FXN and Friedreich ataxia: Friedreich’s ataxia (FRDA) is an autosomal recessive disease caused primarily by an intronic GAA triplet expansion in the FXN gene, leading to reduced expression of full-length frataxin protein (Lynch et al., 2002) and the mitochondrial processing peptidase (MPP)-derived mature frataxin (Condo et al., 2007; Schmucker et al., 2008b).