Inclusion Criteria:  Subjects must provide a signed and dated informed consent form to participate in the study. Subjects must be able (in the judgment of the Investigator) to understand the nature of the study and all risks involved with participation in the study. Subjects must be willing to cooperate and comply with all protocol restrictions and requirements. Subjects must have successfully completed all Study MT-1186-A02 visits and have been compliant with study drug.  Exclusion Criteria:  Subjects of childbearing potential unwilling to use an acceptable method of contraception from the screening visit until 3 months after the last dose of study medication. Subjects who are sexually active who do not agree to use contraception during the study period. Subjects who are female, of childbearing potential, and pregnant (a positive pregnancy test) or lactating at the screening visit. Subjects who have a significant risk of suicide. Subjects with any suicidal behavior or suicidal ideation of type 4 (active suicidal ideation with some intent to act, without a specific plan) or type 5 (active suicidal ideation with specific plan and intent) based on the Columbia-Suicide Severity Rating Scale (C-SSRS) at Week 48 of Study MT-1186-A02. Subjects who are not eligible to continue in the study, as judged by the Investigator in conjunction with the MTDA medical monitor. Subjects who are unable to take their medications orally or through a PEG/RIG tube.