Kygevvi is the first FDA-approved oral therapy for the treatment of Thymidine Kinase 2 Deficiency (TK2d) in adults and pediatric patients with symptom onset at 12 years of age or younger. TK2d is a rare, genetic mitochondrial disorder that leads to progressive muscle weakness and respiratory complications. Kygevvi works by replenishing deoxynucleoside levels to help restore mitochondrial DNA replication and energy production, thereby improving muscle function and slowing disease progression. This approval marks a major advancement in the management of TK2 deficiency, offering patients and families the first targeted treatment option for this debilitating condition.