How fast does thymidine kinase 2 deficiency (TK2d) progress without intervention? That’s the question explored by the largest dataset to date on untreated pediatric-onset TK2d, and the results reveal a median survival of just 2.6 years from symptom onset. Additionally, more than 80% lost at least one motor milestone, and many experienced escalating care needs, including ventilatory and feeding tube support. Here with Dr. Charles Turck to discuss the findings that highlight the urgent need for earlier diagnosis and intervention is Dr. Cristina Dominguez-Gonzalez, a physician in the Department of Neurology at the University Hospital 12 de Octubre in Madrid.