What happened

Shares of gene therapy expert Abeona Therapeutics (NASDAQ:ABEO) closed down 12% on Friday after the company reported updated data from a phase 1/2 trial testing ABO-102, a treatment for a rare genetic disease called Sanfilippo syndrome type A, at the 21st annual meeting of the American Society for Gene and Cell Therapy.

So what

With shares having more than tripled over the past year, it may be more what Abeona didn't say in its update than what it did say that caused the stock to slip today.

But first let's start with the data it did present, which seemed promising enough. Abeona has been following some of the patients for 18 months and the treatment doesn't seem to have waned much -- as measured by biomarkers -- past the initial decline seen around 180 days. In the later cohorts of patients that were treated with higher doses of ABO-102, the 180-day data look better, although those patients haven't been followed as long, so we don't have data out to 18 months.

Doctor listens to boy's heart with a stethoscope

Image source: Getty Images.

Investors likely hit the sell button today because of a lack of any data beyond biomarkers and some data on liver size, which was also trending in the right direction. While biomarkers and liver size are likely to be a good indicator that the drug is working, patients' function, measured though neurocognitive scores, is ultimately what doctors and the parents of the kids who have Sanfilippo syndrome really care about.

Now what

Investors will just have to wait until the next update to (hopefully) get more information on the neurocognitive scores of the patients. Presumably investors will also get an update shortly about the plan for the next clinical trial for ABO-102, which should be designed to get the treatment approved.

In the meantime, Abeona has other programs. EB-101, a gene-corrected skin graft cell therapy for patients with recessive dystrophic epidermolysis bullosa, is ready to enter phase 3 development later this year. AB-101, a gene therapy that treats another type of Sanfilippo syndrome, produced positive, albeit early, data in February.

Brian Orelli has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.