Results published this week in the journal Nature Genetics identified five more genes associated with risk of developing Alzheimer’s, doubling the total number of genes known to be linked to the devastating disease. The two studies – one led by Paul Hollingworth and Julie Williams in Europe and the other by the Alzheimer’s Disease Genetics Consortium in the U.S. – analyzed DNA from more than 50,000 people of European ancestry. Altogether, the researchers identified five new genetic variants located near the ABCA7, MS4A4A, EPHA1, CD33, and CD2AP genes, which are each associated with a 10-15% increase or decrease in the odds of Alzheimer’s.
While the effects of these genetic variants may not be strong, their discovery offers additional clues about the biological underpinnings of the disease. Combined with previous studies (see Blog posts here and here), the genes implicated suggest that biological pathways involved in the immune system and in the transport of cholesterol-related molecules may be important in the development of the disease.
As reported in the New York Times on Sunday, one of the new studies’ authors, Dr. Richard Mayeux, said the findings would help “open up the field.”
Although the studies published this week help fill in some gaps in our understanding of Alzheimer’s, the risks associated with the newly identified variants are still dwarfed by the risk associated with the well-established Îµ4 variant of the APOE gene. If a person inherits the APOE Îµ4 variant from one parent, his or her risk is two to four times higher than the average person’s. If that person inherits it from both parents the risk rises to more than 10 times greater than average. But as with all complex, multi-factorial conditions such as Alzheimer’s, the presence of a variant does not mean a person will definitely develop the disease.
Currently more than 5.4 million Americans have Alzheimer’s. The Alzheimer’s Association estimates that this year alone the cost of the disease will top $183 billion.