A gene that causes the rare, early-onset form of Alzheimer's disease can also carry a mutation that produces the opposite effect, staving off the devastating illness, scientists announced on July 11, 2012.
"Less than 1 percent of the population has these alleles," or DNA variants, said Dr. William Thies, chief medical and scientific officer of the
Alzheimer's disease is defined by the presence of sticky plaques, composed of a peptide called amyloid beta. Amyloid beta comes from a larger protein called amyloid precursor protein, or APP. Over the last two decades, scientists have identified some two dozen mutations in the APP gene that cause early-onset Alzheimer's, which strikes before age 65.
A novel mutation in the APP gene does the opposite, scientists led by Dr. Kari Stefansson of privately held deCODE Genetics in Reykjavik found when they sequenced the genomes of 1,795 Icelanders.
Those 85 or older who have the beneficial mutation are 81 percent less likely to develop the neurodegenerative disease than others in that age group, the team found. The variant also makes developing Alzheimer's four times less likely across all age groups.
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