The first case of mitochondrial myopathy associated to FDX2 was described in 2014 in a 15-year-old patient with recurrent myoglobinuria, lactic acidosis and slowly progressive muscle weakness due to a homozygous mutation affecting the start codon of FDX2 (c.1A > T, p.Met1Leu) and resulting in a severe reduction of the FDX2 protein levels [95]. The gene discussed is FDX2; the disease is lactic acidosis.