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.
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
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/1.73m² at Screening