Alnylam Pharmaceuticals (Nasdaq: ALNY) presented new clinical data at the European Society of Cardiology Congress 2026, including a prespecified subgroup analysis of the HELIOS-B Phase 3 trial evaluating vutrisiran in patients with transthyretin amyloidosis cardiomyopathy (ATTR-CM).

The analysis, simultaneously published in the Journal of the American College of Cardiology, examined treatment effects in 654 randomized patients, of whom 259 (40%) were receiving tafamidis at baseline. Results showed consistent effects on the primary composite endpoint of all-cause mortality and recurrent cardiovascular events through 33–36 months regardless of baseline tafamidis use. Functional capacity, measured by the Six-Minute Walk Test, was preserved with vutrisiran versus placebo in both groups. The study was not powered to establish benefit specifically in patients receiving background tafamidis.

A post hoc analysis of HELIOS-B found that vutrisiran-treated patients showed 25% less decline in intrinsic capacity score and a 52% reduction in risk of decline compared with placebo. A separate safety analysis showed lower adverse event rates with vutrisiran versus placebo, including 42% fewer gastrointestinal disorder events, 41% fewer nervous system disorder events, and 46% fewer eye disorder events.

A pooled analysis of 1,402 patients across four Phase 3 studies of vutrisiran and patisiran showed consistent treatment effects between female and male patients across both ATTR-CM and hereditary ATTR polyneuropathy.

Alnylam also presented a subgroup analysis from the KARDIA-3 Phase 2 study of zilebesiran, an investigational RNAi therapeutic being co-developed with Roche for uncontrolled hypertension. Among patients receiving a background diuretic with office systolic blood pressure of 140 mmHg or above at baseline, zilebesiran produced greater reductions in mean office and 24-hour ambulatory systolic blood pressure than in the overall study population, including reductions during nighttime hours. Zilebesiran is currently being evaluated in the Phase 3 ZENITH outcomes trial.