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. Last Updated: 07/27/2016

Scientists Find Gene Linked to Alzheimer's Disease

WASHINGTON -- Scientists said Sunday that they had pinpointed a new gene linked to Alzheimer's disease, the incurable brain disorder that is the top cause of dementia in the elderly.

Abnormalities in a gene called SORL1 increased the risk for the disease. This finding could help scientists develop new treatments, the researchers reported in the journal Nature Genetics.

The researchers looked at DNA samples from 6,000 people from four ethnic groups: Caribbean-Hispanics, North Europeans, black Americans and Israeli-Arabs. They found certain variations of SORL1 more often in people with late-onset Alzheimer's disease than in healthy people.

The late-onset form, affecting people aged 65 and up, represents about 90 percent of Alzheimer's cases. The rarer, early-onset form affects people from ages 30 to 65. Only one other gene, called ApoE4, has been identified as a risk factor for late-onset Alzheimer's. It was identified in 1993.

"This appears to be the fifth Alzheimer's disease gene, and there are likely to be other important genetic variants that need to be identified before the entire picture is complete," Dr. Richard Mayeux of Columbia University Medical Center in New York said.

Many scientists think Alzheimer's begins with the buildup in the brain of a gooey material called amyloid that clumps together to form plaques. That material stems from a protein called amyloid precursor protein, or APP.

SORL1 controls the distribution of APP inside nerve cells of the brain. When working normally, the gene prevents APP from being degraded into a toxic byproduct called amyloid beta peptide. When SORL1 is deficient, it allows more of the bad amyloid beta peptide to accumulate, fostering amyloid plaques.

Alzheimer's is a complex disease that gradually destroys a person's memory and ability to learn, reason, make judgments, communicate and carry out daily activities. Scientists have struggled to understand the biology of the disease and its genetic and environmental causes.

Dr. Peter St. George-Hyslop, director of the Center for Research in Neurodegenerative Diseases at the University of Toronto, said it was premature to say what percentage of cases of late-onset Alzheimer's disease could be attributed to SORL1. ApoE4, which also may be involved in the production of amyloid plaques, has been linked to about 20 percent of late-onset Alzheimer's cases.

The disease first affects parts of the brain controlling memory and thinking, but as it advances it kills cells elsewhere in the brain. Eventually the loss of brain function will prove fatal.