FXN and Friedreich ataxia: This is important because pure GAA repeat expansions are typically identified in humans with FRDA and they might be essential for somatic GAA-repeat-instability-associated disease progression (Montermini et al., 1997), whereas interrupted GAA repeats might induce repeat stability and less severe FXN gene silencing effects, resulting in a milder late-onset FRDA phenotype (McDaniel et al., 2001; Stolle et al., 2008).