Comparison Between [11C]UCB-J and [18F]SynVest-1 PET in HD.

Inclusion Criteria: 1. Healthy controls (n = 10-20) * Subject is judged to be in good health by the investigator on the basis of medical history, physical examination including vital signs, clinical laboratory test and urinalysis. * No history or evidence of current major neurological, internal or psychiatric disorder, based on the medical assessment as described hereabove and neuropsychological assessment. * In subjects \< 60 years of age, an unremarkable structural MRI scan as assessed by expert radiologist. In subjects \>= 60 years of age white matter hyperintensities corresponding to a white matter lesion (WML) Fazekas score \< 2 on the Age-Related White Matter changes scale are acceptable. 2. HD-ISS stage 3 HD mutation carriers (n = 10) * HTT CAG repeat expansion 40 - 50 * stage 3 as determined by the HD-ISS staging criteria * UHDRS TFC \>/= 10 3. HD-ISS stage 2 HD mutation carriers (n = 10) * HTT CAG repeat expansion 40 - 50 * stage 2 as determined by the HD-ISS staging criteria * PIN score 0.47 - 1.84 Exclusion Criteria: * Neuropsychiatric diseases; for HD mutation carriers any neuropsychiatric diseases other than HD * Major internal medical diseases * White matter lesion load on FLAIR Fazekas score 2 or higher or other relevant MRI abnormalities * History of alcohol abuse or current alcohol abuse (chronic use of more than 15 units per week) or drug use * Contraindications for MR * Subject suffers from claustrophobia or cannot tolerate confinement during PET-MRI scanning procedures; subject cannot lie still for 30 minutes inside the scanner. * Subject is unwilling to avoid unusual, unaccustomed, or strenuous physical activity (i.e., weightlifting, running, bicycling) from the time of the pre-study visit until the end of scanning. * Subject does not understand the study procedures or does not have a guardian who understands the study procedures. * Subject (or guardian) is unwilling or unable to perform all of the study procedures or is considered unsuitable in any way by the principal investigator. * Subject is on anticoagulant therapy. * Subject is pregnant (according to Ulti Med hCG urine test) or breastfeeding. * Subject is a woman of childbearing potential who does not agree to apply appropriate contraception methods during study participation and continues to do so for at least 6 months after study completion. * Subject is a man with a pregnant or non-pregnant WOCBP partner, who does not agree to use a condom and continue to do so until 90 days after study completion. In addition, the non-pregnant WOCBP partner should use a highly effective method of contraception.