The participants randomized to this group will receive oral deutetrabenazine for 8 weeks. Week 1: 6 mg once daily; Week 2: 6 mg twice daily (BID); Week 3: 9 mg BID; Week 4: 12 BID; Week 5: 15 mg BID; Week 6: 18 mg BID; Week 7: 21 mg BID; Week 8: 24 mg BID.

The participants randomized to this group will receive oral placebo for 8 weeks. Week 1: 6 mg once daily; Week 2: 6 mg twice daily (BID); Week 3: 9 mg BID; Week 4: 12 BID; Week 5: 15 mg BID; Week 6: 18 mg BID; Week 7: 21 mg BID; Week 8: 24 mg BID.

The participants randomized to this group will receive oral deutetrabenazine for 8 weeks. Week 1: 6 mg tab once daily; Week 2: 6 mg tab (BID); Week 3: 9 mg tab (BID); Week 4: 12 mg tab (BID); Week 5: 15 mg (6 mg tab + 9 mg tab BID); Week 6: 18 mg (9 mg tab + 9 mg tab BID); Week 7: 21 mg (9 mg tab + 12 mg tab BID); Week 8: 24 mg (12 mg tab BID).

The change in swallow function/dysphagia from baseline to maintenance therapy using the clinical swallow assessment Huntington's Disease Dysphagia Scale (HDDS). The Huntington's Disease Dysphagia Scale is an 11-item scale used to monitor swallowing difficulties in persons in early to advanced disease stages. The Huntington's Disease Dysphagia Scale includes questions related to the preparatory oral, oral, pharyngeal, and esophageal phases of swallow. The response options are the following: Question 1-4 and 6-11: 1 No, almost never; 2 Yes, seldom; 3 Yes, sometimes; 4 Yes, frequently; 5 Yes, almost always. Question 5: 1 Yes, almost always; 2 Yes, frequently; 3 Yes, sometimes; 4 Yes, seldom; 5 No, almost never. Higher scores mean a worse outcome.

Non-instrumental assessment and symptoms of dysphagia using the Bedside Swallowing Assessment Scale. The Bedside Swallowing Assessment Scale interpretation: Level 1: irrelevant alterations, scores ≤ 19; level 2: average alterations, scores 20-23; level 3: severe alterations, scores ≥ 24. Higher scores mean a worse outcome.

Assessment of pharyngeal and esophageal dysphagia using the Videofluoroscopic Swallowing Study, also known as the Modified Barium Swallow Study. The instrumental assessment provides a description of any anatomical differences and physiological problems that may be associated with the patients' symptoms in all phases of the swallow. Results from the videoflourographic study are used to rate the severity of dysphagia according to the Dysphagia Outcome and Severity Scale. The Dysphagia Outcome and Severity Scale scores range from 1 to 7, with 7 representing normal swallowing and 1 representing severe dysphagia.

Secondary endpoints are treatment success from baseline to maintenance therapy on body weight. Body weight will be calculated in kilograms.

Treatment success from baseline to maintenance therapy on quality of life of HD patients with dysphagia. The quality of life (specifically Assessment of health status and disability using the World Health Organization Disability Assessment Schedule (WHODAS) version 2.0. The WHODAS 2.0 covers six domains of functioning including cognition, mobility, self-care, getting along, life activities and participation in community activities. The following numbers are assigned to the responses: 0= No difficulty; 1= Mild difficulty; 2= Moderate difficulty; 3= Severe difficulty; and 4= Extreme difficulty or can't do. In this test of global day-to-day functioning, higher scores indicate worse functioning.