mitochondrial complex II deficiency, nuclear type 1
Findings
No curated finding names mitochondrial complex II deficiency, nuclear type 1 yet. Everything below is reference data from Mondo, HPO and GenCC, not evidence about what affects it.
Definition
Complex II deficiency is a 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. The signs and symptoms of mitochondrial complex II deficiency can vary greatly from severe life-threatening symptoms in infancy to muscle disease beginning in adulthood. Complex II deficiency can be caused by mutations in the SDHA, SDHB, SDHD, or SDHAF1 genes. In many cases the underlying gene mutations cannot be identified. Complex II deficiency is inherited in an autosomal recessive fashion. Complex II deficiency gene mutation carriers may be at an increased risk for certain cancers.
Definition from the Mondo Disease Ontology (MONDO:0100294), read 2026-09-29. CC BY 4.0.
- Inheritance
- Autosomal recessive inheritance
- Onset and course
- Infantile onset
HPO, annotations 2026-09-02
Features
55 features
What the disease is reported to present with, and how often among people who have it — never how often a feature means the disease. HPO, annotations 2026-09-02.
- Decreased activity of mitochondrial complex IIHPOHP:0008314
- 3 of 3 reported patients
- Developmental regressionHPOHP:0002376
- 1 of 1 reported patient
- Frequent (30% to 79% of cases)
- Elevated lactate:pyruvate ratioHPOHP:0032653
- 1 of 1 reported patient
- Global developmental delayHPOHP:0001263
- 1 of 1 reported patient
- Increased circulating lactate concentrationHPOHP:0002151
- 1 of 1 reported patient
Genes
4 genes
Germline variants in the gene encoding each protein, as classified by GenCC submitters, each in their own words. Limited, disputed and refuted submissions are listed too.
- SDHAHGNC:10680
- Definitive · G2P · Autosomal recessive · 2025
- Strong · Ambry Genetics · Autosomal recessive · 2025
- Strong · Labcorp Genetics (formerly Invitae) · Autosomal recessive · 2021
- Strong · PanelApp Australia · Autosomal recessive · 2025
- Supportive · Orphanet · Autosomal recessive · 2021
- SDHAF1HGNC:33867
- Strong · Labcorp Genetics (formerly Invitae) · Autosomal recessive · 2021
- Moderate · Ambry Genetics · Autosomal recessive · 2020
- Supportive · Orphanet · Autosomal recessive · 2021
- SDHDHGNC:10683
- Strong · Labcorp Genetics (formerly Invitae) · Autosomal recessive · 2021
- Moderate · Ambry Genetics · Autosomal recessive · 2018
Where it sits
Other names
4 names
Resolves to: mitochondrial complex II deficiency, nuclear type 1
- Also called
- isolated mitochondrial respiratory chain complex II deficiencyisolated succinate-coenzyme Q reductase deficiencyisolated succinate-CoQ reductase deficiencyisolated succinate-ubiquinone reductase deficiency