CHICAGO: A second gene responsible for the most common form of Alzheimer's disease has been identified by U.S. and Canadian researchers.
"The importance of the finding is that it opens new pathways to explore the cause of the disease, as well as potential targets for treatment," said Richard Mayeux of Columbia University's Taub Institute for Research on Alzheimer's Disease and the Ageing Brain, and one of the authors of the study.
In genetic studies involving some 6,000 volunteers, the researchers discovered that variants of the gene SORL1 were more common in people with late-onset Alzheimer's than in healthy people of the same age.
Additionally, the Alzheimer's sufferers had less than 50 per cent as much of the protein produced by SORL1 in their blood compared with the healthy group.
In healthy people, SORL1, which is a 'traffic cop' regulating the flow of amyloid precursor protein (APP) inside nerve cells in the brain, sends APP to a part of the cell where it is recycled.
But in people with the gene variants, the protein produced by the SOR1 gene appears to drive APP to another region of the cell where it accumulates and is degraded into amyloid plaques. Plaques, according to the researchers, are the abnormal sticky proteins that gum up the brain of Alzheimer's victims. "SORL1 is another critical piece of the Alzheimer's disease puzzle," said Mayeux.
In 1993, U.S. scientists identified the first genetic marker for late-onset Alzheimer's and two years later Canadian researchers linked two genes to the aggressive early-onset form of the disease.
But a decade on, effective treatments for the progressive brain disease are still lacking, and the only definitive way to diagnose the illness is by autopsy.
Pharmacuetical companies are scrambling to develop drugs, many of them targeting the beta-amyloid protein fragments that are considered a prime suspect in the nerve cell death that is a feature of the disease, according to the Alzheimer's Association in Chicago, Illinois.
Some of those drugs are in clinical trials and should be on the market in five to 10 years, but it's a race against the clock as the number of Alzheimer's cases is predicted to surge with the greying of the population.
In the United States alone, some 4.5 million people have been afflicted with the memory-sapping illness, and the prevalence is expected to double in the next 25 years.
The authors of this study, published today in the British journal Nature Genetics, said they hoped that this discovery would speed the search for drug therapies, and once they are in place, help identify people at risk for the disease.
"Right now, there are questions about the value of screening people for the disease, because we can't do much about it. All that changes if there are effective therapies that can prevent brain damage occurring," said co-author Peter St. George-Hyslop, of the Centre for Research in Neurodegenerative Diseases at the University of Toronto in Canada.
