Building the Evidence Behind the First Approved Treatment for TK2 Deficiency

The approval of doxecitine and doxribtimine marked the culmination of decades of research into thymidine kinase 2 deficiency (TK2d), an ultra-rare mitochondrial myopathy that previously had no approved disease-modifying treatment. What began as laboratory work investigating the biology of mitochondrial DNA maintenance ultimately evolved into the first approved therapy for patients with this progressive and often fatal disorder.

In this NeurologyLive® Special Report, Michio Hirano, MD, professor of neurology at Columbia University Irving Medical Center and a lead author of the pivotal Brain Communications publication supporting the therapy, examines the scientific discoveries, clinical development, and integrated efficacy and safety data that reshaped the treatment landscape for TK2 deficiency. Throughout the series, he provides clinical perspective on how these findings translate into patient care.

This episode focuses on the path that led to the therapy's FDA approval in November 2025 and subsequent European approval in March 2026. Hirano recounts the progression from preclinical studies in a severe mouse model to compassionate use programs and ultimately a multicenter phase 2 trial, highlighting the key findings that demonstrated meaningful improvements in survival and motor function and established the foundation for regulatory approval.