SCO1 and Leigh syndrome: In humans, several mitochondrial disorders caused by mutations in COX assembly factors have been described, presenting with a variety of phenotypes with varying degrees of severity ranging from skeletal myopathies, cardiomyopathies and encephalopathies to Leigh syndrome (LS), with the nuclear genes SURF1, SCO1 and SCO2 being more frequent [11,12,13,14,15].