FDA Approves First Drug for Thymidine Kinase 2 Deficiency
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by Kerri Miller
November 4, 2025
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2 min
7 Key Takeaways
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1
Kygevvi is the first treatment approved for TK2d.
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2
TK2d symptoms onset at age 12 or younger.
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3
Recognized as an ultra-rare mitochondrial disease.
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4
FDA granted Breakthrough Therapy Designation to Kygevvi.
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5
Efficacy based on phase 2 trial data and retrospective studies.
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6
Treated patients showed better survival compared to untreated.
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7
Common side effects include gastrointestinal issues and elevated liver enzymes.
Kygevvi (doxecitine and doxribtimine) has received FDA approval as the first treatment for thymidine kinase 2 deficiency (TK2d), a rare mitochondrial disease with symptom onset before age 12. This inherited disorder leads to impaired mitochondrial DNA production, resulting in severe clinical symptoms like muscle weakness and respiratory failure. The approval follows promising clinical trial data, which show significantly improved survival rates among treated patients compared to those who received no treatment. Common adverse effects include gastrointestinal issues and liver enzyme elevations.
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