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The results PTC released Monday give a fuller look at a Phase 2 study dubbed PIVOT-HD, which randomized Huntington’s patients to receive either placebo or one of two doses of the company’s drug, PTC518.

Treatment with PTC518 hit the study’s main goal, which measure blood levels of a protein called huntingtin at 12 weeks. That lowering was then maintained through one year, the updated data show.

Normally, huntingtin protein plays a variety of helpful functions in the brain. But when mutated in Huntington’s disease, the protein can clump together in a manner that’s toxic to nerve cells. Treatments like PTC518 are designed to degrade the nucleic acid blueprints that encode for the protein, thereby lowering levels.

However, linking PTC518’s effect on huntingtin protein to clinical benefit is harder to assess. For patients who were in an earlier, “Stage 2” of disease, the data showed “dose-dependent trends of benefit” versus placebo on a key scale measuring disease progression, PTC said. Among later, “Stage 3” patients, there were similar trends in the low dose group, but not among patients given the higher dose.

PTC said this might suggest a different treatment effect in Stage 3 patients versus Stage 2 individuals.

The company also presented interim, 24-month results that compared study participants to a natural history control group. There, too, PTC said the data hinted at a clinical benefit.

Favorable trends may not be enough to prove PTC518 is worthy of regulatory approval, though.

“There are no mentions of any associations between mHTT lowering and clinical outcomes, which we think is the most important aspect of this data readout,” wrote Leerink Partners analyst Joseph Schwartz in a client note Monday. “As a reminder, the [Food and Drug Administration] told [PTC] that while they were aligned with [huntingtin] lowering in principle to support an accelerated approval pathway, they wanted to see associations with [huntingtin] lowering and clinical outcomes.”

Kristen Kluska, an analyst at Cantor Fitzgerald, added in a separate note that she thought “the market reaction today seems more focused on the potential for [accelerated approval] vs. focusing on whether or not these data are de-risking.”

Shares in PTC were trading down by about 18% near mid-day Monday.

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