Scientists have made an artificial prion that can, by itself, produce a deadly infectious disease in mice and may help explain the roots of mad cow disease.

The findings are strong evidence for the “protein-only hypothesis,” the controversial idea that a protein, acting alone without the help of DNA or RNA, can cause certain kinds of infectious diseases.

Alzheimer’s disease, Parkinson’s disease, Type 2 diabetes and at least two dozen other human disorders may be caused by misshapen proteins, according to Dr. Stanley Prusiner, a neurology professor at the University of California, San Francisco, who led the new study.