There is currently no specific age range specified for using Exondys 51, but a two-part Phase 3 study scheduled to run until 2026 has recruited boys and young men aged 4 though 21 who meet the study criteria. Previous studies have only investigated boys up to age 19 years. Symptoms of Duchenne muscular dystrophy (DMD) usually appear between 3 and 5 years of age and the condition primarily affects boys at a rate of about 1 in every 3,600 male infants born. If you have an older child, the best thing you can do is talk to your doctor about Exondys 51 treatment.