FDA clears first drug for MCT8 deficiency

Sweden's Egetis Therapeutics has won approval in the US for the first-ever treatment for people living with the ultra-rare genetic disease MCT8 deficiency.

MCT8 deficiency, also known as Allan-Herndon-Dudley syndrome, is an X-linked genetic disorder that impairs the MCT8 transporter system that ushers thyroid hormones into the central nervous system. This results in low levels in the brain, slowing brain metabolism and impairing neurological function, while simultaneously overloading the rest of the body with excess levels of the hormone.

Egetis' Emcitate (tiratricol), a thyroid hormone receptor agonist, has been cleared by the FDA to treat peripheral thyrotoxicosis in adult and paediatric patients with MCT8 deficiency, which the FDA said is a "devastating" disease in need of "meaningful treatment options."

Symptoms of MCT8 deficiency include an inability to walk or sit independently, absent or severely limited speech, intellectual disability, feeding difficulties, and chronic stress on the heart and metabolism, according to the regulator. The typical life expectancy for patients is around 35 years.

Hylton Joffe, director of the Office of Cardiology, Haematology, Endocrinology, and Nephrology at the FDA's Centre for Drug Evaluation and Research (CDER), explained that Emcitate "can enter cells on its own without relying on the broken transporter, leading to a decrease in the elevated blood thyroid hormone levels."

Egetis' drug, given as a once-daily liquid suspension by mouth or feeding tube, was shown in clinical trials to reduce excess levels of thyroid hormone in the blood and improve some other peripheral symptoms of the disorder, such as elevated systolic blood pressure and heart rate.

Epidemiological estimates suggest that MCT8 deficiency has a prevalence of 1 in 70,000 male individuals, which means it would affect between 5,000 and 10,000 boys and men in the US and Europe combined.

"Today marks a turning point for patients living with MCT8 deficiency and their caregivers, who have waited long for an approved treatment in the US," said Nicklas Westerholm, chief executive of Egetis.

"Our immediate focus is ensuring that eligible patients can access Emcitate as quickly as possible," he added. The drug was approved in the EU in December 2025, and made SEK 17 million (around $1.7 million) in the second quarter of this year after an initial launch in Germany in May.

The FDA approval has also earned Egetis a rare paediatric disease Priority Review Voucher (PRV), which can be used to shorten a drug review and can be worth $100 million to $200 million if sold on to another drug developer. The Stockholm-based company said it is exploring a possible sale of the PRV, which would take place before the end of the year.

Pricing in the US has not been revealed – more details may be forthcoming on a company conference call later today – but in Germany the list price is around €10,000 per month for a month's supply of 60 tablets, before discounts.

Other drugs being developed for MCT8 deficiency include Arizona-based PriZm Therapeutics' synthetic thyroid hormone analogue, SRW101, which crosses the blood-brain barrier and could provide an option to address the CNS consequences of the disorder.

Meanwhile, Egetis has started developing Emcitate for a follow-up indication, resistance to thyroid hormone beta (RTH beta), which affects about 1 in 40,000 people and leads to reduced sensitivity to thyroid hormones.

Image by Steve Buissinne from Pixabay