Study Suggests Genetics as a Cause, Not Just a Risk, for Some Alzheimer's

Pam Belluck reports via the New York Times: Scientists are proposing a new way of understanding the genetics of Alzheimer's that would mean that up to a fifth of patients would be considered to have a genetically caused form of the disease. Currently, the vast majority of Alzheimer's cases do not have a clearly identified cause. The new designation, proposed in a study published Monday, could broaden the scope of efforts to develop treatments, including gene therapy, and affect the design of clinical trials. It could also mean that hundreds of thousands of people in the United States alone could, if they chose, receive a diagnosis of Alzheimer's before developing any symptoms of cognitive decline, although there currently are no treatments for people at that stage. The new classification would make this type of Alzheimer's one of the most common genetic disorders in the world, medical experts said. "This reconceptualization that we're proposing affects not a small minority of people," said Dr. Juan Fortea, an author of the study and the director of the Sant Pau Memory Unit in Barcelona, Spain. "Sometimes we say that we don't know the cause of Alzheimer's disease," but, he said, this would mean that about 15 to 20 percent of cases "can be tracked back to a cause, and the cause is in the genes." The idea involves a gene variant called APOE4. Scientists have long known that inheriting one copy of the variant increases the risk of developing Alzheimer's, and that people with two copies, inherited from each parent, have vastly increased risk. The new study, published in the journal Nature Medicine, analyzed data from over 500 people with two copies of APOE4, a significantly larger pool than in previous studies. The researchers found that almost all of those patients developed the biological pathology of Alzheimer's, and the authors say that two copies of APOE4 should now be considered a cause of Alzheimer's -- not simply a risk factor. The patients also developed Alzheimer's pathology relatively young, the study found. By age 55, over 95 percent had biological markers associated with the disease. By 65, almost all had abnormal levels of a protein called amyloid that forms plaques in the brain, a hallmark of Alzheimer's. And many started developing symptoms of cognitive decline at age 65, younger than most people without the APOE4 variant.

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