28-Day Study of SAGE-718 on Functioning Capacity in Participants With Huntington's Disease

A 28-Day Randomized, Placebo-Controlled, Double-Blind, Parallel Groups and Normative Comparison Study to Evaluate the Effect of SAGE-718 on Functioning Capacity in Participants With Huntington's Disease

The primary purpose of this study is to assess the magnitude of the baseline difference between participants with early Huntington's Disease (HD) and healthy participants (HP) with respect to measures of cognitive performance.

Inclusion Criteria:

For all

1. Agree to refrain from drugs of abuse for the duration of the study and from alcohol during the 48 hours preceding each study visit.

   Additional criteria for participants with HD only:

2. Be ambulatory, able to travel to the study center, and, judged by the investigator, is likely to be able to continue to travel to the study center to complete study visits for the duration of the study.

3. Have:

   1. Genetically confirmed disease with cytosine, adenine, and guanine (CAG) expansion ≥36.
   2. At screening, Unified Huntington's Disease Rating Scale (UHDRS) Total Functional Capacity (TFC) >6 and <13, suggesting no more than a moderate level of functional impairment.
   3. No features of juvenile HD.

4. CAG-Age-Product (CAP) score >70, as calculated using the CAP formula: Age × (CAG - 30) / 6.49.

5. Score of 15 to 25 (inclusive) on the Montreal Cognitive Assessment (MoCA) at screening, indicating the presence of cognitive impairment.

Additional criteria for HP only:

1. Score ≥26 on the MoCA at screening.
2. Have no known family history of HD; or, have known family history of HD but have genetic test results available that show a normal CAG repeat length for both Huntingtin (HTT) alleles (<36).

Exclusion Criteria:

For All

1. Receive any prohibited medications within 30 days of Screening and during participation in the study
2. Have participated in a previous clinical study of SAGE-718, have previous exposure to gene therapy; or have participated in any HD investigational drug, biologic, or device trial within 180 days, or a non-HD drug, biologic, or device trial within 30 days or 5 half-lives (whichever is longer). (Note: participants with confirmation of enrolment in the placebo arm of these trials would not be excluded.)
3. Is known to be allergic to any of SAGE-718 excipients, including soy lecithin.

Additional criteria for participants with HD only:

1. Had gastric bypass surgery, has a gastric sleeve or lap band, or has had any related procedures that interfere with gastrointestinal transit.
2. Receive any prohibited medications within 30 days of Screening and during participation in the study.