Mitochondria produce cellular energy, which is of vital importance for cellular metabolism. The organelles contain their own genetic material (i.e. mitochondrial DNA (mtDNA)) with a matrilineal inheritance. Mutations in the mtDNA may cause mitochondrial disease affecting multiple organs leading to diabetes, hearing impairment, muscle fatigue, ptosis and stroke-like episodes in varying combinations and severity. The variable phenotypic presentations make it a challenge to recognize mitochondrial diseases and, consequently, the correct diagnosis is often delayed.