KYGEVVI[®] (doxecitine and doxribtimine) recommended for approval in the European Union as treatment for Thymidine Kinase 2 Deficiency (TK2d)

Brussels (Belgium) 30 January 2026 – UCB (Euronext Brussels: UCB), a global biopharmaceutical company, today announced that the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) adopted a positive opinion recommending granting marketing authorization under exceptional circumstances for KYGEVVI^® (doxecitine and doxribtimine) for the treatment of pediatric and adult patients with genetically confirmed thymidine kinase 2 deficiency (TK2d) with an age of symptom onset on or before 12 years.¹ The final European Commission (EC) decision is anticipated in Q2 2026.

“This positive CHMP opinion marks a turning point in the treatment of TK2d, offering a new chapter of hope and a meaningful step forward for patients, families, and clinicians alike,” said Donatello Crocetta, Chief Medical Officer at UCB. “We are deeply proud to be one step closer to being able to bring the first and only approved treatment for TK2d to the community.”

"Doxecitine and doxribtimine treatment is a great example of how robust pre-clinical data can be translated into a clinical program in ultra-rare disease, impacting the natural history of a fatal disorder such as thymidine kinase 2 deficiency” said Caterina Garone, Associate Professor of Medical Genetics, University of Bologna, Italy. "The CHMP positive opinion is a significant step toward potential access to the first treatment option for TK2d in Europe.”

Doxecitine and doxribtimine was supported through EMA's PRIority MEdicines (PRIME) scheme, which provides early and enhanced scientific and regulatory support to medicines that have a potential to address patients' unmet medical needs. Marketing authorization under exceptional circumstances may be granted to medicines where the applicant is unable to provide comprehensive data on efficacy and safety under normal conditions of use, because the condition to be treated is rare or because collection of full information is not possible or is unethical. 

About TK2d

TK2d is an ultra-rare, life-threatening, genetic mitochondrial disease characterized by progressive (worsening over time) and severe muscle weakness (myopathy) with no approved treatment options in Europe beyond supportive care.^2,3,4,5 TK2d can impact all parts of a person's daily life and wellbeing and can become worse over time and impact the ability to walk, eat and breathe independently, often necessitating around-the-clock caregiver support.^3,4,6 It is often fatal, with those experiencing initial symptoms on or before the age of 12 years facing a high risk of premature death (often occurring within 3 years after symptom onset).⁷ It is estimated that the worldwide prevalence of TK2d is 1.64 [0.5, 3.1] cases per 1,000,000 people.⁸

Supportive data

Supportive data came from pooled data from two studies* of treatment with doxecitine and doxribtimine in patients with genetically confirmed TK2d with age of symptom onset ≤12 years. These studies investigated the impact of treatment on functional outcomes (i.e. motor milestones, ventilatory support, feeding support) as well as survival.^1,4,9,10 In the studies, the most common side effects associated with treatment were gastrointestinal disorders, including diarrhoea, vomiting, and abdominal pain.¹

About doxecitine and doxribtimine mechanism of action

Doxecitine and doxribtimine are incorporated into the mitochondrial DNA of skeletal muscle, restoring mitochondrial DNA copy number and improving skeletal muscle function in patients with TK2d.¹ 

*These two studies comprise 39 participants with an age of TK2d symptom onset ≤12 years - the median age of TK2d symptom onset was 1.89 years (Q1, Q3 = 1.2, 2.7) and the median duration of treatment was 91.4 months (Q1, Q3 = 80.2, 117.8; all treated > 5 years). Survival was compared to an external control group, after matching on Age of Symptom Onset Category. Information on functional outcomes in the treated patients (motor milestones, ventilatory support, and feeding support) was collected during the pre- and post-treatment period and analysed. 

For more information about the trials visit: https://clinicaltrials.gov/study/NCT03845712 (TK0102/NCT03845712) and https://clinicaltrials.gov/study/NCT03701568 (MT-1621-101/NCT03701568).

For further information, contact UCB:

Global Communications
Nick Francis
T: +44 7769 307745
nick.francis@ucb.com

Corporate Communications, Media Relations
Laurent Schots
T +32.2.559.92.64
laurent.schots@ucb.com

Investor Relations
Antje Witte
T +32.2.559.94.14
antje.witte@ucb.com

About UCB

UCB, Brussels, Belgium (www.ucb.com) is a global biopharmaceutical company focused on the discovery and development of innovative medicines and solutions to transform the lives of people living with severe diseases of the immune system or of the central nervous system. With more than 9 000 people in approximately 40 countries, the company generated revenue of € 6.1 billion in 2024. UCB is listed on Euronext Brussels (symbol: UCB).

Forward-looking statements

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References:

1. EMA/CHMP/384297/2025. January 2026
2. Berardo A, et al. Advances in Thymidine Kinase 2 Deficiency: Clinical Aspects, Translational Progress, and Emerging Therapies. J Neuromuscul Dis. 2022;9(2):225-235.
3. Wang J, et al. eds. GeneReviews^®. [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024.
4. Domínguez-González C, Chiang C, Colson AO, et al. Pyrimidine Nucleos(t)ide Therapy in Patients With Thymidine Kinase 2 Deficiency: A Multicenter Retrospective Chart Review Study. Neurology. 2025;105(6):e213908. doi:10.1212/WNL.0000000000213908.
5. National Institute of Health. TK2-related mitochondrial DNA depletion syndrome, myopathic form. https://medlineplus.gov/genetics/condition/tk2-related-mitochondrial-dna-depletion-syndrome-myopathic-form/#genes. Accessed January 2026.
6. Thymidine kinase 2 deficiency. National Organization for Rare Disorders. Updated September 14, 2022. https://rarediseases.org/rare-diseases/thymidine-kinase-2-deficiency/. Accessed January 2026.
7. Hirano M, et al. The Disease Course of Untreated Patients with Thymidine Kinase 2 Deficiency (TK2d) Aged ≤12 Years at TK2d Symptom Onset: Findings from the Largest International TK2d Dataset. 2025 AAN.
8. Ma Y. 2023 ISPOR Europe. EPH140.
9. ClinicalTrials.gov. NCT03701568. https://clinicaltrials.gov/study/NCT03701568. Accessed January 2026. 
10. ClinicalTrials.gov. NCT03845712. https://clinicaltrials.gov/study/NCT03845712. Accessed January 2026.