Alnylam advances Alzheimer's drug trials, reports mivelsiran safety data

Alnylam Pharmaceuticals (Nasdaq: ALNY) presented updates on its neuroscience pipeline at the Alzheimer's Association International Conference (AAIC) 2026, including new clinical trial initiations and updated safety data for its investigational drug mivelsiran.

The company initiated the APPlauDS Phase 2 study evaluating mivelsiran in people with Down syndrome-associated Alzheimer's disease (DS-AD). The trial will recruit participants with early-stage DS-AD across approximately 30 global sites. Michael S. Rafii, M.D., Ph.D., Professor of Neurology at the Keck School of Medicine of USC, described the study as "the first clinical trial to evaluate whether an RNAi approach can reduce APP overexpression caused by trisomy 21."

Alnylam also reported completion of enrollment in its Phase 2 cAPPricorn-1 study of mivelsiran in cerebral amyloid angiopathy (CAA), a condition defined by progressive amyloid beta deposits in brain blood vessels. Initial results from that trial are expected in 2028, with the primary endpoint being the rate of new lobar microbleeds measured by MRI.

Updated Phase 1 data for mivelsiran in early-onset Alzheimer's disease showed no evidence of increased risk of amyloid-related imaging abnormalities (ARIA). The data, covering up to 30 months of treatment exposure, showed mean maximum reductions of -89.9% in cerebrospinal fluid soluble amyloid beta precursor protein and -70.2% in amyloid beta 42 in the highest dose group. The most common adverse events were procedural pain and procedural headache, with no serious or severe adverse events attributed to the study drug.

Separately, Alnylam shared preclinical data and the design of an ongoing Phase 1 trial of ALN-5288, an investigational RNAi therapeutic targeting tau protein, being developed in collaboration with Regeneron Pharmaceuticals. The Phase 1 trial began in the fourth quarter of 2025.

According to the company, Alnylam and Regeneron together have seven clinical programs targeting neuroscience indications.

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