FXN and Friedreich ataxia: Friedreich ataxia (FRDA, OMIM #229300) is the most common inherited form of ataxia (1:50,000 individuals), caused by the abnormal expansion of the GAA repeat sequence in intron 1 of the FXN gene located on chromosome 9 (position 9q21.11), leading to reduced levels of frataxin, a mitochondrial protein involved in iron–sulfur cluster biosynthesis and crucial for mitochondrial energy production and protection against oxidative stress [1].