Developing outcome measures for pediatric mitochondrial disorders: Which complaints and limitations are most burdensome to patients and their parents?

► The FDA stresses the need to include patient key outcome measures in every trial. ► We investigated the complaints and disabilities patients and caretakers experience. ► We observed a very high prevalence of impairment in activities and participation. ► Burdensome symptoms pointed differ between pediatricians, and patients and parents. ► We urge to include a patient representative to the outcome measure selection process.