What: Shares of the clinical-stage biopharma Catalyst Pharmaceuticals (NASDAQ:CPRX) climbed by 15% on heavy volume today after the company announced top-line results from a Proof-of-Concept study for its experimental Tourette's disorder drug vigabatrin (CPP-109). Per the press release, one out of four patients taking the drug exhibited a clinically and statistically significant reduction in tics associated with the disorder, and two other patients experienced around a 25% decline in tics but without a clear cut clinical response.

So what: Although this is an exceedingly small study and only a single patient may have responded to treatment, Catalyst's management, along with the study's primary investigators, noted that these were individuals that had failed other therapies prior to taking part in this study (treatment refractory). So, vigabatrin, or its more potent analogue CPP-115, could turn out to be a viable therapeutic option for treatment refractory patients suffering from this debilitating and rare disorder. 

Now what: Based on these initial results, Catalyst will move forward with their plans to develop CPP-115 in the treatment refractory setting for Tourette's disorder, which is reportedly a safer and more potent GABA-AT inhibitor than vigabatrin. Even so, you may want to play it safe with this small-cap biopharma for the time being, given that this double-digit move is being driven by an extremely small, open-label study with mixed results. After all, three-fourths of the patients in the study didn't respond to vigabatrin in a clinically meaningful way.