"A rare, incurable brain disorder that resembles Parkinson's disease is caused by a misfolded brain protein called a prion, similar to the prions that cause mad cow disease, researchers reported on Monday.

The discovery adds to a very short list of human diseases linked to mutant prions, and suggests anyone doing brain surgery should take extra care, the researchers said.

The disease is called multiple system atrophy or MSA, and it affects somewhere between 15,000 and 50,000 Americans at any given time."

Maggie Fox reports for NBC News August 31, 2015. [2]