Mevalonate Kinase Deficiency (MKD) is a rare, autosomic recessive, metabolic disease, caused by mutations in the MVK gene (12q24.11, NM_000431) coding for the enzyme mevalonate kinase (MK) (E.C. 2.7.1.36), the second enzyme of the mevalonate pathway, the route to cholesterol (Figure 1a) [1,2]. The gene discussed is MVK; the disease is hyperinsulinemic hypoglycemia, familial, 4.