A recent study published in the Journal of Neuromuscular Diseases found that early treatment of infantile-onset thymidine kinase 2 deficiency (TK2d) with doxecitine and doxribtimine not only halts but may also reverse disease progression.
During treatment, all patients regained at least two previously lost milestones. Furthermore, those requiring feeding support and invasive ventilation before treatment successfully discontinued support.
The study included four infants who received oral doxecitine and doxribtimine under a special early access program in Turkey. Participants began treatment between 19 and 24 months of age, with treatment duration ranging from four to 81 months.
At baseline, all four participants exhibited low muscle tone and had lost at least one motor milestone. All patients experienced difficulty feeding, with three also developing respiratory difficulties.
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After treatment initiation, three patients gained the ability to walk on their own. The fourth individual, who had received treatment for four months at the time of publication, had just begun walking without assistance.
All participants were also able to stand unassisted, sit independently and control their heads after receiving doxecitine and doxribtimine. None lost milestones while on treatment.
Moreover, reversal of milestone loss occurred rapidly in some cases, with patients gaining or regaining motor skills within a few weeks or months of beginning therapy.
By the time of the last visit, levels of serum creatinine kinase and lactate had decreased as well. No participants discontinued treatment or required dose adjustments.
Limitations of the study include the small sample size and lack of a control group. Nonetheless, these results underscore the potential of doxecitine and doxribtimine for this patient population.
“Our findings provide further evidence that early initiation of pyrimidine nucleoside therapy can dramatically alter the natural course of infantile-onset TK2 deficiency, the most severe form of the disease,” the authors concluded.
The U.S. Food and Drug Administration approved doxecitine and doxribtimine for adults and children with TK2d in November 2025. The European Commission approved the drug in March 2026.
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