What's happening: Shares of bluebird bio (BLUE -0.29%), a clinical-stage biotechnology company with a focus on gene therapy, were shot down today on higher than normal volume, falling by more than 12% at one point today before slightly rebounding to a loss of just over 10%.

Why it's happening: While there doesn't seem to be any particular news today from bluebird that justifies such a strong move, it was a bad day for the biotech sector in general thanks in large part to a tweet issued by presidential hopeful Hillary Clinton. In the tweet, Clinton expressed her outrage over an article by the New York Times that referenced a huge price jump in a decades-old specialty drug, noting that her plan to curb costs would be released tomorrow.

The biotech sector, as measure by the iShares Nasdaq Biotechnology ETF (NASDAQ: IBB), fell more than 4% as a result of this tweet, and it appears that bluebird simply got hit especially hard as a result -- which is not terribly surprising since bluebird is a rather speculative investment and therefore prone to dramatic swings.

Even though other democratic presidential candidates seem to have a focus on curbing costs related to prescription drugs, I have a hard time getting too worked up about their potential impact on companies like bluebird that focus on treating rare diseases. Bluebird's lead product candidate, called LentiGlobin, is being studied as a treatment for Beta-thalassemia and Severe Sickle Cell Disease. The combined patient population for these diseases is well under 200,000 patients in both Europe and the U.S. If approved, it's likely that LentiGlobin would come with a steep price tag, but given the size of the market it's hard for me to see a huge amount of pushback over the pricing. Without a strong financial incentive in place to entice companies to devote resources to creating treatments for rare diseases, funding for this costly research would likely fall hard, which I'm guessing is not an effect any of these candidates wants to appear to have their name associated with. 

As bluebird is still in the clinical stage, there are plenty of risks associated with an investment in the company, so the market will naturally be skittish whenever news like this happens, but if you were bullish on bluebird's prospects yesterday, I see no reason to change your tune today.