This is a Phase 2 prospective, open-label treatment study of the safety and efficacy of MT1621 in TK2 deficient subjects who participated in the retrospective Study MT-1621-101. Subjects who are being treated with dC/dT and did not participate in MT-1621-101 may also be allowed to enroll with Sponsor approval. For all subjects, it is important to ensure that collection of clinical and functional measurements prior to treatment with dC/dT are sufficient to serve as baseline assessments for purposes of evaluating safety and efficacy.~In MT-1621-102, all subjects will be treated with MT1621 at one of 3 protocol-specified dose levels: 260 mg/kg/day (130 mg/kg/day dC and 130 mg/kg/day dT), 520 mg/kg/day (260 mg/kg/day dC and 260 mg/kg/day dT), or 800 mg/kg/day (400 mg/kg/day dC and 400 mg/kg/day dT), divided in three equal doses (tid). On enrollment into the study, subjects already taking their medication at one of these dose levels will either transition from chemical-grade dC/dT or dCMP/dTMP to the same dose of MT1621, or continue use of MT1621 at their current dose. Subjects who were previously taking chemical-grade dC/dT, dCMP/dTMP, or MT1621 at a dose other than one of these dose levels will be transitioned to a protocol-specified dose of MT1621, whichever is closest to the subjects' previous dose of chemical-grade dC/dT, chemical-grade dCMP/dTMP, or MT1621. The dose may be reduced for tolerability reasons.~Safety and efficacy will be assessed upon enrollment, at 1 month, every 3 months through 18 months, every 6 months through 36 months, then annually thereafter, and at end of study participation. For subjects who did not participate in Study MT-1621-101, specific assessments for each subject will be determined by the Sponsor in discussion with the Investigator based on data collected as baseline assessments for purposes of evaluating safety and efficacy. MT1621 should be administered with food.~The study will evaluate sparse PK sampling at steady state using sparse sampling methodology.
This is a Phase 2 prospective, open-label treatment study of the safety and efficacy of MT1621 in TK2 deficient subjects who participated in the retrospective Study MT-1621-101. Subjects who are being treated with dC/dT and did not participate in MT-1621-101 may also be allowed to enroll with Sponsor approval. For all subjects, it is important to ensure that collection of clinical and functional measurements prior to treatment with dC/dT are sufficient to serve as baseline assessments for purposes of evaluating safety and efficacy.