MCT8 Deficiency/Allan-Herndon-Dudley Syndrome (AHDS)

MCT8 deficiency (also known as Allan–Herndon–Dudley syndrome) is a rare genetic disorder affecting brain development and thyroid hormone transport. MCT8 deficiency leads to significant lifelong disability, and life expectancy may be reduced due to complications, especially from feeding or respiratory issues.

  • Cause: Caused by mutations in the SLC16A2 gene, which encodes the MCT8 protein—a transporter needed to carry thyroid hormone (T3) into brain cells. It is inherited in an X-linked recessive pattern, primarily affecting males.

  • Features: Severe developmental delay, little or no speech, poor muscle tone (hypotonia) in infancy, spasticity later in life, intellectual disability, and movement problems. Affected individuals often have abnormal thyroid hormone levels (high T3, low T4, normal or slightly elevated TSH).

  • Diagnosis: Based on clinical signs, thyroid hormone testing, brain imaging, and confirmed by genetic testing.

  • Treatment: No cure; treatment focuses on supportive care (physical, occupational, and speech therapy) and managing thyroid hormone imbalance.

Active Trials

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Past Trials

  • Title: Withdrawal of Tiratricol Treatment in Males with Monocarboxylate Transporter 8 Deficiency(MCT8 Deficiency): A Double-blind, Randomized, Placebo-controlled Study

    SPONSOR: Rare Thyroid Therapeutics

    INDICATION: MCT8 Deficiency/ Allan-Herndon-Dudley Syndrome (AHDS)

    PROTOCOL: MCT8-2021-3

    PHASE: 3

    DESCRIPTION: This is a double-blind, randomized phase 3 multicenter placebo-controlled study in at least 16 evaluable male participants diagnosed with MCT8 deficiency. Male participants, from 4 years of age (at randomization) and having demonstrated stable maintenance treatment with tiratricol, will be randomized to receive placebo or tiratricol for 30 days or until reaching rescue criterion (serum total triiodothyronine [T3] > upper limit of normal [ULN] of the participant's normal range, for a sample collected during the 30-day Randomized Treatment Period). The research hypothesis to be tested is that, for participants in the placebo group, removal of tiratricol will lead to an increase of serum total T3 concentration, measured by liquid chromatography with tandem mass spectrometry (LC/MS/MS), above the ULN and requirement of rescue treatment with tiratricol, compared to those who continue to receive tiratricol.

    STATUS: Closed

    RECRUITING PATIENTS: No

    RDR LOCATION: Georgia, Florida, North Carolina