A Randomised Controlled Trial, Of N-Acetyl Cysteine (NAC), for Premanifest Huntingtin Gene Expansion Carriers

Who May Qualify: - Able to provide willing to sign a consent form - Huntingtin gene expansion carrier with \>= 39 CAG repeats - Absence of unequivocal motor signs of HD - that is, UHDRS - Diagnostic Confidence Level needs to be \<4 upon enrolment - Expected to develop clinical HD within 10 years of trial enrolment using the Langbehn formula - Availability of an informant for corroborative history - Negative serum pregnancy test for women of childbearing potential - If of childbearing potential, is able and agrees to remain abstinent or use adequate contraceptive methods - Ability to tolerate MRI scans - Ability to tolerate blood draws - Able to comply with all study protocol requirements, according to the investigators judgement - In the opinion of the investigator, medically, psychiatrically and neurologically stable at the time of enrolment Who Should NOT Join This Trial: - Diagnosis of clinical HD - Known hypersensitivity to NAC - Pregnancy, breastfeeding or intention to do so prior to the end of the study - Exposure to any investigational drugs within 30 days of Baseline Visit - Use of supplemental NAC - Abnormalities in laboratory measurements, ECG or vital signs at screening, which precludes safe participation in the study - Current or history of substance abuse within one year of Baseline visit - Unstable psychiatric or acute medical illness including cancer, as determined by investigator - Current use of antipsychotic medications or Tetrabenazine - History of gene therapy, cell transplantation, or any experimental brain surgery - History of attempted suicide or suicidal ideation within 12 months prior to screening - Pre-existing structural brain lesion as assessed by a centrally read MRI scan during the screening period Always talk to your doctor about whether this trial is right for you.