Game on, BioMarin Pharmaceuticals (BMRN) .

A panel of outside experts convened by the U.S. Food and Drug Administration will spend all day Tuesday reviewing drisapersen, BioMarin's experimental drug for Duchenne muscular dystrophy (DMD).

Investors have been debating the future of drisapersen for years, so it's exciting to be finally on the cusp of a definitive outcome for the drug. Obviously, the people suffering from DMD and their families have even more at stake. An FDA review of drisapersen made public Friday was highly critical, concluding that efficacy data from three clinical trials "does not reach the level of substantial evidence" necessary for approval. The FDA reviewers also raised concerns about drisapersen's safety.

BioMarin will need to work extra hard at today's FDA advisory panel to defend drisapersen against the agency's negative review. The independent experts on the panel will be weighing drisapersen's efficacy and safety data in the context of Duchenne being a fatal disease with no currently approved treatments. The panel might also be swayed by two hours of testimony from DMD patients, their families and advocates, most, if not all, will be urging the FDA to approve drisapersen.

The outcome of Tuesday's FDA panel is also important to Sarepta Therapeutics (SRPT) , which has its own, competing DMD drug under FDA review. 

Duchenne muscular dystrophy is a rare, genetic disease caused by a mutation on the X chromosome. This mutation, in turn, results in malfunctioning or missing dystrophin, a protein necessary for proper muscle function. Boys with DMD (the disease almost always strikes boys) suffer from progressive weakening of their muscles. By around 12, they can no longer walk. The disease also affects breathing and heart function. Few DMD patients live beyond 30.

Since DMD is caused by a mutation in the gene encoded to make dystrophin, one approach to treating the disease is to design a drug capable of removing or "skipping over" the damaged section, or exon, of the gene. Doing this allows the gene to produce dystrophin that is partially functional and stabilize muscle function.

Drisapersen is an "exon-skipping" drug designed to target the defect at exon 51 on the dystrophin-producing gene. Approximately 13% of the 30,000 DMD patients in the U.S. have a defect at exon 51 which could be treated with drisapersen.

 

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.