Biopharmaceutical company UCB (EBR:UCB) announced on Monday that it has received approval from the US Food and Drug Administration (FDA) for KYGEVVI for the treatment of adults and paediatric patients living with thymidine kinase 2 deficiency (TK2d), with an age of symptom onset on or before 12 years.

This is the first and only approved treatment for these patients living with TK2d, an ultra-rare, life-threatening, genetic mitochondrial disease characterised by progressive and severe muscle weakness (myopathy) with no approved treatment options beyond supportive care until now.

The approval is supported by safety and efficacy data from one Phase 2 clinical study, two retrospective chart review studies, and an expanded access use programme. The study was conducted with 82 unique patients treated with KYGEVVI or pyrimidine nucleosides with an age of TK2d symptom onset less than 12 years. A regulatory review of doxecitine and doxribtimine is currently underway by the EMA (European Medicines Agency), and further regulatory submissions are planned.

KYGEVVI is not approved for use in any indication by any regulatory authority outside of the United States. The company expects the product to be commercially available in the United States in the first quarter of 2026.