Triac Trial II in MCT8 Deficiency Patients

This therapeutic trial will be conducted in patients with MCT8 deficiency (also called Allan-Herndon-Dudley Syndrome (AHDS)), which is due to mutations in monocarboxylate transporter (MCT)8. MCT8 is a thyroid hormone transporter which is crucial for the transport of thyroid hormone from the blood into different tissues. Defective MCT8 results in a lack of thyroid hormone (hypothyroidism) in tissues that are dependent on MCT8 for thyroid hormone uptake, such as the brain. Hypothyroidism in the brain results in severe intellectual and motor disability. Another important feature of this disease is the high serum T3 concentrations in the blood. This results in hyperthyroidism in tissues that are not dependent on MCT8 for their thyroid hormone supply. As a result, patients with MCT8 deficiency have clinical features of thyrotoxicosis such as low body weight, elevated heart rate and reduced muscle mass. Preclinical studies have shown that the T3 analogue tiratricol is transported into cells in an MCT8-independent manner. In animal models mimicking MCT8 deficiency, Triac has been shown to normalize brain development if administrated during early postnatal life. Recently, Triac Trial I (NCT02060474) has shown that tiratricol treatment in patients with MCT8 deficiency improves key clinical and biochemical features caused by the toxic effects of the high T3 concentrations. No drug related serious adverse events have occurred during Triac Trial I. This study will investigate the effect of treatment with tiratricol in young boys (≤30 months) with MCT8 deficiency (also called the Allan-Herndon-Dudley syndrome (AHDS)). The hypothesis tested is that treatment with tiratricol will have a beneficial effect on the hypothyroid state in the brain as well as the hyperthyroid state in peripheral organs and tissues in these patients. Patients will initially be treated for 96 weeks with tiratricol, treatment effect will be evaluated after 96 weeks. After the 96 week treatment period, patients will enter Part II of the trial, evaluating long-term treatment. Patients will be followed for an additional 3 years and treatment effect will be evaluated after 3 years, 4 years and 5 years respectively from start of treatment.