What is the definition of Mitochondrial Complex 1 Deficiency?

Mitochondrial complex I deficiency is a type of mitochondrial disease. Mitochondria are specialized compartments in cells that create more than 90% of the energy needed by the body. In mitochondrial diseases, the mitochondria don't work correctly resulting in less energy in the cell, cell injury and cell death. Complex I is the first step in a chain reaction in mitochondria leading to energy production. Signs and symptoms of complex I deficiency vary widely in nature and severity, ranging from lethal neonatal disease to adult-onset neurodegenerative disorders. Features may include macrocephaly (large head) with progressive leukodystrophy, encephalopathy, hypertrophic cardiomyopathy, myopathy, liver disease, Leigh syndrome, Leber hereditary optic neuropathy, and some forms of Parkinson disease. The disease is caused by mutations in any of many genes and the inheritance pattern depends on the responsible gene. Treatment is only helpful in some case but may include metabolic therapies such as riboflavin, thiamine, biotin, co-enzyme Q10, carnitine, and a ketogenic diet (a special high-fat, low-carbohydrate diet). 

What are the alternative names for Mitochondrial Complex 1 Deficiency?

  • Complex 1 mitochondrial respiratory chain deficiency
  • NADH coenzyme Q reductase deficiency
  • Mitochondrial NADH dehydrogenase component of complex I, deficiency of
  • NADH:Q(1) Oxidoreductase deficiency
  • Isolated mitochondrial respiratory chain complex I deficiency
  • Isolated NADH-coenzyme Q reductase deficiency
  • Isolated NADH-CoQ reductase deficiency
  • Isolated NADH-ubiquinone reductase deficiency
  • Isolated complex I deficiency

What is the outlook (prognosis) for Mitochondrial Complex 1 Deficiency?

There can be a lot of variability in the signs, symptoms and severity for people with mitochondrial complex I deficiency. Therefore, the long-term outlook (prognosis) varies among affected people.

In isolated complex I deficiency, the majority of affected people develop symptoms during the first year of life. Most people with this type have a rapidly progressive disease course and do not survive beyond childhood.

In other cases, signs and symptoms can range, causing an affected person to have any of the following:
  • fatal neonatal lactic acidosis - this is typically rapidly progressive, resulting in death in infancy
  • infantile-onset Leigh syndrome - affected children typically have normal early development but develop symptoms in late infancy or early childhood with progressive neurological abnormalities
  • childhood-onset mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome -  symptoms usually begin in childhood with seizures, migraines, vomiting, exercise intolerance, proximal limb weakness and short stature
  • adult-onset syndromes of encephalomyopathy (brain and muscle disease) with variable severity

There have also been some affected people who have had involvement of only one organ (for example, isolated hypertrophic cardiomyopathy (HCM) or Leber hereditary optic neuropathy).

Because not all people with this condition are affected the same way, the life expectancy may differ considerably.

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