An adverse event (AE) was any untoward medical occurrence in a participant who received study drug without regard to possibility of causal relationship. A TEAE was defined as an AE that had an onset date or date of worsening on or after the first dose of study drug. A summary of other non-serious AEs and all serious adverse events (SAEs), regardless of causality is located in the 'Reported AE section'.

Least square (LS) mean and 95% confidence interval (CI) were calculated using mixed-model repeated measures (MMRM). The blood tHTT protein value was log-transformed before fitting the MMRM model. The LS means from MMRM model were back-transformed to present geometric mean percent changes.