Defects in the mitochondrial β-oxidation pathway elicit clinically heterogeneous myopathies resulting from either multiple acyl-CoA dehydrogenase deficiency (MADD), an autosomal recessive disorder caused by mutations in ETFDH, a gene encoding electron-transfer flavoprotein: ubiquinone oxidoreductase, or mutations in ETFA or ETFB, which encode the alpha or beta subunit of electron transfer flavoprotein (ETF) [8,9]. Here, ETFDH is linked to multiple acyl-CoA dehydrogenase deficiency.