The mitochondrion and its disorders

© 2003 Blackwell Science Ltd nalling and apoptosis (programmed cell death), and they have a crucial role in metabolism. Many metabolic enzyme systems are contained within mitochondria, including components of tricarboxylic acid (Krebs) cycle enzymes, and the fatty acid β-oxidation pathway. However, the term ‘mitochondrial disorder’ usually refers to a primary abnormality of the mitochondrial respiratory chain. Secondary mitochondrial dysfunction is seen as part of normal ageing and also in neurodegenerative disorders such as Alzheimer’s disease, but the signifi cance of these changes is not clear. Mitochondrial dysfunction also plays an important part in the pathophysiology of a group of inherited neurological diseases that includes Friedreich’s ataxia, Wilson’s disease and hereditary spastic paraparesis. Although related, these are not thought of as ‘primary mitochondrial disorders’ and will not be considered here.