Aging leads to a decline in cellular fitness and loss of optimal protein function. Many age-related ailments, including Alzheimer's and Parkinson's diseases, are caused by protein aggregation, a result of errors in protein folding. Yet, the mechanisms underlying how aging causes proteins to aggregate has largely remained a black box. In new research published Jan. 19 in Nature, researchers at Stanford University have traced this problem to age-dependent impairment of the machinery that produces new proteins.