BCS1L and hyperinsulinemic hypoglycemia, familial, 4: Isolated oxidative phosphorylation (OXPHOS) deficiencies are relatively rare (i.e., isolated complex III deficiency associated with a defect in the BCS1L gene—GRACILE syndrome (growth retardation, aminoaciduria, cholestasis, iron overload, lactic acidosis, and early death) or isolated complex IV deficiency associated with a defect in the SCO1 gene) [33,34].