What do "mad cows", people with neurodegenerative diseases, and an unusual type of inheritance in yeast have in common? They are all experiencing the consequences of misfolded proteins. ... In humans the consequences can be deadly, leading to such devastating illnesses as Alzheimer's Disease. In one case, the misfolded protein is not only deadly to the unfortunate individual in which it has appeared, but it can apparently be passed from one individual to another under special circumstances – producing infectious neurodegenerative diseases such as mad-cow disease in cattle and Creutzfeldt–Jacob Disease in humans.