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Alzheimer gene discovery points to possible cause

A gene mutation whose discovery was announced Wednesday triples the risk for Alzheimer’s disease.  It is a headline that might sound frightening but shouldn’t evoke fear.

The mutation in the gene called TREM2 is rare, occurring in about 1 in 150 people.  By comparison one in five people carry a form of a different gene called APO-E that also triples the risk.  One in 50 carries a form of APO-E that raises risk 13 times. APO-E’s relation to Alzheimer’s was discovered in 1993.   So in terms of public health implications, TREM2 is a small player, and is one of an ever growing list of genes implicated in Alzheimer’s

Still, the research from two teams, one headed by  Dr. Kari Stefansson at DeCode Genetics in Iceland and the other by Dr. John Hardy of University College London and both published in the New England Journal of Medicine, is critically important science that may yield clues about the causes of Alzheimer’s disease and the search for better treatments. 

TREM2 in its normal form plays a role in inflammation, the body’s response that sends white blood cells to destroy invading germs and diseased tissue.  The mutation cuts the ability to mount an inflammatory response, so it ispossible the ability to fight other diseases is tied up with the risk for Alzheimer’s.  For more than a century pathologists have noted a buildup of white blood cells in the brains of people who died from Alzheimer’s.

No one is sure what causes Alzheimer’s, which already affects more than 5 million Americans and costs the U.S, economy more than $148 billion a year, according to the Alzheimer’s Association. The numbers are projected to worsen as the baby boomer generation ages. There is no treatment and no cure.

The leading contender as the main cause of Alzheimer’s is the accumulation of plaques of protein called amyloid-beta.  It is likely that the inflammatory response is attempting to keep that buildup at bay. Last July, Stefansson’s team discovered a different gene mutation, even more rare, that actually protects against Alzheimer’s. That, too, was important science because that gene is responsible for production of amyloid-beta.  So it both supports the hypothesis about the cause and leads to ideas about how to make drugs to stop it.

Stefansson established DeCode in 1996 to find disease-causing genes in Iceland, a country with a homogenous population and national health service with excellent records.  At first it was a profit making venture, but despite an impressive record of locating genes associated with several diseases, the company was forced to declare bankruptcy in 2009.  It continues as a non-profit enterprise.  The two Alzheimer’s genes discovered in the past few months illustrate why the genetic research is so important even though it does not lead to immediate public health benefits or profits.

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