Thymidine kinase 2 deficiency (TK2d) is a rare mitochondrial disease due to mutations in the TK2 gene (TK2). Deficiency of TK2 enzyme causes depletion and multiple deletions of mitochondrial DNA that lead to progressive muscle weakness that begins in infancy through adulthood. Our studies of a mouse model of TK2d have indicated that deoxynucleosides can be effective in bypassing the enzymatic defect. Ongoing expanded access treatment and clinical trials with deoxynucleosides for TK2d are being conducted internationally.
