Thyroid Hormone Analog Therapy in MCT8 Deficiency: Triac Trial Patients
Condition: Allan-Herndon-Dudley Syndrome
Study type: Interventional
Phase: Phase 2

Summary: 
      This therapeutical trial will be conducted in patients with the Allan-Herndon-Dudley Syndrome
      (AHDS), which is mutations in MCT8.

      MCT8 is a thyroid hormone (TH) transporter which is crucial for the transport of TH from the
      blood into different tissues. Dysfunction of MCT8 results in a lack of TH (hypothyroidism) in
      tissues that depend on MCT8 for TH uptake. This local hypothyroidism in the brain of these
      patients causes severe psychomotor retardation.

      In addition, TH serum parameters are highly abnormal in AHDS: high T3, low T4 and normal TSH
      levels. The high serum T3 levels cause local hyperthyroidism in tissues that do not depend on
      MCT8 for cellular transport of TH, resulting in a low body weight and reduced muscle mass.

      Currently, no adequate treatment is available for the AHDS. A T3 analog that does not depend
      on MCT8 for its cellular entry could, at least partially, restore the abnormalities found in
      AHDS. Several in vivo, in vitro and animal studies have shown that the T3 analog Triac is a
      very promising candidate:

        1. Triac binds to the same TH receptors as T3;

        2. Cellular uptake of Triac does not depend on functional MCT8. Hence, in AHDS patients
           Triac will also be available in tissues that require functional MCT8 for TH uptake, e.g.
           the brain;

        3. In vitro studies have shown that neuronal cells differentiate equally well in the
           presence of either Triac or T3;

        4. In Mct8 deficient mice, Triac is taken up by the brain and suppresses serum TSH levels;
           consequently, serum T3 and T4 levels were lowered;

        5. Triac is the treatment of choice in patient with the resistance to thyroid hormone (RTH)
           syndrome. Patient with RTH have high serum TSH and thyroid hormone levels, which shows
           strong similarities to the profile found in AHDS patients; the longstanding experience
           with Triac in RTH indicates its safety and tolerability .

      Thus, Triac treatment could result in normalization of the abnormal serum TH values in AHDS
      patients. Furthermore, Triac could replace the function of T3 in tissues that depend on MCT8
      for TH uptake (e.g. brain).

      The current trial will investigate if Triac treatment in ADHS patients

        1. reduces the toxic effects of the high T3 levels

        2. restores the local TH deficiency in brain.
    

Detailed description: 
      All patients were treated with Triac (Téatrois tablets 350 microgram, Rare Thyroid
      Therapeutics) by individualized dose-escalation, following a pre-defined dose-escalation
      protocol. After the initial dose of Triac (350 microgram) was administered and no predefined
      dose-limiting toxicities were observed, the daily dose was increased progressively in 350
      microgram steps, with a goal of attaining serum total T3 concentrations within the target
      range of 1·4-2·5 nmol per liter. The maintenance Triac dose was continued throughout the rest
      of the study period, but could be further adjusted according to the dose-escalation protocol
      if T3 concentrations were outside the target range during control visits.

      Patients were assessed for study outcomes at baseline and 12 months after starting Triac
      administration. In the interval, patients were evaluated and screened for clinical and
      biochemical signs of hypothyroidism or hyperthyroidism, adverse events were recorded and
      adherence to therapy was assessed. All study procedures were specified in standard operating
      procedures, and were performed by well-trained investigators. Neuropsychological tests were
      conducted according to their manual. All biochemical measurements were performed in a central
      laboratory (Erasmus Medical Centre). To account for any interference of Triac in the
      measurement of serum T3 concentrations, conventional methods were employed to correct for
      cross-reactivity.
    

Intervention name(s): Triac
Intervention type(s): Drug
Intervention description(s): Triac is a naturally occuring T3 metabolite with similar bioactivity and receptor binding profile.
Other intervention name(s): Tiratricol, Téatrois, TA3
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Allan-Herndon-Dudley Syndrome; MCT8; Triac; Therapeutic Trial