DGUOK deficiency is a very rare disorder characterized by liver dysfunction (jaundice, cholestasis, hepatomegaly, and elevated transaminases), neurological manifestations (hypotonia, nystagmus, opsoclonus, and psychomotor retardation), and metabolic disorders (lactic acidosis or hypoglycemia) secondary to severely reduced mtDNA. The gene discussed is DGUOK; the disease is hyperinsulinemic hypoglycemia, familial, 4.