The genetic story of Alzheimer's is becoming clearer--but not simpler. Researchers from Duke University Medical Center have identified three chromosomal regions that play a role in the onset of the disease. Variants in each genetic segment increase the risk of dementia during specific periods of life. By pinpointing these three regions, geneticists are closer to understanding who is likely to develop the disease--and when it may begin.
Two of the regions described in this study had not been found in previous studies. One of the newly identified regions determines the risk of very late-onset Alzheimer's, in which symptoms appear after the age of 80. The other increased susceptibility for early-onset disease--between the ages of 50 and 60.
For the study, published in the November issue of The American Journal of Human Genetics, Margaret Pericak-Vance, the director of the Duke Center for Human Genetics, and colleagues screened 437 families that included at least two members with Alzheimer's disease.
Using a process known as ordered subsets linkage analysis, researchers were able to identify which stretches of DNA were linked to the disease and correlate age of onset with the genetic pattern. One area of chromosome 15 was linked to families with very late-onset Alzheimer's; variations on a stretch of chromosome 2 were correlated with early-onset Alzheimer's. The genes that influence late-onset (between 60 and 75) lie on chromosome 15, a region that had been identified in a previous Duke study.