Genome-wide imaging study identifies new gene associated with Alzheimer's plaques

Feb. 20, 2013 A study combining genetic data with brain imaging, designed to identify genes associated with the amyloid plaque deposits found in Alzheimer's disease patients, has not only identified the APOE gene -- long associated with development of Alzheimer's -- but has uncovered an association with a second gene, called BCHE.

A national research team, led by scientists at the Indiana University School of Medicine, reported the results of the study in an article in Molecular Psychiatry posted online February 19. The study is believed to be the first genome-wide association study of plaque deposits using a specialized PET scan tracer that binds to amyloid.

The research also is believed to be the first to implicate variations in the BCHE gene in plaque deposits visualized in living individuals who have been diagnosed with Alzheimer's disease or are at-risk for developing the disease. The enzyme coded by the BCHE gene has previously been studied in post-mortem brain tissue and is known to be found in plaques.

"The findings could recharge research efforts studying the molecular pathways contributing to amyloid deposits in the brain as Alzheimer's disease develops and affects learning and memory," said Vijay K. Ramanan, the paper's first author and an M.D./Ph.D. student at the IU School of Medicine.

The BCHE gene finding "brings together two of the major hypotheses about the development of Alzheimer's disease," said Andrew J. Saykin, Psy.D., Raymond C. Beeler Professor of Radiology and Imaging Sciences at IU and principal investigator for the genetics core of the Alzheimer's Disease Neuroimaging Initiative.

Scientists have long pointed to the loss of an important brain neurotransmitter, acetylcholine, which is depleted early in the development of the disease, as a key aspect of the loss of memory related neurons. The BCHE gene is responsible for an enzyme that breaks down acetylcholine in the brain. The other major Alzheimer's hypothesis holds that the development of the amyloid plaques is the primary cause of the disease's debilitating symptoms. As it turns out, the enzyme for which the BCHE gene codes is also found in significant quantities in those plaques.

"This study is connecting two of the biggest Alzheimer's dots," said Dr. Saykin, director of the Indiana Alzheimer Disease Center and the IU Center for Neuroimaging at the IU Health Neuroscience Center.

"The finding that BCHE gene variant predicts the extent of plaque deposit in PET scans among people at risk for Alzheimer's disease is likely to reinvigorate research into drugs that could modify the disease by affecting the BCHE enzyme or its metabolic pathway," he said. Some existing drugs inhibit this enzyme, but it is unclear whether this influences plaque deposits.

Overall, the results appear to offer scientists new potential targets for drugs to slow, reverse or even prevent the disease. Alzheimer's disease affects an estimated 5.4 million Americans and has proven resistant to treatments that do more than temporarily slow the worsening of symptoms.

Amyloid plaque deposits build up abnormally in the brains of Alzheimer's patients and are believed to play an important role in the memory loss and other problems that plague patients.

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Genome-wide imaging study identifies new gene associated with Alzheimer's plaques