A rare mutation that alters a single letter of the genetic code protects people from the memory-robbing dementia of Alzheimer's disease, according to a new study. The DNA change may inhibit the buildup of β amyloid, the protein fragment that accumulates in the hallmark plaques that form in the brains of Alzheimer's patients. Other researchers say the findings are intriguing but not hugely surprising. They fit well, in fact, with current thinking about Alzheimer's disease.

The newly identified mutation affects a gene called APP, which encodes a protein that gets broken down into pieces, including β amyloid. Previously, researchers have identified more than 30 mutations to APP, none of them good. Several of these changes increase β amyloid formation and cause a devastating inherited form of Alzheimer's that afflicts people in their 30s and 40s—much earlier than the far more common "late-onset" form of Alzheimer's that typically strikes people their 70s and 80s.
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