In the gene editing therapies space, there aren't any competitors being watched more closely than Vertex Pharmaceuticals (NASDAQ: VRTX) and CRISPR Therapeutics (NASDAQ: CRSP). The pair scored regulatory approval in the U.K. on Nov. 16 to market their first gene therapy developed in collaboration and investors have high hopes for a positive commercialization decision by the Food and Drug Administration (FDA) in the U.S. on Friday, Dec. 8.

But according to data described in a scientific journal article published in the middle of November, U.S. regulators may have reason to hesitate rather than grant a full approval. Here's what's going on and what the risks are for shareholders.

The gene therapy candidate made by Vertex and CRISPR Therapeutics is called exa-cel, and it's intended to treat sickle cell disease (SCD), a hereditary blood disorder that causes red blood cells to have a shape that's closer to a waxing crescent moon than their proper and iconic frisbee-like form. The sickle-cell-shaped blood cells become sticky and can cause blood flow issues, leading to pain and organ damage.

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Source Fool.com