Leigh's Disease is progressive and starts in infancy between the ages of three months and two years. On rare occasion, Leigh's disease can occur in either adolescents or adults. The disease may be caused by mutations in mitochondrial DNA, or by deficiencies of an enzyme referred to as, 'Pyruvate dehydrogenase.' The symptoms of the disease usually progress at a rapid rate, with the earliest signs potentially being poor sucking ability and a loss of motor skills and head control. The symptoms can also include vomiting, loss of appetite, continuous crying, irritability, and seizure activity. As the disease progresses, the symptoms may include lack of muscle tone, generalized weakness, as well as episodes of lactic acidosis. Lactic acidosis may lead to impairment of the person's kidney and respiratory functioning.
Leigh disease (also called Leigh syndrome and subacute necrotizing encephalomyelopathy) is a rare inherited neurometabolic disorder that affects the central nervous system. The disorder usually becomes apparent in the first year of life, and is characterized by progressive loss of mental and movement abilities (psychomotor regression). A small number of individuals do not develop symptoms until adulthood or have symptoms that worsen more slowly. The first signs of Leigh syndrome seen in infancy are usually vomiting, diarrhea, and difficulty swallowing (dysphagia), which disrupts eating. These problems often result in an inability to grow and gain weight at the expected rate (failure to thrive).
Genetic mutations in the person's mitochondrial DNA associated with Leigh's disease interfere with their energy sources that run cells in areas of their brain and play a role in their motor movements. The main function of mitochondria is the conversion of energy contained in glucose and fatty acids into a substance known as, 'Adenosine triphosphate,' or ATP. The energy within ATP drives the metabolic functioning of cells. Genetic mutations in mitochondrial DNA result in a chronic lack of energy in crucial cells, affecting the person's nervous system and causing a progressive degeneration of their motor functioning.
Another form of Leigh's disease is referred to as, 'X-linked Leigh's disease,' and is the result of mutations in a gene that produces another group of substances which are important for cell metabolism. The gene is only found in a person's X chromosome. Additional names that Leigh's disease is know by include:
Leigh's disease is characterized by degeneration of the person's central nervous system, to include their spinal cord, brain, and optic nerve. The symptoms people with the disease experience are associated with progressive neurological deterioration and can include the loss of motor skills they had previously acquired. The person can experience vomiting, a loss of appetite, irritability, as well as seizures. As Leigh's disease continues to progress, the person can also experience lack of muscle tone, generalized weakness, and episodes of lactic acidosis which may lead to kidney and respiratory impairments.
The symptoms of Leigh disease commonly develop within the first year of the person's life. On rare occasion they may develop later in childhood. Infants with the disease usually develop symptoms that include decreased muscle tone, balance or coordination difficulties, and vomiting. One of the main reasons parents seek medical attention for their child in relation to Leigh's disease is because their child is experiencing a failure to thrive and grow. The child will eventually begin to experience seizure activity as well as lactic acidosis and resulting kidney and respiratory impairments.
Some different eye abnormalities are also associated with Leigh's disease. Paralysis of some or all of the person's muscles of their eye, referred to as, 'Ophthalmoplegia,' is common, in combination with degeneration of their optic nerve, as well as pigmentary retinopathy, a disorder which will eventually lead to blindness.
Due to the cell's inability to produce ATP in person's with Leigh's disease their tissues are not provided with enough energy replenishment and usually perish. Because of this, irreversible damage may happen, first in cells that require more energy such as brain cells. This leads to mental impairments and developmental delays. A number of parts of the person's brain are affected by the lack of ATP and Leigh's disease, to include the person's basal ganglia which assist in regulation of motor performance; their brain stem, which controls functions such as swallowing, breathing, hearing and seeing; and their cerebellum, which controls their ability to balance and their voluntary muscle movements.
There may be a number of different types of genetically determined enzyme defects which may cause Leigh's disease. The majority of people with the disease experience defects of mitochondrial energy production, such as deficiencies of an enzyme of the mitochondrial respiratory chain complex, or the pyruvate dehydrogenase complex. Most of the time, Leigh's disease is inherited as an autosomal recessive trait. Mitochondrial inheritance and X-linked recessive Leigh's disease are exceptions.
A diagnosis of Leigh's disease is generally difficult because of the broad variability in clinical symptoms, as well as the variety of different genetic explanations that cause the disease. Genetic testing for specific nuclear or mitochondrial DNA mutation is something that can be helpful. Laboratory studies can also help in achieving a diagnosis of Leigh's disease. A Muscle biopsy can help to determine if the person is experiencing an abnormality associated with their mitochondria. Because the mitochondria are responsible for the production of energy, if the person is experiencing a deficiency in a protein complex that plays an important function it may be detectable.
With Leigh's disease, the deficiency can be found in one of five complexes which make up the mitochondrial respiratory system. Complex IV, referred to as, 'Cytochrome C oxidase (COX),' is one that people with the disease are commonly deficient in. Unfortunately, while COX deficiency is associated with Leigh disease, it may also indicate other mitochondrial abnormalities. There are mutations found in additional complexes that may cause Leigh's disease.
Medical science has not discovered a treatment that is effective in slowing the progression of Leigh's disease at this time. Doctors commonly administer Thiamine or vitamin B1. Sodium bicarbonate can also be prescribed to help manage lactic acidosis. Researchers are testing dichloroacetate in an attempt to establish its effectiveness in the treatment of lactic acidosis. For people with X-linked Leigh's disease, a high-fat, low-carbohydrate diet is recommended.
Due to the fact that there is no cure for Leigh's disease, as well as the progressive nature of it, maintenance of the person's functioning for as long as possible is the main focus instead of recovery. Physical therapists many times help with exercises that can assist the person to maintain strength and range of motion. As Leigh's disease progresses, an occupational therapist can provide the person with positioning devices for their comfort.