Inherited Mitochondrial Disorders

Though inherited mitochondrial disorders (MIDs) are most well known for their syndromic forms, for which widely known acronyms (MELAS, MERRF, NARP, LHON etc.) have been coined, the vast majority of inherited MIDs presents in a non-syndromic form. Since MIDs are most frequently multisystem disorders already at onset or during the disease course, a MID should be suspected if there is a combination of neurological and non-neurological abnormalities. Neurological abnormalities occurring as a part of a MID include stroke-like episodes, epilepsy, migraine-like headache, movement disorders, cerebellar ataxia, visual impairment, encephalopathy, cognitive impairment, dementia, psychosis, hypopituitarism, aneurysms, or peripheral nervous system disease, such as myopathy, neuropathy, or neuronopathy. Non-neurological manifestations concern the ears, the endocrine organs, the heart, the gastrointestinal tract, the kidneys, the bone marrow, and the skin. Whenever there is an unexplained combination of neurological and non-neurological disease in a patient or kindred, a MID should be suspected and appropriate diagnostic measures initiated. Genetic testing should be guided by the phenotype, the biopsy findings, and the biochemical results.