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A Study to Evaluate Mivelsiran in Adult Participants With Early-Stage Down Syndrome-Associated Alzheimer's Disease (DS-AD)

A Phase 2, Multicenter, Randomized, Double-blind, Placebo-controlled Study, to Evaluate Efficacy, Safety, Tolerability, and Pharmacodynamics of Intrathecally Administered Mivelsiran in Adult Participants With Early-Stage Down Syndrome-Associated Alzheimer's Disease (DS-AD)

Who can join

Ages 40 to 55 · All sexes

Inclusion Criteria:

* Clinical diagnosis of Down-Syndrome (DS) associated with trisomy 21
* Positive amyloid PET scan
* Cognitively stable in the opinion of the investigator
* Seizures must be well controlled with no occurrence of seizures in the 6 months prior to screening

Exclusion Criteria:

* Has severe intellectual disability (ID)
* Has a history of DS regression disorder
* Has alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \>2×upper limit of normal (ULN) at Screening
* Has estimated glomerular filtration rate (eGFR) \<45 mL/min/1.73m\^2 at Screening
* Has recently received an investigational agent
* Has had treatment with amyloid-targeting antibody
* Comorbidities such as obstructive sleep apnea and hypothyroidism that are not well controlled

Note: other protocol defined inclusion / exclusion criteria apply

About the study

The purpose of the study is to evaluate the effect of mivelsiran in adult participants with early-stage DS-AD and to characterize the safety, tolerability, and pharmacodynamics (PD) of mivelsiran. The study will be conducted over 2 periods: a 24-month double-blind period and an optional 12-month open-label treatment extension (OLE) period. The estimated duration of study participation, inclusive of screening, treatment, and additional safety follow-up, is up to 39 months.

What is being tested

• Mivelsiran (drug)
• Placebo (drug)

Sponsor: Alnylam Pharmaceuticals · Participants: 58 · Started: Aug 17, 2026

Contact the study team

• Alnylam Clinical Trial Information Line · Phone: 1-877-ALNYLAM
• Alnylam Clinical Trial Information Line · Phone: 1-877-256-9526

Official record on ClinicalTrials.gov — NCT07636811

Locations in the U.S.

Conditions

• Down Syndrome

From ClinicalTrials.gov, data retrieved Nov 15, 2026. Each study sets its own eligibility; the study team decides who can join.