POLG2 and mitochondrial disease: One single screening study investigating 112 POLG-negative unrelated individuals with possible early-onset mitochondrial disease identified eleven childhood-onset cases with heterozygous POLG2 mutations [14], of which three individuals (age at examination 5.7 ± 4.0 years, 1 female) had variants scored at least possibly pathogenic according to the criteria applied in our study.