GTR Home > Conditions/Phenotypes > Mitochondrial complex II deficiency


Complex II, also known as succinate dehydrogenase (EC, is part of the mitochondrial respiratory chain. Deficiency of complex II is characterized by highly variable phenotypic expression. [from OMIM]

Associated genes

Clinical features

  • Babinski sign
  • Muscle weakness
  • Hyperreflexia
  • Short stature
  • Neonatal hypotonia
  • Increased serum lactate
  • Developmental regression
  • Progressive leukoencephalopathy
  • Cognitive impairment
  • Seizures
  • Ragged-red muscle fibers
  • Ataxia
  • Spasticity
  • Dystonia
  • Myoclonus
  • Flexion contracture
  • Hypertrophic cardiomyopathy
  • Dilated cardiomyopathy
  • Leukoencephalopathy
  • Exercise intolerance
  • Stress/infection-induced lactic acidosis
  • Decreased activity of mitochondrial complex II
  • Abnormal mitochondria in muscle tissue
  • Increased intramyocellular lipid droplets
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