Mounting evidence has suggested that toxic proteins that cause Alzheimer’s, Parkinson’s, and other neurodegenerative diseases spread from neuron to neuron in a slow crawl through the brain.

That news sparked some concern among the media and the general public: Could these proteins pass between people, too?

Highly unlikely, concluded scientists led by John Trojanowski, University of Pennsylvania, in a paper in the February 4 JAMA Neurology. Data from a large cohort of patients treated with human growth hormone from cadaver preparations suggest that injection of brain material does not spread Alzheimer’s (AD) or Parkinson’s disease (AD).