In 19 patients who were included in the study because of a possible (low probability) mitochondrial disease, mutations in various non MD-related genes (ADAR, CACNA1A, CDKL5, CLN3, CPS1, DMD, DYSF, GBE1, GFAP, HSD17B4, MECP2, MYBPC3, PEX5, PGAP2, PIGN, PRF1, SBDS, SCN2A) were identified (Table 2; Additional file 1: Table S1). The gene discussed is MECP2; the disease is mitochondrial disease.