A Study to Investigate the Pharmacokinetics and Pharmacodynamics of RO7234292 (RG6042) in CSF and Plasma, and Safety and Tolerability Following Intrathecal Administration in Patients With Huntington's Disease

Inclusion Criteria: * Manifest HD diagnosis * Independence Scale score of \>=70. * Genetically confirmed disease by direct deoxyribonucleic acid testing with a cytosine, adenine, and guanine base sequence found in DNA which is translated into glutamine (CAG) age product (CAP) score \> 400. * Ability to read the words "red," "blue," and "green" in the patient's native language. * Ability to walk unassisted without a cane or walker and move about without a wheelchair on a daily basis as reviewed at screening and baseline visit. * Ability to undergo and tolerate MRI scans. Exclusion Criteria: * 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. * Current active psychosis, confusional state, or violent behavior. * Any serious medical condition or clinically significant laboratory, vital signs, or ECG abnormalities at screening that, in the Investigator's judgment, precludes the patient's safe participation in and completion of the study. * Clinical diagnosis of chronic migraines or history of low pressure headache after lumbar puncture requiring hospitalization or blood patch. * Treatment with investigational therapy within 4 weeks prior to screening or 5 drug elimination half-lives of investigational therapy, whichever is longer. * Concurrent or planned concurrent participation in any interventional clinical study, including explicit pharmacological and non-pharmacological interventions. Observational studies are acceptable. * Unable or unsafe to perform lumbar puncture on the patient. * Previous lumbar surgery that is likely, in the opinion of the Investigator or surgical team, to make IT catheter insertion or IT injection unduly difficult or hazardous. * Poor peripheral venous access. * Scoliosis or spinal deformity making IT injection not feasible in the outpatient setting. * Preexisting intra-axial or extra-axial lesions as assessed by a centrally read MRI scan during the screening period.