The researchers identified 29 variants that mark relatively short segments of DNA where disease-causing changes could lie. The study did not, however, identify specific genetic changes that result in Alzheimer's. The study involved 14 collaborating institutions in North America, Europe and Asia, and 6,000 individuals who donated blood for genetic typing.
"We do not fully understand what causes Alzheimer's disease, but we know that genetic factors can play a role," says National Institute on Aging (NIA) director Richard J. Hodes, M.D. "Scientists have previously identified three genes, variants of which can cause early onset Alzheimer's, and one that increases risk for the late onset form. This discovery provides a completely new genetic clue about the late onset forms of this very complex disease."
Scientists think that in Alzheimer's disease, amyloid precursor protein, or APP, is processed into amyloid beta protein fragments that make up plaques in the brain. The researchers began their search for genetic influences amid a group of proteins that transport APP within cells, looking for small changes, or "misspellings," in seven genes involved in moving APP within cells.
To start, the scientists combed two large data sets of genetic information from families in which more than one person has Alzheimer's disease. They were soon able to see that many of the families with Alzheimer's had variations in the SORL1 gene but not consistently in any of the other six genes. "We are seeing the gene implicated in multiple data sets, across ethnic and racial groups," says Lindsay Farrer, Ph.D., of Boston University. He adds that the group was "encouraged and excited" by cell biology experiments that demonstrate SORL1's role in production of beta amyloid fragments.
MEDICA.de; Source: National Institute on Aging