MCT8-specific thyroid hormone cell transporter deficiency

What is MCT8-specific thyroid hormone cell transporter (THCT) deficiency?

MCT8-specific thyroid hormone cell transporter (THCT) deficiency is a rare genetic condition. Common findings in these children include: developmental delay, poor head control, low muscle tone, and unclear or no speech. Not everyone with this disorder has all of the findings or is affected to the same degree. Generally males with this condition also have a thyroid hormone problem that is less severe in their mothers.

The thyroid gland: The thyroid gland is a small gland at the base of the neck. It weighs only about 25 grams. However, the hormones it secretes are essential to all growth and metabolism. The gland is a regulator of all body functions.

What causes MCT8-specific THCT deficiency?

MCT8-specific THCT deficiency is caused by a change (mutation) in the MCT8 (Monocarboxylate transporter 8) gene. Females have two copies of the MCT8 gene, and males have one copy.

Genes: are instructions to make proteins.

Proteins: are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies; which are necessary to the functioning of an organism. They are essential in our diet for the growth and repair of tissue.

When there is a change in the instructions, the protein may not be made or work properly. If a male has a change in his only copy of the MCT8 gene, he will not be able to make the normal protein and develop the findings of MCT8-specific THCT deficiency. Females with a change in one copy of the MCT8 gene will also have a normal copy of the gene. Thus, they will not have any signs of the disorder, but will have a 50% chance of passing it on to their sons.

Resources

Testing for MCT8-specific Thyroid Hormone Cell Transporter Deficiency - Information for Patients and Families (PDF)