CIAO1 and hyperinsulinemic hypoglycemia, familial, 4: CIAO1 and MMS19 encode proteins indispensable for the maturation and activity of the homodimeric DPD enzyme, which contains 2 FAD, 2 FMN and 8 [4Fe-4S] clusters.19–21 Immunoblot analysis showed severely reduced protein levels of CIAO1 in fibroblasts of patients 1 and 2 compared with fibroblasts of a patient with DPYD deficiency and controls (Figure 2C).