Alnylam Pharmaceuticals Reports 60% to 64% Huntingtin Reduction in Brezosiran Trial

04:35 AM EDT, 10/23/2026 (MT Newswires) -- Alnylam Pharmaceuticals (ALNY) reported positive initial phase 1b results for brezosiran, showing 60% to 64% mean reductions in cerebrospinal fluid mutant huntingtin levels at three months in the highest dose group evaluated to date, the company said Friday. The study showed dose-dependent mutant huntingtin reductions of up to 83%, with an encouraging safety profile over up to 12 months and no dose-dependent increases in inflammatory markers, neurofilament light chain or brain ventricular volume, the company said. Brezosiran targets both full-length mutant huntingtin and the shorter HTT1a protein, with durable reductions supporting the potential for twice-yearly dosing in an extension study lasting up to 36 months, the company added. Alnylam plans to launch a placebo-controlled pivotal study in 2027 and discuss the program at its RNAi Roundtable on Oct. 26. Alnylam Pharmaceuticals shares were down 1% in premarket activity.