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.
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. Many factors affect symptom and symptom severity, including what gene mutation is involved. Many genes must work together to ensure that the enzyme, complex II (succinate dehydrogenase), can perform its job normally in the body. Changes in the SDHA, SDHB, SDHC, SDHD, SDHAF1, or SDHAF2 genes can all potentially cause complex II deficiency.
Much of what we know today about the signs and symptoms of complex II deficiency are based on articles which describe individual patients. Due to the rarity of this condition and the complexity of its cause, it is very difficult to predict how a person will be affected. We strongly recommend that you work with your or your child’s healthcare provider to learn more about how the deficiency is affecting your or your child’s health. In the meantime, we have summarized symptoms of complex II deficiency which have been described in case reports:
Inheriting two SDHA gene mutations has caused myoclonic seizures and Leigh’s syndrome. Leigh syndrome is a severe neurological disorder that typically arises in the first year of life. This condition is characterized by progressive loss of mental and movement abilities (psychomotor regression) and typically results in death within a couple of years, usually due to respiratory failure. A small number of people develop symptoms in adulthood or have symptoms that worsen more slowly. The first signs of Leigh syndrome seen in infancy are usually vomiting, diarrhea, and difficulty swallowing (dysphagia) that leads to eating problems. Click here to visit Genetics Home Reference and learn more about Leigh syndrome.
Inheriting two SDHB gene mutations can cause leukodystrophy. Leukodystrophies affect the myelin sheath, the material that surrounds and protects nerve cells. Damage to this sheath slows down or blocks messages between the brain and the rest of the body. This leads to problems with movement, speaking, vision, hearing, and mental and physical development. Most of the leukodystrophies appear during infancy or childhood. They can be hard to detect early because children seem healthy at first. However, symptoms gradually get worse over time. Click here to visit MedlinePlus.gov and learn more about leukodystprohy.
Inheriting two SDHAF1 gene mutations can cause severe progressive leukoencephalopathy beginning in infancy. Leukoencephalopathy refers to the degeneration of the white matter of the brain. It is usually diagnosed by MRI. It causes cognitive impairment, increased muscle tone, and hyperactive reflexes.
Inheriting two SDHD gene mutations can cause progressive loss of mental and movement abilities (psychomotor retardation), and seizures. Signs and symptoms may begin in infancy and progress through childhood.
Complex II deficiency has also been described in association with dilated cardiomyopathy (and heart failure in childhood), hemolytic uremic syndrome and rhabdomyolysis, congenital dislocation of the hip joint, progressive encephalomyopathy (a disorder affecting the brain and skeletal muscle, usually causing weakness) with dementia, and Kearns–Sayre syndrome.
Case reports have also demonstrated that people who have only a single mutation in one of these genes may also be at risk for health problems:
Having one SDHA gene mutation caused optic atrophy, ataxia, proximal myopathy in adulthood.
The Human Phenotype Ontology (HPO) provides the following list of features that have been reported in people with this condition. Much of the information in the HPO comes from Orphanet, a European rare disease database. If available, the list includes a rough estimate of how common a feature is (its frequency). Frequencies are based on a specific study and may not be representative of all studies. You can use the MedlinePlus Medical Dictionary for definitions of the terms below.
|Signs and Symptoms||Approximate number of patients (when available)|
|Abnormal mitochondria in muscle tissue||-|
|Autosomal recessive inheritance||-|
|Decreased activity of mitochondrial complex II||-|
|Increased intramyocellular lipid droplets||-|
|Increased serum lactate||-|
|Ragged-red muscle fibers||-|
|Stress/infection-induced lactic acidosis||-|
Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.
Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.
Nonprofit support and advocacy groups bring together patients, families, medical professionals, and researchers. These groups often raise awareness, provide support, and develop patient-centered information. Many are the driving force behind research for better treatments and possible cures. They can direct people to research, resources, and services. Many groups also have experts who serve as medical advisors. Visit their website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD. Suggest an organization to add.
Living with a genetic or rare disease can impact the daily lives of patients and families. These resources can help families navigate various aspects of living with a rare disease.
These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.
Nutritional Interventions in Primary Mitochondrial Disorders: Developing an Evidence Base
Tuesday, December 2, 2014 -
Wednesday, December 3, 2014
Location: NIH Campus, Bethesda, MD
Description: The goal of this meeting is to explore the use of nutritional interventions, including dietary supplements, in primary mitochondrial disorders (PMD); identify gaps in knowledge; develop a research agenda; and identify research opportunities to promote an evidence base for the use of nutritional interventions in primary mitochondrial disorders.
Contact: Kathryn Camp, MS, RD, CSP,(301) 435-3608, firstname.lastname@example.org
Co-funding Institute(s): Office of Dietary Supplements, Office of Rare Diseases Research
2013 Neurobiology of Disease in Children Symposium: Mitochondrial Disease
Wednesday, October 30, 2013 -
Wednesday, October 30, 2013
Location: Austin, TX
Description: The topic for the 2013 NDC Symposium is Mitochondrial Disease. The NDC Symposium is a forum for preeminent investigators assembled to discuss recent accomplishments and future directions with a large group of child neurologists, program officers from the National Institutes of Health, and members of dedicated foundations and associations.
Co-funding Institute(s): National Institute of Neurological Disorders and Stroke, Office of Rare Diseases Research