UCB has announced that the U.S. Food and Drug Administration (FDA) has approved Kygevvi (doxecitine and doxribtimine) for the treatment of genetic mitochondrial disease, thymidine kinase 2 deficiency (TK2d), in both adults and children who begin exhibiting symptoms before the age of 12.

TK2 deficiency is a rare and progressive mitochondrial disorder that leads to severe muscle weakness, known as myopathy. The approval of Kygevvi marks a significant advancement for patients affected by this devastating disease, who previously had no FDA-approved treatment options beyond supportive or palliative care.

The FDA’s decision was supported by data from a Phase II clinical trial, two retrospective chart review studies, and an expanded access program, all of which demonstrated the therapy’s efficacy and safety.

Kygevvi combines two pyrimidine nucleosides, doxecitine and doxribtimine, which act by integrating deoxycytidine and deoxythymidine into skeletal muscle mitochondrial DNA. This mechanism helps restore mitochondrial DNA copy numbers that are compromised by TK2d mutations, as demonstrated in preclinical studies.

Dr. Donatello Crocetta, UCB’s Chief Medical Officer, stated: “The approval of doxecitine and doxribtimine represents a pivotal moment for the TK2d community, who have long awaited a dedicated therapy. We extend our deepest gratitude to the patients, families, advocates, healthcare providers, and clinical research teams who made this milestone possible.”

Kygevvi has received multiple FDA designations, including rare pediatric disease, breakthrough therapy, priority review, and orphan drug status. Additionally, UCB has been granted a rare pediatric disease priority review voucher (RPDPRV), which may be used for a future product application.

Currently, Kygevvi is approved only in the United States, with commercial availability expected in the first quarter of 2026.

This latest approval follows UCB’s 2024 FDA approval of Bimzelx (bimekizumab-bkzx) for the treatment of three inflammatory conditions in adults, further reinforcing the company’s commitment to advancing innovative therapies for complex diseases.