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What is mitochondrial disease?
Mitochondrial disease is caused by problems with the mitochondria, which are tiny structures inside almost every cell in the body. Their main job is to produce energy that cells need to work properly.
If mitochondria do not work as they should, cells cannot make enough energy. This can affect organs and tissues that need lots of energy, such as the brain, muscles, heart and liver.
Genetic causes
Most mitochondrial diseases are caused by changes, or mutations, in genes. These genes give instructions for making proteins needed for the mitochondria to function.
The faulty gene may be inherited from one or both parents. In some cases, the change happens for the first time in the affected person and is not passed down from a parent.
Mitochondrial disease can be inherited in different ways. Some conditions are passed through the mother’s mitochondrial DNA, while others are caused by changes in genes in the cell nucleus.
Why different people are affected in different ways
Not everyone with a mitochondrial gene change will be affected in the same way. This is because cells can contain a mix of healthy and faulty mitochondria.
The balance between normal and abnormal mitochondria can influence how severe the symptoms are. It can also affect which parts of the body are most impacted.
This is one reason mitochondrial disease can look very different from person to person. Some people have mild symptoms, while others are much more seriously affected.
Can it be caused by other factors?
Mitochondrial disease itself is usually genetic, but symptoms can sometimes be triggered or made worse by illness, stress or certain medicines. These factors do not usually cause the condition, but they may bring symptoms to attention.
In rare cases, damage to mitochondria may happen later in life due to other medical conditions or environmental factors. However, this is different from inherited mitochondrial disease.
When to seek help
If someone has symptoms such as muscle weakness, tiredness, headaches, learning difficulties, seizures or problems with balance, it may be worth discussing this with a GP. These symptoms can have many causes, not just mitochondrial disease.
In the UK, a GP can refer someone for specialist assessment and genetic testing if mitochondrial disease is suspected. Early diagnosis can help with management, support and family planning.
Frequently Asked Questions
The main mitochondrial disease causes include mutations in mitochondrial DNA, mutations in nuclear genes that affect mitochondrial function, and, less commonly, large-scale deletions or rearrangements of mitochondrial DNA.
Mitochondrial disease causes can come from either mitochondrial DNA or nuclear DNA. Mitochondrial DNA causes are inherited only from the mother in most cases, while nuclear DNA causes can be inherited from either parent.
Yes. Inherited mutations are a major category of mitochondrial disease causes. These can be passed through maternal inheritance for mitochondrial DNA or through autosomal or X-linked inheritance for nuclear gene defects.
Yes. Spontaneous, or de novo, mutations can be mitochondrial disease causes when they arise for the first time in a person rather than being inherited from a parent.
Yes. Deletions in mitochondrial DNA are recognized mitochondrial disease causes and can reduce the cell's ability to produce energy efficiently.
Yes. Mutations in nuclear genes are common mitochondrial disease causes because many proteins needed for mitochondrial function are encoded by nuclear DNA.
Yes. Many mitochondrial disease causes impair oxidative phosphorylation, which is the process cells use to make most of their energy in the form of ATP.
Yes. Maternal inheritance is a classic pattern among mitochondrial disease causes when the mutation is in mitochondrial DNA, because mitochondria are usually inherited from the mother.
Yes. Mitochondrial disease causes can show variable effects among family members because of heteroplasmy, differing mutation levels, and tissue-specific vulnerability.
Heteroplasmy is the presence of a mixture of normal and mutated mitochondrial DNA in a cell, and it can influence how strongly mitochondrial disease causes affect a person.
Yes. Defects in mitochondrial protein synthesis are important mitochondrial disease causes because mitochondria need properly made proteins to generate energy and maintain function.
Yes. Problems with mitochondrial maintenance and replication are recognized mitochondrial disease causes, especially when nuclear genes that support mitochondrial DNA stability are affected.
Environmental factors are usually not the primary mitochondrial disease causes, but they can worsen symptoms or unmask an underlying genetic mitochondrial disorder.
Toxins are generally not considered the underlying mitochondrial disease causes in inherited cases, but certain toxins and medications can damage mitochondrial function and mimic or aggravate disease.
Yes. Defects in enzymes involved in the respiratory chain, the Krebs cycle, or other mitochondrial pathways can be mitochondrial disease causes.
Yes. Oxidative phosphorylation defects are among the most important mitochondrial disease causes because they directly reduce the cell's ability to produce ATP.
Yes. Many mitochondrial disease causes are genetic and present from birth, although symptoms may appear in infancy, childhood, or adulthood.
Age-related mitochondrial DNA damage is not usually the primary cause of inherited mitochondrial disease, but it can contribute to declining mitochondrial function over time.
Yes. Because mitochondria are needed in nearly every tissue, mitochondrial disease causes can lead to multisystem disease affecting the brain, muscles, heart, eyes, liver, and kidneys.
Doctors identify mitochondrial disease causes through medical history, physical examination, family history, laboratory testing, and genetic testing of mitochondrial DNA and nuclear DNA.
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