In 1999, Drenth et al. identified mutations in the gene encoding mevalonate kinase (MVK), the key enzyme in isoprenoid and sterol synthesis, which is involved in the pathogenesis of mevalonate kinase deficiency (MKD) and hyperimmunoglobulinemia D syndrome (HIDS) [5]. Here, MVK is linked to hyperinsulinemic hypoglycemia, familial, 4.