The biggest loser today in the biotech space was Prana Biotechnology (NASDAQ:PRAN), down a massive 70% because its candidate Alzheimer's drug PBT2 failed its phase 2 trial. The drug failed not only to improve cognitive function, but it also failed to affect what it was intended to, by not reducing amyloid plaques in patients. The company is also testing the drug for Huntington's disease, but early data aren't encouraging for that indication.

In this video, Motley Fool health-care analyst David Williamson looks at the future of Prana Biotechnology. He discusses a statement from the company's CEO that it will continue to develop PBT2, and gives investors his opinion on the stock today. David also looks at where future efforts to treat Alzheimer's disease are going to be focused.