Disturbance in any one of the hepcidin regulatory proteins, including the HFE, Tf receptor 2 (TfR2), hemojuvelin (Hjv), bone morphogenetic srotein 6 (BMP6), matriptase-2, neogenin, and transferrin (Tf) causes inappropriate regulation of its expression and consequently results in either iron overload or iron deficiency. Here, BMP6 is linked to Tangier disease.