RNAi (RNA interference) therapeutics company Alnylam Pharmaceuticals Inc (Nasdaq:ALNY) on Friday reported positive initial Phase 1b clinical trial results for brezosiran, an investigational RNAi therapy for Huntington's disease, demonstrating substantial and sustained reductions in mutant huntingtin protein.

In the highest dose group evaluated, patients achieved mean reductions of 60% to 64% in cerebrospinal fluid mutant huntingtin levels at three months, with individual reductions reaching 83%.

The therapy demonstrated dose-dependent target engagement using two independent assays. Its unique targeting approach reduces both mutant huntingtin and shorter mutant HTT1a.

Safety and tolerability results were encouraging, with follow-up extending to 12 months and no dose-dependent increases in cerebrospinal fluid inflammatory markers, neurofilament light chain or brain ventricular volume.

The findings indicate potential for twice-yearly dosing, which will be further evaluated in an open-label extension study offering eligible participants treatment every six months for up to 36 months.

Alnylam plans to initiate a placebo-controlled pivotal trial in 2027, subject to regulatory alignment, to assess whether brezosiran can slow disease progression in adults with Huntington's disease.