30 SEP 2026 — The US Food and Drug Administration has approved Emcitate (tiratricol), the first treatment for MCT8 deficiency, a rare inherited disease in which the brain gets too little thyroid hormone and the rest of the body gets too much. The drug, from Sweden's Egetis Therapeutics, was approved on 28 September.
The approval covers the excess hormone in the blood, not the brain damage that defines the disease.
The broken transporter
MCT8 is a protein that carries thyroid hormone into cells, including across the barrier that protects the brain. In MCT8 deficiency, also called Allan-Herndon-Dudley syndrome, a faulty gene on the X chromosome leaves that transporter broken. It mainly affects boys.
The FDA describes the result as two opposite problems at once. The brain gets too little thyroid hormone, while the hormone builds up in the bloodstream. Many patients cannot walk or sit unaided, have little or no speech and have intellectual disability and feeding difficulties. The excess hormone strains the heart and metabolism. Egetis puts the reported median life expectancy at about 35 years.
How the drug gets around it
Tiratricol is a thyroid hormone receptor agonist that, the FDA says, can enter cells without MCT8. "This drug sidesteps that problem," said Hylton Joffe, a director in the FDA's drug evaluation centre. The effect the FDA cites is a fall in the excess hormone in the blood.
The approval rests on two studies that covered infants to adults: an international, placebo-controlled trial registered as NCT05579327, and a longer open-label study. Across both, treated patients had lower blood thyroid hormone levels and improvements in heart rate and systolic blood pressure, the FDA says.
Emcitate comes as tablets made up into a liquid suspension, taken once a day by mouth or through a feeding tube. The most common side effects were diarrhoea, vomiting, rash and excessive sweating. It should not be combined with other thyroid medication.
What the label does not promise
The label is for "peripheral thyrotoxicosis", meaning the excess hormone outside the brain. Neither the FDA nor Egetis says the drug improves walking, speech or intellectual development. Egetis also notes it is not recommended for ordinary underactive thyroid.
Why treating the body half helps
That still matters to families. The company says the effects of chronic excess hormone on the heart, muscles and other organs are believed to contribute to illness and early death in the disorder. Lowering that load is still a treatment, even if it leaves the brain problem untouched.
What comes next
Egetis expects Emcitate to be on sale in the US in eight to ten weeks, with a specialty pharmacy partner handling supply and a patient support programme. The FDA also gave the company a rare paediatric disease priority review voucher, which speeds a future review. Egetis says it may sell the voucher, possibly in the fourth quarter.
"Until now, patients living with MCT8 deficiency and their families had no FDA-approved treatment option," said Marina Zemskova of the FDA's endocrinology division.
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