Adeno-associated virus gene therapy is emerging as a promising strategy to treat mitochondrial diseases, including thymidine kinase 2 deficiency (TK2d), with studies showing improved survival, restored cellular energy production and better muscle function in preclinical models, according to a review published recently in Molecular Psychiatry.
Mitochondrial diseases such as TK2d are caused by genetic mutations that impair how cells produce energy. In TK2d, the body cannot properly maintain mitochondrial DNA, leading to progressive muscle weakness and organ dysfunction. Gene therapy aims to deliver a healthy copy of the defective gene, helping cells regain the ability to produce energy more effectively.
Adeno-associated viruses, or AAVs, are widely used as delivery tools because they are not known to cause disease and can provide long-lasting gene expression in tissues such as muscle, heart and brain. Researchers can engineer these viruses to carry therapeutic genes directly into affected cells.
In mouse models of mitochondrial disease, including TK2d, AAV-based therapy restored enzyme activity, normalized mitochondrial DNA levels and extended survival. In some cases, combining gene therapy with nucleoside supplements further improved outcomes.
Read more about therapies for TK2d
Importantly for patients, these findings suggest that earlier treatment may lead to better results. Studies show that treating disease before symptoms become severe can prevent or delay damage, while later treatment may still stabilize disease progression. This has direct relevance for TK2d, where early diagnosis and intervention could significantly alter the course of illness.
Despite encouraging progress, several challenges remain. Mitochondrial diseases often affect multiple organs, making it difficult to deliver therapy everywhere it is needed. The small size of AAV vectors limits how much genetic material they can carry, and some patients may have preexisting immunity that reduces treatment effectiveness. In addition, manufacturing these therapies is complex and costly, which may affect access for patients.
“Despite these difficulties AAV-based gene therapy is still the most robust, and overall safe platform to deliver therapeutic genes in different genetic conditions, including mitochondrial diseases,” the review’s authors said.
Researchers are also developing new approaches for mitochondrial diseases caused by mutations in mitochondrial DNA itself, which are harder to treat than nuclear gene defects like TK2d. These include precision gene-editing tools and alternative strategies to express mitochondrial genes from the nucleus, though these methods are still under investigation.
For patients with TK2d, AAV-based gene therapy represents a meaningful step forward. While not yet widely available, ongoing research and clinical trials continue to move the field closer to treatments that could slow or even reverse disease progression, offering new hope for improved quality of life.
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