Rogue proteins, called prions, that cause mad cow and other brain-destroying diseases become toxic by latching on to the outside of cell membranes, say government scientists.

If researchers could break the fatty Velcro-like bond that anchors these prions, they might be able to treat the deadly illnesses, suggests the research published in the current issue of the journal Science. Scientists genetically engineered mice that lacked the fatty anchor that usually binds prions to the surface of cells. Then they injected the transgenic mice and regular mice with scrapie-causing prions. All 70 of the regular mice promptly got sick, but the 128 engineered mice remained healthy.