Mitochondrial complex II deficiency

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Mitochondrial complex II deficiency
Other names: Succinate dehydrogenase deficiency,Complex 2 mitochondrial respiratory chain deficiency,Succinate CoQ reductase deficiency,Mitochondrial respiratory chain complex II deficiency[1]
Depiction of two autozygous regions on chromosome 11 including a 2.37Mb region containing 21 genes which include SDHD
SpecialtyMedical genetics
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Mitochondrial complex II deficiency, also called CII deficiency, is a rare mitochondrial disease. As of 2013, about thirty-six cases had been reported.[2]

Signs and symptoms

Mitochondrial complex II deficiency affects the body's mitochondria[3] and can have a variety of presentations. In some cases, the brain, heart, liver, kidneys, and muscles are affected, while in other cases, only the heart and muscles are affected with adult onset.[4] Common symptoms include the Babinski sign, muscle weakness, distal amyotrophy (muscle wasting of the limbs), developmental regression (loss of developmental milestones), and being easy to fatigue.[3]


CII deficiency is a genetic disorder with autosomal recessive inheritance,[4] meaning that a person must inherit a genetic mutation from each parent to be affected.[3] Said mutation may be in the SDHAF1 gene on chromosome 19q13, SDHD gene on chromosome 11q23 or SDHB gene on chromosome 1p36 (for each respective type).[4]


The most effective way to diagnose CII deficiency is by measuring the activity of complex II in the muscles.[4]


In terms of mitochondrial complex II deficiency, treatment with riboflavin might offer clinical improvement[4]


In more severe cases where multiple organ systems are affected, death can occur in early life due to multisystem failure.[2]


  1. "GARD Rare Disease Information - Mitochondrial complex II deficiency - National Organization for Rare Disorders". 16 June 2022. Archived from the original on 17 August 2022. Retrieved 21 October 2023.
  2. 2.0 2.1 Sciacovelli, Marco; Schmidt, Christina; Maher, Eamonn R.; Frezza, Christian (2020). "Metabolic Drivers in Hereditary Cancer Syndromes". Annual Review of Cancer Biology. 4: 77–97. doi:10.1146/annurev-cancerbio-030419-033612.
  3. 3.0 3.1 3.2 "Mitochondrial complex II deficiency". Genetic and Rare Diseases Information Center. Archived from the original on 25 June 2020. Retrieved 25 June 2020.
  4. 4.0 4.1 4.2 4.3 4.4 "MITOCHONDRIAL COMPLEX II DEFICIENCY". OMIM. Archived from the original on 28 June 2020. Retrieved 25 June 2020.