What: Shares of the antisense drugmaker Ionis Pharmaceuticals (NASDAQ:IONS) rose by as much as 10.3% yesterday on heavier-than-normal volume. The stock finished the day up 9.43%, making it one of the top-performing biotech stocks during a particularly volatile trading session for the entire industry. 

So what: Despite the stock's strong finish yesterday, Ionis, and many of its biotech peers, actually started the session off by dropping by nearly 10%. While there wasn't a specific catalyst underlying this initial downward move, it is telling that these stocks --along with the iShares Nasdaq Biotechnology ETF (NASDAQ:IBB) -- all sank right around 10:02 am ET. Making this volatility even more interesting, the iShares Nasdaq Biotechnology ETF rebounded thereafter in a similar manner to Ionis, gaining more than 4% for the day.   

IBB Price Chart

IBB Price data by YCharts.

So, what's going on in biotech? Although it's hard to pin down an exact cause, my belief is that these wild swings are partly due to major funds rotating out of the high-risk biotech industry, combined with the influence of high-frequency trading, or HFT. After all, it's sort of odd that most of the selling across the entire industry occurred at a specific time, implying the hand of HFT at work.

Now what: These unpredictable swings in share price -- that have no obvious material basis -- might be hard to stomach, but they shouldn't deter investors from buying quality biotech stocks (like Ionis) for the long term. Ionis presently boasts over 38 ongoing clinical trials, including several blockbuster candidates like its next-generation cholesterol drug, Volanesorsen. That's why I think it's important to ignore this short-term noise, and instead, keep the big picture in mind going forward.  

George Budwell owns shares of iShares NASDAQ Biotechnology Index (ETF). The Motley Fool recommends Ionis Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.