What happened

Shares of clinical-stage biopharma Voyager Therapeutics (NASDAQ:VYGR) popped nearly 25% today after the company announced positive results for a phase 1b trial investigating the potential of its lead drug candidate to treat advanced Parkinson's disease. The early-stage gene therapy, VY-AADC01, demonstrated dose-dependent responses for several metrics including measures of daily activities, Parkinson's disease rating scales, and patient diaries. 

Management noted that the results will allow the company to initiate a pivotal phase 2/3 trial later this year and to dose the first patient in the first half of 2018. That was all the stock needed to find momentum after struggling for much of the last two years. As of 11:59 a.m. EDT, the stock had settled to a 16.7% gain.

A white-gloved hand holding a silver platter with a strand of DNA on it.

Image source: Getty Images.

So what

While this is good news for Voyager Therapeutics at this stage in development, investors should be cautioned that neurodegenerative diseases such as Parkinson's disease are notoriously complex and difficult to treat. Quite a few drug candidates over the years have demonstrated potentially promising results in early-stage trials only to flop once expanded to larger patient populations. We simply don't have a great understanding of the complex interactions between biology and brain function that point to obvious treatment mechanisms.

Voyager Therapeutics is hoping to overcome that with its novel adeno-associated virus, or AAV, gene therapy delivery system -- a technology that has caught the attention and investment of the largest pharmaceutical companies on the planet for various applications. It's certainly encouraging that the phase 1b trial results announced today were achieved with a single dose of VY-AADC01 and observed up to 24 months after drug administration.

That said, it was an open-label trial with only 15 patients divided equally into three cohorts. Although the trial design and low patient population are normal for neurodegenerative disease studies, they are two factors that have played a big role in the dismal track record of later-stage trials.

Now what

It's best for investors to take a nuanced approach to today's news. On one hand, Voyager Therapeutics has pretty encouraging results for its early-stage trial investigating a potential treatment for advanced Parkinson's disease. On the other hand, the complexity of the disease and nature of the trial design could result in ho-hum clinical results in later stages of development. As with many unproven and early-stage biopharmas, this remains a speculative investment.

Maxx Chatsko has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.