About MCT8 deficiency

The monocarboxylate transporter 8 (MCT8) is a protein that facilitates the cellular transport of thyroid hormones T3 and T4. MCT8 is important for the transport of T3 and T4 across the blood-brain-barrier and into different cells in the brain (e.g. neurons). Thyroid hormone is crucial in the development of the brain. If MCT8 is defective, which is the case in MCT8 deficiency (also called the Allan-Herndon-Dudley syndrome; AHDS), the transport of T3 and T4 into the brain is insufficient. This disturbs different developmental processes of the brain, resulting in (severe) intellectual and motor disability. Generalized hypotonia, dystonia and spasticity in the extremities comprise the core neurological symptoms of MCT8 deficiency. Moreover, feeding problems and gastric reflux are common clinical problems.

In addition, the thyroid hormone concentrations in the blood are abnormal, with the concentrations of the active hormone T3 being elevated and the concentrations of the inactive pro-hormone T4 being decreased. The high T3 concentrations in the blood are disadvantageous for the organs that do not rely on MCT8 for their thyroid hormone supply. This results in a hypermetabolic state in the liver, muscle and kidney and an elevated heart rate, collectively leading to a low body weight.

An efficient therapy to cure or prevent MCT8 deficiency is currently lacking, although multiple approaches are currently being investigated.

Although the core symptoms are relatively well-established, many aspects on the clinical picture of MCT8 deficiency are still unknown. Importantly, a good description of the natural development of patients with MCT8 deficiency is lacking and efficient resolutions to problems encountered in daily life are not widely available. Due to its relatively low prevalence and presumed under-diagnosis, most patients live scattered throughout the world and hence knowledge and expertise among health care providers is often isolated.

This registry aims to connect these isolated dots and centralize the available expertise on MCT8 deficiency among parents, doctors and other health care providers (see aims).

For more detailed information about the disease and the mechanism of this disease we refer to http://mct8.info/about-ahds-0.