Interestingly, 7 patients presented normal lactate levels both in plasma and CSF: 4 were genetically defined, harboring mutations in the MT-ND5, MT-ATP6, BCS1L, GFM1 genes, and 3 patients, lacking a defined genetic diagnosis, showed one of the following biochemical defects: pyruvate dehydrogenase (PDH) deficiency, complex III deficiency and multiple complexes deficiency (I–III). The gene discussed is GFM1; the disease is hyperinsulinemic hypoglycemia, familial, 4.