Mitochondrial diseases are, as a group, the most common inherited metabolic disorders and the most frequent inherited disorders at the neurological level.
They are clinically heterogeneous, can occur at any age, and usually can produce a wide range of clinical symptoms, being often considered multisystem diseases. Some mitochondrial diseases can be grouped into specific syndromes, such as Leigh syndrome (infantile subacute necrotizing encephalomyopathy), MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes), or Alpers-Huttenlocher syndrome.
Mitochondrial defects can result from mutations in nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) genes. Regarding genetic suspicion, it is worth mentioning that 80% of adult-onset mitochondrial diseases are due to pathogenic variants in mtDNA; however, they only account for 20-25% of childhood-onset cases, where nuclear genes are more important (Gorman et al., 2014).