The clinical diagnostic criteria and genetic testing for Friedreich’s ataxia are reviewed from the National Hospital for Neurology and Neurosurgery, Queen Square, London, UK. The essential clinical diagnostic criteria, after Harding, are onset before 25 years, progressive ataxia, absent tendon reflexes, axonopathy, and dysarthria. Additional criteria include scoliosis, cardiomyopathy, optic atrophy, pes cavus, and diabetes. The gene for Friedreich’s ataxia is mapped to chromosome 9q13, with an X25 transcript and GAA mutation repeat in intron 1 of the frataxin gene. The repeat length is correlated with the age at onset and the presence of cardiomyopathy. The frataxin protein may be an iron transporter within the mitochondria. 
COMMENT. A direct genetic test permits diagnosis of Friedreich’s ataxia in forme fruste cases, including those with retained reflexes or onset later than 25 years. The author postulates that the clinical manifestations of Friedreich’s ataxia coupled with the nature of the frataxin protein have the hallmarks of a mitochondrial disease.