Some people who were treated with cadaveric human growth hormone (cHGH) and who developed Creutzfeldt–Jakob disease also developed deposits of amyloid-β protein (Aβ), pathology more commonly associated with Alzheimer disease (AD). As AD brain homogenates can seed Aβ deposits in mice, the authors hypothesized that the cHGH used might have been contaminated with Aβ as well as prions. Indeed, certain cHGH batches were contaminated with Aβ40 and Aβ42, and intracerebroventricular injection of these contaminated samples into mice expressing a mutant humanized amyloid precursor protein resulted in Aβ plaque formation and development of cerebral Aβ–amyloid angiopathy.