There were gender differences in serum FGF-21 levels [men (n = 17), median 261.4 pg/ml (interquartile range 17.5–1707] vs. women (n = 15), 442.4 pg/ml (25.2–1,599.1) among patients with primary MIDs, and there were no gender differences in serum FGF-21 levels [men (n = 9), median 69.2 pg/ml (interquartile range 23.9–81.8) vs. women (n = 6), 75.1 pg/ml (36.9–93.4) in FA patients] (Table 1). Here, FGF21 is linked to Friedreich ataxia.