What are the symptoms? Mitochondria are present in nearly every single cell and as a result, any tissue or organ can be involved. Tissues that use a lot of energy, particularly the brain, muscle and heart, are more commonly involved. Some people may have relatively mild symptoms and some people may be more severely affected. Symptoms can include: loss of muscle coordination, muscle weaknessneurological problems, such as seizures (see entry Epilepsy) and memory problemsvisual and/or hearing problemsdevelopmental delayslearning disabilityheart, liver or kidney diseasegastrointestinal disorders, such as severe constipationdiabetes. What are the causes? These conditions are all caused when mitochondria don’t function properly. Mitochondria are often referred to as the ‘powerhouses’ of the cell as their main role is to convert food into energy in the form of adenosine triphosphate (ATP). The mitochondria may be damaged by inherited problems or problems acquired during life. Genetic or inherited mitochondrial diseases occur because of genetic changes in DNA (mutations). These can be inherited in different ways depending on the particular condition. It also depends on whether the genetic change is found in the DNA within the nucleus (nuclear DNA) or the small piece of DNA within the mitochondria (mitochondrial DNA). How is it diagnosed? There is no consistent means of diagnosis. It is sometimes possible to make a diagnosis by performing genetic tests on a blood or urine sample. In some cases, a muscle biopsy (removing a small piece of muscle tissue for analysis) is helpful. How is it treated? Treatment is targeted at relieving symptoms and delaying the progression of the condition. There is no cure at present but research into new treatments is ongoing. Treatment may involve medication, vitamin, and mineral supplements. Some patients respond to certain vitamins, including ubiquinone. Supportive treatments such as physiotherapy and occupational therapy may also be useful. Symptomatic treatment for specific tissue involvement is important. Inheritance patterns and prenatal diagnosis Inheritance patternsThis is particularly complicated for mitochondrial diseases because the genetic instructions needed to make mitochondria are found in both the nuclear DNA and the mitochondrial DNA. Genetic changes in the nuclear DNA can be transmitted by either the mother or the father, whilst genetic changes in the mitochondrial DNA are only transmitted by the mother. Thus, the inheritance pattern of mitochondrial disease will depend upon whether the genetic change is found in the nuclear or mitochondrial DNA. Prenatal diagnosisGenetic counselling for mitochondrial diseases is difficult but very important for families. The advice will vary depending on the genetic change that has been identified. Prenatal diagnosis is available for couples who are at risk of having a child affected by mitochondrial disease but will not be suitable for all. Other reproductive options include in vitro fertilisation (IVF)-based techniques, such as preimplantation genetic diagnosis (PGD) and mitochondrial donation, which was recently approved for clinical use in the UK. Is there support? The Lily Foundation Tel: 0300 400 1234Email: firstname.lastname@example.orgWebsite: thelilyfoundation.org.uk The Foundation is a Registered Charity no.1122071. They provide information and support for children with mitochondrial diseases. They also fund and promote research and aim to raise awareness of mitochondrial diseases. Group details added August 2017. Information and support in the UK for children with mitochondrial diseases and related disorders is provided by Climb (see entry Inherited Metabolic diseases). Information on support in the UK for adults with mitochondrial myopathies and related disorders is provided by the Muscular Dystrophy UK (see entry Congenital Muscular Dystrophy).