LRRK2-targeting antisense oligonucleotide in Parkinson's disease: a phase 1 randomized controlled trial

# LRRK2-targeting antisense oligonucleotide in Parkinson's disease: a phase 1 randomized controlled trial *Published: 2026 Apr* LRRK2 (encoding leucine-rich repeat kinase 2) variants are the most common genetic cause of Parkinson's disease (PD). Lowering LRRK2 levels and/or inhibiting LRRK2 activity may modify PD-associated neuropathology. BIIB094 (ION859), an antisense oligonucleotide, targets LRRK2 mRNA for degradation. REASON was a first-in-human randomized phase 1 study investigating the safety, tolerability, pharmacokinetics and pharmacodynamics of intrathecal BIIB094 in patients with PD. In part A, 40 participants received single doses of BIIB094 10-150 mg or placebo. In part B, 42 participants, stratified by LRRK2 variant status, received four doses of BIIB094 40-120 mg or placebo every 4 weeks. Adverse events were reported by 64.5% (20/31) of participants in part A and by 84.8% (28/33) of participants in part B. The events were mainly mild to moderate and not dose limiting. No serious adverse events related to BIIB094 were reported in either part A or B. Systemic BIIB094 exposure increased with dose. Cerebrospinal fluid (CSF) LRRK2 and phosphorylated Rab10 levels were lowered by up to 59% and up to 50%, respectively, irrespective of LRRK2 variant status. Concomitant reductions in CSF lysosomal protein levels suggested a potential mechanism whereby LRRK2 therapeutics may impact underlying PD pathophysiology. ClinicalTrials.gov identifier, NCT03976349 ; EudraCT number, 2018-002995-42. DOI: 10.1038/s41591-026-04262-4