Alzheimer's Neuroscience

Alzheimer's is a devastating disease that robs people of memory and the ability to care for themselves. No one knows what causes it, but scientists have identified a number of genes associated with an increased risk of developing the condition.

Some of these genes are rare, yet almost everyone who has them will develop Alzheimer's. Other genes associated with inherited risk of developing Alzheimer's disease are more common, but don't necessarily mean the patient will be affected. Now an international team of researchers has identified another gene that's closely linked to developing Alzheimer's.

Doctor Peter St. George Hyslop from the University of Toronto led the study. He and his colleagues performed genetic testing on more than 6800 people, half with Alzheimer's disease and half without. Hyslop says his team found a gene they're calling SORL 1. Based on their testing, he believes that anyone with a variant of this gene is highly likely to develop Alzheimer's. "We think that about 60 percent or so of carriers will probably develop the disease, although that estimate will have to be refined by some future studies designed to look at how risky it is to have a variant in the SORL 1 gene," Hyslop says.

Hyslop hypothesizes that the presence or absence of the SORL 1 gene makes a difference in how the body processes a brain protein called APP. APP sparks the metabolic changes that lead to Alzheimer's.

Hyslop says scientists think that in the presence of the protein made by the SORL 1 gene, APP protein is less active. "In the absence of SORL1 protein, the APP protein is then allowed to go into the parts of a cell where it's chopped up and made into a fragment called amyloid, which causes Alzheimer's disease," he explains. "So basically what happens is the SORL 1 protein binds to APP and prevents it from being degraded into this toxic amyloid stuff that then causes Alzheimer's disease.

Hyslop says identification of this gene is a big part of the puzzle surrounding Alzheimer's disease. He says knowing about SORL 1 could make it a target for treatments of the disease. This could become more important as people around the world start to live longer lives.

Over the next 10 to 30 years, the number of individuals with Alzheimer's is going to double in industrialized societies, according to Hyslop, "simply because the proportion of people living into the age at risk for Alzheimer's disease is going to increase as the baby boomers age." But he says developing nations, which are probably even less able to deal with the problem, will also see more people suffering from Alzheimer's. "It's not just a problem of the rich nations, it's going to be a problem for everybody.

The study was published in this month's issue of the journal Nature Genetics.