HLCS deficiency was first known as early-onset MCD because most patients present first clinical manifestations in the neonatal period or early infancy with a variety of symptoms, including skin lesions, vomiting, hypotonia, drowsiness, seizure, metabolic acidosis, hyperammonemia, and developmental delay [4, 7, 8]. The gene discussed is HLCS; the disease is hyperinsulinemic hypoglycemia, familial, 4.