Why Did PTC Therapeutics Stock Fall On Monday Despite Mid-Stage Study For Huntington's Hits Primary Goal?

Core Insights - PTC Therapeutics announced results from the Phase 2 PIVOT-HD study of PTC518 (votoplam) for Huntington's disease, achieving its primary endpoint of reducing blood HTT protein levels with significant statistical significance [1][2] Study Results - The study demonstrated a reduction in blood HTT protein levels of 23% at the 5mg dose and 39% at the 10mg dose for Stage 2 patients, while Stage 3 patients showed a 36% reduction at the 10mg dose [4] - The treatment exhibited favorable safety and tolerability across all dose levels and disease stages, with no serious adverse events reported [5] Clinical Implications - There were observed dose-dependent trends in clinical scales for Stage 2 patients, including improvements in the Composite Unified Huntington's Disease Rating Scale (cUHDRS) and Total Motor Score (TMS) [4] - For Stage 3 patients, the 5mg dose showed favorable trends compared to placebo, indicating potential differences in treatment effects between stages [5] Long-term Data - 24-month treatment data indicated dose-dependent trends on cUHDRS, Total Function Capacity (TFC), and Symbol Digit Modalities Test (SDMT) subscales, with a notable lowering of plasma NfL levels at both 5mg and 10mg doses [6] Market Reaction - Following the announcement, PTC Therapeutics' stock fell by 18.60% to $40.65, reflecting investor concerns regarding the differing treatment effects observed in Stage 3 patients [5][7]