several drugs now in development target beta-amyloid as a potential strategy to stop Alzheimer's disease or significantly slow its progression.

Two international investigations are under way to gain further insight into Alzheimer's disease by studying individuals with deterministic Alzheimer's genes: (1) The Dominantly Inherited Alzheimer Network (DIAN), funded by the National Institute on Aging (NIA), includes 10 flagship research centers in the United States, the United Kingdom and Australia. (2) The Alzheimer's Prevention Initiative (API) focuses on an extended family in Antioquia, Colombia, in South America. At 5,000 members, this is the world's largest family in which a gene that causes Alzheimer's has been identified. API collaborators include DIAN. Learn more on our Treatment Horizon page.

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