Latest for MCT8 Deficiency
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- FDA decisionFDA approved Emcitate for MCT8 deficiencyFDA
More about MCT8 Deficiency
When MCT8 is missing or broken, the brain cannot take up the hormone it needs to build myelin and wire itself, and every brain scan in the 2020 natural history study showed delayed myelination.
Keep reading about MCT8 Deficiency
The developmental consequences are severe and, so far, permanent: in that study of 151 patients, the motor and cognitive abilities patients had did not improve with age, boys who had not gained head control by 18 months carried a 3.5 times higher risk of death, and 21% had died, most often of pneumonia or sudden death, with a median survival of 35 years.
The second half of the disease is the mirror image of the first. Because the brain is not taking T3 up, the hormone accumulates in the blood, and tissues that do not depend on MCT8, such as muscle, liver, heart and bone, receive far too much of it.
That produces a state doctors call peripheral thyrotoxicosis: 71% of patients in the natural history study were underweight, about a third had a resting heart rate above normal, half had raised blood pressure, and the muscle wasting and sweating families describe come from a body that cannot keep up with its own metabolism.
The blood tests are characteristic and are the fastest route to diagnosis: high T3, low or low-normal T4, and a normal or mildly raised TSH. Genetic testing of SLC16A2 confirms it.
What are the symptoms of MCT8 Deficiency?
These are common symptoms of MCT8 Deficiency, and how strong they are varies from person to person.
- Low muscle tone (hypotonia) from the first months, with poor or absent head control
- Severe delay in motor milestones; most affected boys never sit or walk independently
- Severe intellectual disability with limited or no speech
- Stiffness (spasticity) and abnormal movements (dystonia) that develop over time
- Low body weight and difficulty gaining weight despite adequate feeding
- Resting heart rate that is faster than normal, and heat intolerance or sweating
Who gets MCT8 Deficiency?
MCT8 deficiency is inherited on the X chromosome, so it almost always affects boys, who have only one copy of the gene. Mothers who carry the change usually have no symptoms beyond, in some cases, mild thyroid test abnormalities. Pregnancy and birth are typically uneventful and babies look healthy at first. Poor head control and low tone usually appear in the first 3 to 6 months, but because routine newborn screening measures TSH rather than T3, the diagnosis is often missed for a long time: the median age at diagnosis in the 2020 natural history study was 24 months. Girls are affected only in rare circumstances.
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Which medicines are FDA-approved for MCT8 Deficiency?
There is currently 1 FDA-approved medication for MCT8 Deficiency.
Source: openFDA drug labeling data. This list may not include all treatments. Always consult your doctor.
How to get help paying for MCT8 Deficiency treatment
Charity funds and drugmaker programs for MCT8 Deficiency, checked at the source.
Side effects people have reported to the FDA
Side effects people have reported to the FDA
Real-world side effect reports from the FDA Adverse Event Reporting System (FAERS). Includes both FDA-approved drugs and investigational therapies from active clinical trials. Click any drug to see what patients reported.
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Diagnosis and genetic testing
Genetic testing for MCT8 Deficiency
Genetic testing can confirm a diagnosis, guide treatment decisions, and identify family members who may be at risk.
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Trusted MCT8 Deficiency resources
Reputable organizations and medical references for learning more about MCT8 Deficiency, including disease registries, foundation resources, and clinical guidelines.