However, some mitochondrial disease aetiologies exhibit a combination of defects in both OXPHOS and FAO, including Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD), Medium-chain acyl-CoA dehydrogenase (MCAD) [37] and acyl-CoA dehydrogenase family member 9 (ACAD9) deficiencies [38,39,40]. Here, ACAD9 is linked to mitochondrial disease.