The purpose of the study is to evaluate the efficacy of exogenous melatonin in improving sleep quality in HD gene carriers.

Inclusion Criteria:

• Verified HD mutation carriers.
• Patients who report sleep disturbance as measured by a score ≥5 on the Pittsburgh Sleep Quality Index (PSQI);
• Stable concomitant medication (no change of medication during last 30 days prior to inclusion);
• Written informed consent by prospective study participant before conduct of any trial-related procedure;
• Participant must be able to make an informed decision of whether or not to participate in the study.

Exclusion Criteria:

• Pregnant or nursing women;
• Woman of childbearing potential, not using highly effective methods of contraception such as oral, topical or injected contraception, intrauterine device (IUD), contraceptive vaginal ring, or double barrier method such as diaphragm and condom with spermicide) or not surgically sterile (via hysterectomy, ovariectomy or bilateral tubal ligation) or not at least one year post menopausal;
• Presence of any medically not controllable disease (e.g. uncontrolled arterial hypertension or diabetes mellitus);
• Use of benzodiazepines, sedating antidepressants (mirtazapine or trazodone) or sedating antipsychotics (olanzapine and quetiapine) in the previous four weeks;
• Severe cognitive disorders defined as a score < 18 on the MOCA;
• Participation in another investigative drug trial within 2 months;
• Subjects who are unlikely to be compliant and attend scheduled clinic visits as required as determined by the Investigator.