[Mitochondrial diseases. Clinical features, investigation and genetics].

The aim of this article is to give an overview of mitochondrial disorders. Mitochondria are responsible for the generation of energy in the cells. The term, mitochondrial disorders, usually refers to disorders of the respiratory chain. These disorders can be caused by mutations in the DNA of the mitochondria or in the nuclear DNA. A characteristic feature is that all tissues can be affected, and a defect is expressed differently in different tissues. Highly differentiated energy-demanding tissues, such as neurons and muscle cells, are often affected. Mitochondrial disorders are difficult to diagnose. The investigations comprise metabolic screening, respiratory chain enzyme analysis in muscle tissue, muscle histology, and mutation analysis. The focus of this article is on diagnostic evaluation of childhood disorders, because investigation and diagnosis are particularly difficult in children.