PTC Therapeutics (PTCT) said Monday that a phase 2 study of PTC518, or votoplam, in stage 2 and 3 Huntington's disease met its primary endpoint of reduction in blood Huntingtin protein levels at week 12.

The company said the study showed dose-dependent lowering of blood Huntingtin levels, with 23% at the 5mg dose for both stage 2 and stage 3 patients. Treatment may differ at the 10mg dose level based on the study results, according to the company.

Votoplam also demonstrated a favorable safety and tolerability profile across all dose levels and disease stages, PTC Therapeutics added.

Shares of PTC Therapeutics were down nearly 16% in recent premarket activity Monday.