<p>Frataxin is a mitochondrial protein, mutation of which leads to the disease Friedreich's ataxia [<cite idref="PUB00005550"/>]. Its orthologs are widely distributed in the bacteria, associated with the ISC system for iron-sulphur cluster assembly, and designated CyaY. Friedreich's ataxia is a progressive neurodegenerative disorder caused by loss of function mutations in the gene encoding frataxin (FRDA). Frataxin mRNA is predominantly expressed in tissues with a high metabolic rate (including liver, kidney, brown fat and heart). Mouse and yeast frataxin homologues contain a potential N-terminal mitochondrial targeting sequence, and human frataxin has been observed to co-localise with a mitochondrial protein. Furthermore, disruption of the yeast gene has been shown to result in mitochondrial dysfunction. Friedreich's ataxia is thus believed to be a mitochondrial disease caused by a mutation in the nuclear genome (specifically, expansion of an intronic GAA triplet repeat) [<cite idref="PUB00005217"/>, <cite idref="PUB00004328"/>, <cite idref="PUB00003904"/>].</p>