The first and only approved treatment for adults and children with thymidine kinase 2 deficiency (TK2d), an extremely rare and potentially fatal genetic mitochondrial disease, is KYGEVVI® (doxecitine and doxribtimine), which was approved by the U.S. Food and Drug Administration (FDA).
The medication, created by the multinational biopharmaceutical corporation UCB, is only authorized for use by adults and children whose symptoms started at or before the age of 12.
A Pivotal Breakthrough for a Devastating Disease
A rare mitochondrial depletion syndrome called TK2d is characterised by progressive and severe muscle weakness (myopathy), which frequently makes it difficult to walk, breathe, and swallow. The disorder is brought on by a genetic flaw that hinders the body’s capacity to create and fix mitochondrial DNA. The illness frequently results in death, especially in those with early onset symptoms who are at a high risk of dying young, frequently within three years. It is estimated that there are 1.64 cases of TK2d for every million people worldwide.
By bypassing the defective TK2 enzyme and promoting mitochondrial DNA replication, KYGEVVI, a combination of two pyrimidine nucleosides, aims to treat the underlying cause of the illness.
The approval of doxecitine and doxribtimine represents a pivotal moment for the TK2d community who previously had no FDA-approved treatment options for this rare genetic mitochondrial disease beyond supportive [palliative] care,
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Significant Survival and Functional Benefit
Data from a Phase 2 clinical study, two retrospective chart reviews, and an expanded access program that showed notable improvements in patient outcomes served as the foundation for the FDA’s approval.
- Survival Rate: A comparison of 78 matched pairs of patients who received treatment and those who did not revealed a significant improvement in survival. Compared to 28 deaths (36%) in the external control group, there were only three deaths (4%) in the KYGEVVI group. The overall risk of death was lowered by about 86% as a result of treatment.
- Long-Term Survival: At ten years, the treated patients’ mean survival time was 9.6 years, while the control group’s was 5.7 years.
- Motor Function: 75% of patients with early-onset disease were able to regain at least one motor milestone that had been lost, giving them new hope for a higher quality of life and greater independence in their daily lives.
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KYGEVVI’s critical importance to the patient community was highlighted by its multiple FDA designations, which included Orphan Drug, Breakthrough, Priority Review, and Rare Paediatric Disease designations. According to UCB, the medication should be on the market in the United States by the first quarter of 2026.
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