Researchers have identified a second gene responsible for the most common form of Alzheimer’s disease, a development that may make it easier to screen for, and ultimately treat, this devastating brain condition, a study released Sunday said.
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 the same age.
The Alzheimer’s victims also had a strikingly low level of the SORL1 protein in the blood compared with healthy people — less than 50 percent of the level seen in 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, drives the protein to a part of the cell where it is recycled.
But in people with the gene variants, the gene appears to drive APP to another region of the cell where it accumulates and is degraded into amyloid plaques — the abnormal sticky proteins that gum up the brain of Alzheimer’s victims, the researchers said, citing laboratory experiments.
"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, co-director of the Taub Institute for Research on Alzheimer’s Disease and the Aging Brain, and one of the authors of the paper.
"SORL1 is another critical piece of the Alzheimer’s disease puzzle."
The 1990s was a fruitful decade for Alzheimer’s research. In 1993, US scientists identified the first genetic marker for late-onset Alzheimer’s in the form of ApoE4, and two years later Canadian researchers linked two genes to the aggressive early-onset form of the disease.
But a decade later, effective treatments for the progressive brain disease are still lacking, and the only definitive way to diagnose the illness is by an autopsy.
Drug 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.
Some of those drugs are in clinical trials and should be on the market in five to 10 years, but it is a race against the clock as the number of Alzheimer’s cases is predicted to surge with the graying of the population.
In the United States alone, 4.5 million people have been afflicted with the memory-sapping illness, and the prevalence is expected to double in the next 25 years.
