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A new RNAi therapy is showing real promise for Huntington disease. Brezosiran cut levels of the toxic mutant huntingtin protein in spinal fluid by up to 83% in early-stage trial participants, with effects lasting up to 12 months. Developer Alnylam Pharmaceuticals plans to launch a pivotal study in 2027 — a big deal given there are currently zero approved disease-modifying treatments for HD.
A new RNAi therapy is showing real promise for Huntington disease. Brezosiran (ALN-HTT02), developed by Alnylam Pharmaceuticals in collaboration with Regeneron, demonstrated meaningful, dose-dependent reductions in cerebrospinal fluid (CSF) mutant huntingtin (mHTT) levels in an ongoing Phase 1b trial. The findings were unveiled at the 2026 European Huntington's Disease Network Clinical Research Congress in Krakow, Poland.
The drug works by targeting exon 1 of the huntingtin gene's messenger RNA, reducing production of both full-length mutant HTT and the shorter HTT1a protein — a form increasingly linked to disease progression. Encouragingly, the effects appear durable, with some participants showing sustained target engagement up to 12 months post-dose, raising the possibility of a twice-yearly dosing schedule.
By the Numbers:
Why it matters: Huntington disease is a fatal, progressive neurological disorder with no approved disease-modifying therapies. Brezosiran's early efficacy and safety profile — with no dose-dependent increases in inflammatory markers or brain volume changes — make it one of the most compelling candidates in the pipeline. A pivotal trial is planned for 2027.
