Expanded Access Program for Tiratricol in Patients With Monocarboxylate Transporter 8 Deficiency

Inclusion Criteria:

Each patient must meet all of the following criteria to be eligible:

1. Diagnosis of MCT8 deficiency confirmed with a genetic test.

2. Either tiratricol treatment naïve, or patients who may be on a stable dose oftiratricol having transferred from the Phase 3 MCT8-2021-3 (ReTRIACt) study (NCT05579327) or prior individual investigational new drug (IND).

3. In the Treating Physician's medical opinion, the potential benefits of treatmentwith tiratricol outweigh the potential risks for the patient.

4. Patient or legal representative provided signed and dated informed consent to betreated with tiratricol, through this EAP.

5. Given the severity of the disease, sexual activity in these patients is deemedunlikely. However, where, at the discretion of the Treating Physician sexualactivity is possible for the patient, patients must followprotocol-specified-contraception guidance.

6. Patient is approved for enrolment by the sponsor RTT.

Exclusion Criteria:

Patients who meet any of the following criteria will be excluded from the EAP:

1. Parents, legal representative or, if applicable, patients unwilling or unable tocomply with the Treating Physician's treatment plan related to this EAP for anyreason.

2. Major illness or recent major surgery unrelated to MCT8 deficiency (in the TreatingPhysician's judgement), defined as:

• Conditions requiring repeated hospitalizations that are likely to confoundability to participate in the program.

• Major illness in the 3 months before the screening visit that is likely toconfound the ability of the patient to participate fully within the programand/or confound the assessment of serum total T3 and/or safety.

• Major surgery within the 3 months before the screening visit, or planned totake place during the program, including but not limited to majorabdominal/thoracic/neurosurgical procedures.

• Major/minor abdominal and/or maxillofacial surgery that may inhibit theadministration and/or absorption of tiratricol.

3. Patients with any contra-indication for treatment with tiratricol or any excipientsin the program treatment.

4. Patients using thyroid hormone analogues- such as levothyroxine -or thionamides,such as propylthiouracil. Prior use of these drugs is not an exclusion criterion,provided the use of the medication has subsided and the thyroid hormone levels havestabilized after the cessation of these medications. For patients currently usingthese medications the switch to tiratricol should be made following the above andunder the guidance of an endocrinologist with knowledge of MCT8 deficiency, ifneeded, after consultation with pharmacologist.

5. Known hypersensitivity to tiratricol including any ingredient in the pharmaceuticalformulation.

6. Although very unlikely, as this is a severe X-linked disease: Women who are nursingor pregnant (or women who are planning to become pregnant during treatment withtiratricol).

7. Patients eligible for clinical trials with tiratricol.