What are the symptoms? The first problems in young children are often poor weight gain and floppiness. Later, common problems include stiffness or tremor, abnormal eye movements and difficulty swallowing. Some patients have impaired vision or seizures. The disease may also affect the part of the brain that controls breathing, causing patients to require artificial ventilation. What are the causes? Leigh syndrome is caused by changes in the cell’s pathway for producing energy. This process occurs in parts of the cell called mitochondria. The faults can involve several different steps in the energy-producing pathway. How is it diagnosed? Diagnosis of Leigh syndrome is difficult. Scans usually show changes in parts of the brain called the brainstem and basal ganglia. There also tends to be a high level of a chemical called lactic acid in the fluid round the brain called the cerebrospinal fluid (CSF). Tests on muscle and skin biopsies can usually identify the underlying biochemical abnormality and lead to appropriate molecular tests. How is it treated? In the vast majority of patients, there is no effective treatment. Supportive measures are important and may include physiotherapy, muscle relaxants and tube feeding through a gastrostomy. Inheritance patterns and prenatal diagnosis Inheritance patternsLeigh syndrome can show different patterns of inheritance in different families. The patterns include autosomal recessive inheritance and ‘maternal inheritance’, which is due to mutations in mitochondrial DNA. Other cases are caused by new mutations with a very low recurrence risk. Prenatal diagnosisThis is available in some cases of Leigh syndrome, but it is not possible in all cases. Is there support? Information and support in the UK for Leigh syndrome is provided by Climb (see entry Inherited Metabolic diseases).