On Monday, for the third straight day, shares of CRISPR Therapeutics (CRSP 0.34%) stock declined, falling 11.2% through 11:30 a.m. ET -- which is kind of crazy when you think about it.

Just three days ago, CRISPR announced that the U.S. Food and Drug Administration (FDA) approved its Casgevy treatment for sickle cell anemia. Yet instead of rising, shares of this innovative biotech stock have fallen more than 19% over the last three days.

Why?

Introducing Casgevy

In case you haven't heard, on Friday the FDA approved the first-ever CRISPR-based gene-editing therapy for a major disease, afflicting 16,000 patients 12 years of age and older. (According to the National Institutes of Health, the market for this treatment may be even bigger: Approximately 100,000 Americans suffer from sickle cell disease -- and 20 million patients suffer from it worldwide.) 

CRISPR will bring the Casgevy therapy to market with help from partner Vertex Pharmaceuticals (VRTX -0.06%), and bring the potential to cure literal millions of people suffering from the disease and/or carrying the gene for it with a single, one-time transplant. CRISPR works by editing defective BCL11A genes in a patient's extracted stem cells and reintroducing them to the patient to cure the disease.

And yet, perversely, the fact that Casgevy is a one-time treatment may limit its revenue potential. Generally, curing a disease all in one go can be less lucrative for a company than merely treating the symptoms of a disease with repeated drug doses over weeks, months, or years. And in the wake of CRISPR's announcement, multiple stock analysts have been arguing over just how big of a deal Casgevy will turn out to be for the business.

In one note out today, for example, TD Cowen downgraded CRISPR to underperform and lowered its price target to $30, warning that Casgevy simply isn't a big enough revenue opportunity to justify CRISPR's $64 stock price. On the other hand, analysts from JMP Securities, Citigroup, and Barclays (among others) raised their price targets on CRISPR stock, using words such as "transformative" and "historic" to describe CRISPR's technology, as The Fly reports today.

Is CRISPR stock a buy?

Unfortunately for investors, we may need to wait a while to find out who's right on this one. On the one hand, Casgevy's FDA approval does not look like an immediately transformative event for the stock, which is on track for only $300 million or so in revenue this year (valuing it at about 17 times sales), and no profits. Indeed, analysts polled by S&P Global Market Intelligence predict that even with Casgevy approved, CRISPR won't turn profitable before 2026 at the earliest.

On the other hand, now that CRISPR's first gene-editing therapy treatment has been approved, others -- and others with bigger market opportunities -- may follow. Still, it remains to be seen just how "transformative" this "historic" technology will become in the future.

Unfortunately for investors, I'm afraid, this means CRISPR stock remains at best a speculative investment.