The affected brain cells start the complex job of splitting in two, only to inexplicably grind to a halt partway through the process. Stuck with a toxic extra copy of the genetic material they had intended to pass along to their offspring, the now overloaded and grossly damaged cells linger for months, their vital communication links to nearby neurons slowly withering. The brain cells' eventual demise, the researchers believe, is due to the excess genetic baggage they're carrying from their ill-fated attempt to spawn. It is a novel explanation for the advancing siege of cell death that robs Alzheimer's patients of memory and sanity. Previously, some scientists had thought that the sticky clumps and tangled fibers that litter the brains of Alzheimer's patients were directly responsible for killing nerve cells.
Neurons are highly resistant to division.
And they get to make that mistake only once. We've always been curious why certain cell types are vulnerable to death in Alzheimer's. This study has given us a possible mechanism for why this happens. Most of our cells reproduce themselves regularly, to replace worn-out cells or allow the body to deal with injury, disease or extra demands. Muscle cells, for example, churn out copies in response to exercise.