In this video as part of The Motley Fool's "Ask a Fool" series, Fool health-care analyst David Williamson takes a question from a Fool reader, who asks, "What's your Foolish take on Prana Biotech (NASDAQ:PRAN)?"

While there is a huge amount of investor enthusiasm surrounding the company and its drug PBT2, which would target Alzheimer's disease and Huntington's disease, that's exactly the source of David's concern about the drug and Prana itself. Any successful treatment to emerge for either of these indications would be a blockbuster, but real success has been extremely limited here, as these disorders are proving extremely difficult to crack.

David cites an article from Summer Street today coming out with a negative note on Prana, in which author Adam Feuerstein said he was "not enthusiastic about the drug's purported mechanism," and "not impressed with the data to date." Shares sold off dramatically today as a reaction to the article.

David warns that at the moment, Prana for all intents and purposes is defined by its PBT2 drug, and that investors should really consider whether the risk is worth the reward here, given how high he sees the likelihood of failure.