Mitochondrial diseases are a series of often hereditary disorders characterized by dysfunction of the mitochondria, organelles that are present in all cells. Mitochondria have their own genome and play a vital role in cell function, producing energy via the process of cellular respiration.
Mitochondrial diseases are caused by genetic mutations that affect this energy production. Elucidating the causes of mitochondrial diseases is particularly complex because the functionality of mitochondria does not just depend on the mitochondrial genome; the mitochondrial genome is also associated with the cell genome (known as the nuclear genome as it is contained in the nucleus). This means that mitochondrial diseases can be caused by mutations in either the mitochondrial or the nuclear genome.
Clinical diagnosis of mitochondrial diseases is complicated, and individuals often develop extremely variable symptoms involving different organs or tissues. But most typically, mitochondrial diseases are caused by mitochondrial dysfunction in tissues that require a high energy supply, namely the heart, the brain and the muscles.
Depending on the number of mitochondria and organs affected, mitochondrial diseases can take very different forms, ranging from conditions only affecting the eyes, like Leber's hereditary optic neuropathy (LHON), to multisystem disorders characterized by severe neurological problems, such as Alpers syndrome. Many mitochondrial disorders are characterized by neurological or muscular symptoms.
Given the wide-ranging nature of possible symptoms, patients can initially be treated by doctors specializing in many different fields, including neurologists, intensive care specialists, pediatricians, geneticists, endocrinologists, diabetologists, nephrologists, cardiologists, hepato-gastroenterologists, ophthalmologists and ENT specialists.
Mitochondrial diseases can occur at any age (in newborns, infants, children, adolescents and adults). They develop very differently depending on the form of the disorder and the individual. Given their high level of variability, it is not always possible to establish a precise prognosis, but the outlook is generally poor and the condition may be life-threatening, especially in early-onset forms.
Mitochondrial diseases are thought to be the most common form of metabolic disorder, with one case in every 5,000 births. In France, it is thought that there are 200 new cases each year, but the actual figure is probably higher because of the difficulties associated with diagnosis.
There are no treatments available to cure mitochondrial diseases, but symptomatic treatments can slow their development. These can include taking food supplements and lifestyle changes such as rest and physical exercise. Early diagnosis of patients with mitochondrial diseases is crucial so that treatment can start as soon as possible.