Mutation limits Alzheimer's disease, other cognitive decline

Most people who live long enough undergo a gradual decline in their mental abilities. For those who suffer from Alzheimer's disease, however, the decline is radical; in some genetic forms of the disease, it can even strike middle-aged victims. This has led many to conclude that Alzheimer's pathology is distinct from that of age-related decline. But a new study has found a single mutation that appears to protect people from both Alzheimer's and cognitive decline, leading its discoverers to suggest that Alzheimer's is just an extreme form of aging.

The work relies on a rather distinctive resource: the population of Iceland. The country has received very few immigrants over the years, and has maintained detailed birth records for most of its citizens, making it easy to track most people's genetic legacy. It also has a full national health system that keeps track of the population's ailments. All of which make it an excellent place to track down the genetics behind a variety of health ailments.

deCODE Genetics was founded to take advantage of this resource, and successfully scanned the DNA of Icelanders using DNA chips, finding parts of the genome that were associated with things like heart disease and diabetes. Now, deCODE actually has sequence data on the entire genome of nearly 1,800 Icelanders to add to the DNA chip data; because of the detailed birth records, it can infer the genotypes of almost 300,000 people. In the latest paper to use the deCODE data, researchers have turned their attention to Alzheimer's disease.

Most genetic studies of Alzheimer's have focused on the mutations associated with the rare, early onset forms of the disease. In the new study, an international team that included deCODE members decided to search for variants associated with the more common, late onset form. Rather than finding a variant associated with heightened risk, however, they found one that appeared to protect its carriers from Alzheimer's. In the elderly without Alzheimer's, 0.62 percent of the population carried the mutation; in the Alzheimer's group, only 0.13 percent did.

http://arstechnica.com/science/2012/07/mutation-limits-alzheimers-disease-other-cognitive-decline/