AbstractBackground:Friedreich ataxia is an autosomal recessive disorder caused by mutations in the frataxin gene, leading to reduced levels of the mitochondrial protein frataxin. Assays to quantitatively measure frataxin in peripheral blood have been established. To determine the validity of frataxin as a biomarker for clinical trials, we assessed frataxin in clinically affected tissue.Methods:In 7 patients with Friedreich ataxia, frataxin content was measured in blood and skeletal muscle before and after treatment with recombinant human erythropoietin, applying the electrochemiluminescence immunoassay.Results:We found frataxin content to be correlated in peripheral blood mononuclear cells and skeletal muscle in drug‐naive patients with Friedreich ataxia. The correlation of frataxin content in both compartments remained significant after 8 weeks of treatment. Skeletal‐muscle frataxin values correlated with ataxia using the Scale for the Assessment and Rating of Ataxia score.Conclusions:Our results endorse frataxin measurements in peripheral blood cells as a valid biomarker in Friedreich ataxia. © 2011 Movement Disorder Society