Winter seems to always be coming in Game of Thrones, but here in the real world, autumn is on the way. While the leaves will start falling in September, some biotech stocks could be set to soar.

Quite a few biotechs have important catalysts coming up in the next month. Three biotechs that could especially benefit from big news on the way are Alnylam Pharmaceuticals (NASDAQ:ALNY), PTC Therapeutics (NASDAQ:PTCT), and Zogenix (NASDAQ:ZGNX). Here's what they have in store in September.

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Alnylam Pharmaceuticals

Alnylam stock has soared in 2017, up close to 130% year to date. The biotech has reported positive results from a phase 2 study of experimental hemophilia drug fitusiran. Alnylam also received breakthrough-therapy designation for givosiran in treating acute hepatic porphyrias (a rare nervous system disease) and an influx of cash from partner Sanofi

But Alnylam should have the biggest news of all coming up in the next few weeks -- potentially even earlier than September. The biotech expects to announce top-line data from its late-stage study of patisiran in treating patients with hereditary ATTR (hATTR) amyloidosis. If those results are positive, Alnylam intends to file for regulatory approval by the end of 2017. 

There is a risk, however, that those results won't be as good as desired. Rival Ionis Pharmaceuticals reported concerning side effects in May from its late-stage study of inotersen, a potential competitor to patisiran. But if Alnylam reports solid efficacy without similar serious side effects, expect its stock to take off even more than it already has so far in 2017.

PTC Therapeutics

PTC Therapeutics is another biotech stock that's performed well in 2017, with shares up more than 70% year to date. Much of those gains have come in anticipation of an FDA advisory committee meeting scheduled for Sept. 28. The committee will review PTC's regulatory filing for Translarna in treating nonsense Duchenne muscular dystrophy (nmDMD). 

The results from this committee meeting should be quite interesting. PTC Therapeutics tried to file for approval of Translarna last year, but the FDA wouldn't accept the company's submission. The company decided to move forward anyway, filing under protest. 

Sarepta Therapeutics (NASDAQ:SRPT) already scored a controversial approval for its DMD drug, Exondys 51. With Sarepta's launch of Exondys 51 seemingly going pretty well, PTC Therapeutics wants its chance, too. A positive recommendation by the FDA advisory committee would be huge in the biotech's getting that chance. 

Zogenix

Zogenix hasn't soared like Alnylam and PTC Therapeutics have so far this year. In fact, the stock is barely above its price at the start of 2017. That could soon change, though.

The biotech expects to announce results from its late-stage study of ZX008 in treating Dravet syndrome by the end of September. Good news from that study should bode well for another pivotal late-stage study of the drug for the same indication that's close to completing enrollment. 

One company that will probably watch what happens with Zogenix intensely is GW Pharmaceuticals (NASDAQ:GWPH). GW Pharma should complete its regulatory filing for Epidiolex in October for treating Dravet syndrome and Lennox-Gastaut syndrome (LGS). Good news for ZX008 could mean that Zogenix and GW Pharma will compete directly against each other in the next few years. 

Sinking in September?

Investors should be aware, though, that each of these stocks could just as easily sink in September instead of soar. Clinical results and regulatory decisions aren't always positive. 

PTC Therapeutics probably faces the greatest risk. Filing under protest with the FDA isn't a high-probability move. Alnylam could also experience a similar fate as Ionis with its late-stage results. And even if Zogenix gets good news from its first late-stage study for ZX008, there's still another one to go before possibly filing for approval.

The possibility for huge rewards typically comes joined at the hip with the possibility of huge failure. Both exist for Alnylam, PTC, and Zogenix. 

Keith Speights has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Alnylam Pharmaceuticals and Ionis Pharmaceuticals. The Motley Fool has a disclosure policy.