FXN and Friedreich ataxia: Several studies have shown abnormal intracellular iron distribution in Friedreich’s Ataxia, with elevated serum transferrin receptor levels in patients.425,426 In the heart tissue of conditional frataxin knockout mice, increased mRNA levels of MFRN2, SEC15L1, and TFR1 and decreased mRNA levels of FPN1 indicate an activated response to cytoplasmic iron deficiency and increased mitochondrial iron input.