Kygevvi®, the treatment developed Par UCB for thymidine kinase 2 deficiency (TK2d), was approved Par the FDA on 3 November. An application for marketing authorisation in Europe is currently under review Par the EMA.
On Monday, the Food and Drug Administration (FDA) approved the marketing of Kygevvi®, developed Par UCB, for thymidine kinase 2 deficiency (TK2d). In the United States, this pharmacological treatment, which combines two molecules, doxecitine and doxribtimine, may be prescribed to adults and children whose first symptoms appeared no later than the age of twelve. This is a first for this ultra-rare condition, for which there was previously no treatment.
Lower mortality and improved survival
As indicated Par the FDA, this approval is based on results reported Par the Belgian pharmaceutical company, which combine a phase 2 clinical trial, two retrospective studies and the expanded access programme currently underway in France. A significant difference in mortality was observed between treated patients (4%) and untreated patients (36%), as well as a higher average ten-year survival rate for the former (9.6 years) compared to the latter (5.7 years). Finally, it is emphasised that potential liver dysfunction and gastrointestinal disorders (diarrhoea is very common) must be monitored.
Positive effects on motor milestones and respiratory function
Furthermore, at the Muscular Dystrophy Association (MDA) 2025 conference, UCB presented additional results on the progress of patients treated who had been included in the Phase 2 trial. Three-quarters of them regained one motor milestone they had lost before starting Kygevvi®, and 22.5% regained four or more. Similarly, 16% of patients were able to reduce the amount of time they needed assisted ventilation, and the same percentage were even able to stop using it completely. However, only two out of 19 patients no longer required assistance with feeding.
In Europe, UCB has submitted a marketing authorisation application, which is currently being evaluated Par the European Medicines Agency (EMA).
Thymidine kinase 2, a key enzyme
The TK2 gene, located in the nuclear DNA, codes an enzyme called thymidine kinase 2, which is essential for mitochondrial function. It is involved in the “repair” and synthesis of mitochondrial DNA. When the enzymatic activity of thymidine kinase 2 is insufficient, mitochondria accumulate mitochondrial DNA damages, leading to dysfunction in high-energy-demand tissues, particularly muscles, resulting in muscle impairment affecting motor and respiratory functions, characteristic of TK2 deficiency.