This is a Phase 1-3, multi-center, double-blind, placebo-controlled, multiple-ascending dose (MAD) study in up to 73 patients with AxD. Participants will be randomized in a 2:1 ratio to receive ION373 or matching placebo for a 60-week double-blind treatment period; then all participants will receive ION373 for a 60-week open-label treatment period. Multiple dose cohorts will be evaluated in the study. Cohorts will be enrolled sequentially. The initial participants in each dose cohort must be at least 8 years of age at the time of Screening.~The study will include an optional open-label sub-study in participants <2 years of age at some sites.
The purpose of this study is to evaluate the safety and efficacy of ION373 in improving or stabilizing gross motor function across the full range of affected domains in patients with AxD.