Rare Gene Mutation Affecting Immunity Linked to Alzheimer's

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Scientists working on two unrelated studies have reported a link between Alzheimer's disease and a rare gene that affects a person's immune system. They add credibility to recent thinking about the role of the immune system in the development of this form of dementia.

According to Medical News Today, research teams from University College London (UCL) and the Iceland-based company deCode Genetics concluded that a rare mutation in the gene known as TREM2 increases the risk of getting Alzheimer's. This gene helps signal the immune system to mount responses to inflammation.

The Alzheimer's Association says this disease is the sixth-leading cause of death in the United States. Of the top 10 causes, it's the only one that can't be prevented, cured, or slowed. One in every eight U.S. seniors lives with the disorder.

There are two forms of the disease. Early-onset Alzheimer's affects people younger than 60. The late-onset form is far more common, according to PubMed Health.

Scientists from 44 institutions participated in the UCL-led study, which followed 25,000 individuals. They found a set of rare mutations that appeared more frequently in 1,092 Alzheimer's patients than in the 1,107 healthy control-group subjects. The most common mutation was one called R47H, which the researchers learned significantly increases the chance of developing the illness.

The study led by deCode also noted a strong link between the R47H mutation and the disease. The researchers also discovered that older individuals who had the mutation but not Alzheimer's had poorer cognitive function than normal. They identified nearly 41 million markers in individuals from the United States, Germany, Norway, and the Netherlands.

Earlier studies suggested that TREM2 is important in clearing cell debris and amyloid protein, a substance linked to Alzheimer's brain plaques. The gene also helps control the body's response to inflammation.

The results of these studies suggest that a TREM2 mutation raises the risk for developing Alzheimer's between three- and four-fold. However, the researchers acknowledge the need for additional studies to clearly establish R47H as the culprit.

Like many individuals with a parent who suffered from Alzheimer's, my husband has for years worried that each of his own memory lapses signaled the illness. His situation has been complicated by other conditions that cause short-term memory loss.

High-tech methods of studying genes like TREM2 bring with them a dilemma for individuals like him with a family history of certain illnesses. At the extreme, they face a quandary like that of individuals who had a parent with Huntington's disease.

In the case of Alzheimer's, knowing that not everyone with a mutation will develop the disease, should the offspring seek genetic testing? While the linking of a rare gene mutation to Alzheimer's is a step forward, considerably more research is needed before at-risk individuals like my husband feel enthusiastic about the discovery.

Vonda J. Sines has published thousands of print and online health and medical articles. She specializes in diseases and other conditions that affect the quality of life.

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