Hepcidin is an iron-regulatory hepatic peptide hormone encoded by the HAMP gene 
that downregulates iron export from enterocytes and macrophages into the blood 
plasma. In this study, we identified a novel mutation in the HAMP gene of a 
58-year-old Japanese male patient with hemochromatosis. By direct sequencing of 
the five hereditary hemochromatosis-related genes, HFE, HAMP, HJV, TFR2, and 
SLC40A1, the previously unreported p.R75X mutation was identified, and the 
patient was found to be homozygous for the mutation. No other potentially 
pathogenic mutations were detected. In an LC-MS/MS analysis, hepcidin molecules 
were not detected in the patient's serum or urine. These results indicate that 
the p.R75X mutation causes iron overload by impairing the hepcidin system.