WHERE protection against Alzheimer’s is concerned, you can have too much of a good thing. If you inherit one copy of a particular gene mutation it seems to protect you from Alzheimer’s. With a copy from each parent, you may be in trouble.
of the Carlo Besta National Neurological Institute in Milan, Italy, and colleagues discovered the mutation in a 44-year-old man with signs of early-onset Alzheimer’s who didn’t have the usual gene mutations.
Both he and a younger sister with mild cognitive problems, have two copies of a mutation in a gene called APP, while relatives with just one copy of the mutation, including an 88-year-old aunt, seemed to be actively protected against the disease (Science, ).
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APP makes the protein A-beta, which can form clumps in the brain, blocking neurons from firing. But experiments showed that a mix of normal and mutant A-beta is less likely to clump than mutant protein or normal protein alone, which may explain why one copy of APP is protective.