Movement, the act or process of moving, the change of place or position or posture, is a complex process under the control of many different parts of the central nervous system including the brain (frontal cortex, basal ganglia, cerebellum) and spinal cord. As brain involvement is common in all ages of primary mitochondrial disease, many patients with mitochondrial disease encounter movement difficulties, described in medical literature as ‘movement disorders’. Here, we briefly touch upon the movement disorders in children with mitochondrial disease, which have a huge impact on quality of life.
Depending on the spatial distribution or localisation of the brain area affected by mitochondrial disease, a variety of movement disorders have been described, including spasticity, dystonia and ataxia which are either generalised or restricted to a specific part of the body, and are frequently observed in combination with other neurological and non-neurological problems.
In the first description of a child with mitochondrial disease, and what is now known as Leigh syndrome, the affected baby boy had markedly spastic upper and lower limbs. Spasticity or muscle spasm is a frequently observed and progressive movement disorder in Leigh syndrome and other mitochondrial diseases in children. In everyday life, those living with spasticity may experience pain, contractures, pressure sores, decreased functional abilities, and difficulties with mobility. In severe cases, they must rely on caregivers even more than usual, extending the impact spasticity has on their day-to-day lives.
Dystonia is characterised by involuntary muscle spasms and results from abnormal functioning of the basal ganglia. These regions of the brain control the speed and fluidity of movement and prevent unwanted movements. Patients with dystonia may experience uncontrollable twisting, repetitive movements or abnormal postures and positions. These can affect any part of the body, including the arms, legs, trunk, eyelids, and vocal cords. Dystonia can be very painful and debilitating.
Ataxia describes a lack of muscle control or coordination of voluntary movements, such as walking or picking up objects. Ataxia is usually caused by damage to the structure at the back of our brain, the cerebellum. Symptoms include slurred speech, stumbling, falling and incoordination, which have a serious impact on quality of life.
The effect movement disorders have on quality of life in children with primary mitochondrial disease, conditions which are often progressive, is substantial and affects so much of day-to-day living. Patients are not able to properly perform activities of daily living themselves such as self-care, eating and drinking, clothing, writing, typing, and walking, and may become wheelchair bound or need full care for all of their daily needs. Moreover, movement disorders also have an economic aspect, e.g., the financial burden it places on individuals, caregivers and society. Some treatments are available for movement disorders, but these are not always effective, as they do not treat the underlying cause. There remains an urgent need for new treatment options targeting the root cause of mitochondrial disease underlying these burdensome disorders.