Alzheimer's 'usually caused by genes' - study

A new study of nearly 12,000 twins shows that Alzheimer's has a genetic cause in up to 80 percent of cases, researchers said on Monday.

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The study, which used the unique twin registry at Stockholm's Karolinska Institute, raises doubts about the role of environmental factors in contributing to the disease, said Margaret Gatz, professor of psychology at the University of Southern California in Los Angeles and lead author of the report.

"In essence what we're doing is taking the folks who would have formerly been called sporadic (environmental), and testing how important genetic influences are...and we're finding genetic influences are tremendously important," Gatz said in a statement.

"It does suggest that there is an underlying genetic basis," she said.

According to the study's data, which was based on the largest sample ever under taken in research of the disease, genetic influence accounted for 79 percent of Alzheimer's risk, the report said.

The other 21 percent of risk was due to environmental causes, the study said.

The sample for the study was based on 11,884 twins in Sweden over the age of 65. The Swedish Twin Registry is the largest and most complete register of its kind in the world, and is currently being used to study diseases including osteoporosis, schizophrenia, cardiovascular disease, Parkinson’s, autism and chronic fatigue syndrome.

Gatz led an international team of researchers from Swedish and US universities in a project funded by grants from the National Institute of Aging and the Alzheimer's Association.

She said, however, that environmental factors could not be dismissed. "This doesn't mean that environment is not important. Environment may be relevant not only for whether but also for when one gets the disease."

More than 24 million people worldwide suffer from Alzheimer's or similar conditions and the number is set to double every 20 years, said a study published last month in British medical journal The Lancet.

AFP/The Local