TK2 deficiency myopathy: towards a first treatment in Europe and improved disease monitoring
Patient care and research in mitochondrial myopathies caused by thymidine kinase 2 (TK2) deficiency are currently advancing on several fronts, with the possible arrival of a first therapy in Europe for early-onset forms and improved monitoring of disease progression in late-onset forms.
Mitochondrial myopathy with TK2 deficiency is a rare genetic disease that deprives muscles of the energy required for normal function and leads to progressive muscle weakness.
Patients in Europe currently have no approved disease-specific treatment, and management is limited to supportive care such as physiotherapy and respiratory support.
Towards a first therapy in Europe
In January, the European Medicines Agency (EMA) issued a positive opinion regarding the marketing authorisation of a first treatment, Kygevvi (doxecitine and doxribtimine), already approved in the United States.
In one study, 84% of patients regained at least one motor ability after receiving this treatment. Another analysis also showed improvements in respiratory function and a reduced risk of death after approximately two years of treatment.
The EMA opinion is now under review by the European Commission, which will make the final decision regarding marketing authorisation across the European Union.
The EMA recommendation applies only to patients whose symptoms began before the age of 12 years, as data on the impact of this treatment remain limited in patients with later-onset disease.
Better understanding the progression of late-onset forms
A Spanish study followed 11 patients over two years, whose first symptoms appeared at around 27 years of age, in order to better understand the progression of late-onset forms and optimise treatment strategies.
Progressive muscle weakness affects mobility as well as respiratory function, with more than 70% of participants requiring ventilatory support. Disease progression was not identical in all individuals, with greater motor and respiratory decline observed in patients whose symptoms began during adolescence or early adulthood.
Researchers also identified tools to measure disease progression that could be used to assess the efficacy of future treatments. This is notably the case for the blood biomarker GDF15, whose elevated levels were associated with loss of respiratory and motor function.
These advances could not only improve current management of early-onset forms but also pave the way for future clinical trials in late-onset disease.
Sources
First treatment for rare thymidine kinase 2 deficiency.
European Medicines Agency (EMA). Press release, 30 January 2026.
Exploring Outcome Measures for Mitochondrial Myopathies; Insights From a Longitudinal Study on TK2 Deficiency.
Martin-Jimenez P, Bermejo-Guerrero L, Ochoa LE et al.
J Inherit Metab Dis. 2026 Jan.