GENERATION HD2. A Study to Evaluate the Safety, Biomarkers, and Efficacy of Tominersen Compared With Placebo in Participants With Prodromal and Early Manifest Huntington's Disease

Inclusion Criteria

-HD gene expansion mutation carrier status with a cytosine-adenine-guanine-age product (CAP) score of 400-500 inclusive

Either:

• Prodromal HD (defined as Diagnostic Confidence Level (DCL) 2 to 3, Independence Scale (IS) ⩾70, and TFC ⩾8); or

• Early manifest HD (defined as DCL 4, IS ⩾70, and TFC ⩾8);

• Total body weight > 40 kilograms (kg) and a body mass index (BMI) within the range of 18-32 kilograms per meter square (kg/m2)

• Study companion

Exclusion Criteria

• Current or previous use of an antisense oligonucleotide (ASO) (including small interfering ribonucleic acid [RNA]) or any huntingtin gene/protein (HTT) lowering therapy (including tominersen)

• Anti-platelet or anticoagulant therapy within 14 days prior to screening or anticipated use during the study, including, but not limited to, aspirin (unless ≤ 81 milligrams per day [mg/day]), clopidogrel, dipyridamole, warfarin, dabigatran, rivaroxaban, apixaban, and heparin

• History of gene therapy, cell transplantation, or brain surgery

• Hydrocephalus

• Pregnancy or breastfeeding, or intention of becoming pregnant during the study or within 5 months after the final dose of study drug

• History of attempted suicide or suicidal ideation with plan (i.e., active suicidal ideation) that required hospital visit and/or change in level of care within 12 months prior to screening