FASN and hyperinsulinemic hypoglycemia, familial, 4: From an intermediate to late phase of differentiation, folate deficiency significantly enhanced the expression of Cebpα, a transcription factor that binds leptin promotor, and also increased the expression of acetyl-CoA carboxylase 1 (Acc1) and FASN, the key enzymes in the de novo fatty acid biosynthetic pathway.