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---------------------------------------------------------------------------- Scientists pinpoint role of Alzheimer's genes ---------------------------------------------------------------------------- BOSTON (September 4, 1997 5:51 p.m. EDT) - A defect in the ability of a cell to properly parcel out its genetic material when it replicates itself may be an underlying cause of most inherited cases of Alzheimer's disease, according to a new study. Five Harvard University researchers report in Friday's issue of the journal "Cell" that they have uncovered the tasks performed by two chunks of genetic material, known as presenilin 1 and presenilin 2. Those genes, which have been implicated in the familial form of Alzheimer's, help govern a cell's ability to make copies of its genetic material and send a complete copy to opposite ends of the cell just before it splits in two. Alzheimer's, a brain disease that can lead to confusion, memory loss and speech problems, often starts in later middle life and is estimated to afflict more than 10 percent of those over 65 years of age. When presenilin 1 or presenilin 2 is defective, the genetic material is not divvied up properly and the two cells created from the original may not be able to function normally. The same inability to correctly divide the genetic material is responsible for Down's syndrome, where an extra copy of one of the body's chromosomes produces a distinctive pattern of birth defects, including varying degrees of retardation. Huntington Potter, leader of the Harvard team, said he has long suspected a link between Down's and Alzheimer's because people with Down's syndrome always develop Alzheimer's when they are in their 30s or 40s. The same chromosome, number 21, responsible for Down's syndrome also carries the genetic code for a telltale protein seen in the brain of Alzheimer's patients. Down's syndrome, which occurs in about 1 in 600 to 650 live births, is marked by mental retardation and physical defects. The evidence for Down's syndrome shows up in nearly every cell in the form of a third, unwanted copy of chromosome 21. Potter said the new research supports the idea that people without Down's syndrome who inherit Alzheimer's disease may developed the extra chromosome in some of their cells but not others because the defect appears later in the person's development. "Instead of occurring in every cell of the body because the chromosome segregation went wrong during the development of the egg, it occurred during the growth of the individual, so only a small percentage of cells had three copies of the chromosome," Potter said. "This would then cause Alzheimer's disease, but at a later stage because of the fact that you only have a few cells in the body that have this genetic defect." In a separate preliminary study, Potter and Lisa Geller of Harvard have found that the number of skin cells with an extra copy of chromosome 21 is three times higher in people with Alzheimer's disease than it is in healthy individuals of the same age. By GENE EMERY, Reuters Copyright 1997 Nando.net Copyright 1997 Reuter Information Service <http://www.nando.net/newsroom/ntn/health/090497/health10_27023_noframes.html> ---------------------------------------------------------------------------- [log in to unmask]