Today’s News: A Good Mutation that Prevents Dementia

Most genetic mutations found in medical research are bad – they increase risk of some condition – or at best offer trade-offs.  Today's issue of Science had a fascinating paper about a genetic mutation that seems to prevent people from developing Alzheimer's Disease. The study was done by a company in Iceland called DeCode Genetics. Scientists there found the mutation by combing through the DNA of 1,795 Icelanders. The beauty of working with this sample is that people in Iceland also have very complete medical records and genealogies, so the researchers can compare health status, genes and patterns of inheritance.

What they found was that about one in 10,000 people carry this protective mutation – a spelling error in a gene that's involved in the production of a protein called beta amyloid. Other mutations in that same gene can lead to a form of early onset Alzheimer's disease that runs in families.

Greg Petsko, a biologists at Brandeis University, said there were a couple of points that the news reports didn't make. One was that people with this protective mutation still had about half of the normal amount of beta amyloid. Knowing that helps those developing drugs by showing how much of a reduction would protect people from the disease. Before this finding, they didn't know whether they'd need to get rid of 90 percent, or perhaps 99 percent of the beta amyloid do make a difference.

Beyond that, he said, the mutation probably has an influence on people's brains through their lives, and so to imitate its effect with a drug, doctors may need to give it as a preventative measure while patients are young. Dr. Petsko also noted that there appeared to be now downside to the mutation – a good indication that reducing beta amyloid is safe.

Unfortunately for us, natural selection hasn't done much to spread this mutation, since its influence isn't felt until late in life. Such late-acting genes have little effect on our ability to produce surviving offspring.
Read more in this story from today's New York Times