The most common biochemical diagnoses were: isolated complex IV (36 patients, 29.5% of whole series) and complex I (34 pts, 27.9%) deficiencies, followed by isolated complex V deficiency (15 pts, 12.3%), multiple RC defects (15 pts, 12.3%), PDH deficiency (11 pts, 9%) and isolated complex III deficiency (6 pts, 5%). The gene discussed is PDP1; the disease is hyperinsulinemic hypoglycemia, familial, 4.