NEW YORK ( TheStreet) -- A little-known factoid about Sarepta Therapeutics ( SRPT) that bothers me a bit: Sarepta, born AVI BioPharma, was incorporated in July 1980, making it one of the world's oldest biotechnology companies. That's a long time to be in business without ever developing a successful drug. But now, three decades and $320 million later, my colleague Adam Feuerstein thinks Sarepta may have finally hit the biotech jackpot. I agree with him that the company's lead drug, eteplirsen (formerly AVI-4658), shows promise as a treatment for Duchenne muscular dystrophy (DMD) -- a progressive disease that leaves patients wheelchair bound by their teens and dead shortly thereafter. Feuerstein, however, omitted some important risks to the Sarepta-eteplirsen story that deserve to be highlighted. Sarepta's eteplirsen induces the body to "skip" a section of the exon (a sequence of nucleic acids) that codes for dystrophin, a protein critical to muscle repair that is dysfunctional in patients with DMD. Think of a row of puzzle pieces with one missing. Eteplirsen facilitates creation of a semi-functional protein by hiding a mismatched puzzle piece (exon 51), which in turn enables matching puzzle pieces (sections of protein) on either side of the mutation to connect. Last month, Sarepta reported seemingly astonishing results from a tiny Phase IIb study of eteplirsen in DMD. After 36 weeks, four eteplirsen recipients walked 69.4 meters further in six minutes than four patients treated with 24 weeks of placebo and 12 weeks of drug. These results reached statistical significance despite the small number of patients enrolled. Importantly, the six-minute walk test (6MWT) results for all patients showed worsening, but the eteplirsen group did so more slowly. If these data hold at 48 weeks and patient dystrophin levels correlate with clinical response, Sarepta will have meaningfully de-risked the program and the stock could easily double from current levels. The company will present the 48-week data in mid-October at the World Muscle Society conference. Assuming positive results, Sarepta would likely start a pivotal trial by year-end. At the same time, Sarepta may seek early, accelerated approval of eteplirsen based on the tiny phase IIb study. Eteplirsen seems extremely intriguing but I'm a skeptic. Before investors' eyes register those cartoon-like dollar signs, let's review five potentially underappreciated risks to the Sarepta story.