Leigh's Disease (Leigh's Syndrome)
The prognosis of Leigh disorder is very poor, with patients mostly living up to six to seven years after diagnosis. Although some patients may live until mid-teenage years.

Leigh syndrome is a rare inherited genetic disorder that affects the central nervous system. The prognosis of Leigh disorder is very poor, and patients with it mostly live up to six to seven years, but some may live until mid-teenage.

Leigh syndrome is a progressive neurometabolic disorder where the symptoms may be observed in infants who are about three months to two years of age and often after any viral infection in children who appear normal at birth. Symptoms rarely manifest in teenagers and adults because they worsen slowly.

What causes Leigh syndrome?

Leigh syndrome is inherited and may be caused by mutations in more than 75 genes. The location of the gene determines the inheritance of this syndrome. The mutated gene responsible for Leigh syndrome may be present in the mitochondrial or nuclear DNA.

Mitochondrial DNA

  • Mitochondrial DNA–associated Leigh syndrome follows a mitochondrial inheritance pattern, also called maternal inheritance (from mother), because only the egg cells pass the mitochondria to offspring.
  • Both men and women in all generations of a family can be affected.
  • However, men cannot pass this condition to their children.
  • Mothers of children with Leigh syndrome may be affected but may not have the symptoms.
  • Mitochondrial DNA mutations cause almost 20 percent of cases.
  • Mitochondrial mutations may occur in normal individuals who don’t carry the gene, and this condition is called de novo mutation.

Nuclear DNA

  • Nuclear gene-encoded Leigh syndrome may be inherited in autosomal recessive or X-linked recessive.
  • Because men contain one X chromosome, X-linked recessive conditions occur in men.
  • Women have two sets of X chromosomes, so X-linked recessive conditions may be present in women, but they are usually unaffected because there is a copy of a healthy X chromosome.
  • However, some women may be affected, but it is very rare.
  • Most of the cases of Leigh syndrome are associated with nuclear DNA mutations.

Several mutations affect numerous mitochondrial pathways that account for major variations in how the disease manifests and progresses. High lactate levels in the cerebrospinal fluid may potentially be a risk factor for poor prognosis because it indicates significant metabolic stresses caused by insufficient oxidative phosphorylation.

What are the symptoms of Leigh syndrome?

The earliest indications of Leigh syndrome in children are typically vomiting, diarrhea, and trouble swallowing (dysphagia), which interfere with feeding, frequently leading to an inability to grow and acquire weight at the desired rate (failure to thrive).

Leigh syndrome is characterized by severe muscular and mobility difficulties. Individuals with this syndrome may have low muscle tone (hypotonia), involuntary muscular spasms (dystonia), and mobility and balance issues (ataxia). Loss of feeling and limb weakness (peripheral neuropathy), which is prevalent in people with Leigh syndrome, can make mobility difficult.

Several other characteristics may be present in patients with Leigh syndrome, such as:

  • weakening or paralysis of the muscles that move the eyes (ophthalmoparesis)
  • fast, involuntary eye movements (nystagmus)
  • nerve degeneration that transports information from the eyes to the brain (optic atrophy)

Severe breathing issues are frequent, and they can deteriorate to the point of causing abrupt respiratory failure. Some patients develop thickening of the heart muscle that causes the heart to work harder to pump blood (hypertrophic cardiomyopathy). Furthermore, a chemical known as lactate can accumulate in the body, and high lactate levels are frequently discovered in the blood, urine, or fluid that surrounds and protects the brain and spinal cord (cerebrospinal fluid) of patients with Leigh syndrome.

Signs and symptoms are produced in part by patches of damaged tissue (lesions) that form in the brains of patients with Leigh syndrome. Magnetic resonance imaging detects specific lesions in specific areas of the brain such as the basal ganglia (help govern movement), cerebellum (controls balance and coordination of movement), and brainstem (links the brain to the spinal cord and controls processes such as swallowing and breathing). The loss of the myelin covering surrounding nerves (demyelination) that occurs with brain lesions affects the capacity of the nerves to trigger muscles used for movement or transfer sensory information from the rest of the body back to the brain.

What is the treatment of Leigh syndrome?

Leigh syndrome doesn’t have any cure because it is a genetic disease. Symptomatic treatment is provided for conditions such as seizure, acidosis, and heart problems. Treatment differs from patient to patient because the symptoms may be different. These patients are often placed on vitamins and other supplements.

It is essential to remember that metabolism will be altered, so close monitoring of the food they consume and medications they take is necessary. The use of anesthetic medications may cause severe respiratory distress, so such medications are to be used with caution.

Leigh syndrome is a progressive disease, so regular evaluation with a neurologist, a cardiologist, an audiologist, and an ophthalmologist must be done to identify new symptoms in patients.

Experimental drugs such as dichloroacetate are being tried in some clinics.

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Medically Reviewed on 9/22/2021
References
Leigh's Disease Information Page: https://www.ninds.nih.gov/Disorders/All-Disorders/Leighs-Disease-Information-Page#:~:text=Those%20with%20partial%20deficiencies%20have,with%20Leigh's%20disease%20is%20poor

Leigh syndrome: https://rarediseases.info.nih.gov/diseases/6877/leigh-syndrome/cases/22577