Hemojuvelin Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Hemojuvelin and links to relevant pages within the course.
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|Regulation of Iron Equilibrium|
Regulation of iron equilibrium occurs mainly through the process of absorption. Iron is absorbed through the mucosal cells lining the duodenum. A variety of proteins are involved in this process. Hepcidin, an antimicrobial protein primarily produced in the liver, has been recently found to be a major (negative) regulator of dietary iron absorption by disrupting cellular iron transport in the intestine. Decreased levels of hepcidin are related to increased iron absorption into the bloodstream. Hepcidin is increased in response to iron overload and inflammation. (4)Additional proteins involved in iron metabolism include transferrin (Tf), transferrin receptor (TfR), ferroportin, HFE protein, hemojuvelin, and others. Their roles in iron absorption are complex and in some instances incompletely understood.Factors affecting iron absorption include: Tissue stores, e.g., decreased stored iron is associated with a decrease in hepcidin and increase in iron absorption. Rate of hematopoietic activity, e.g., an increased rate of erythropoiesis is associated with a decrease in hepcidin and an increase in iron absorption. Oxygen concentration in tissues, e.g., hypoxia decreases hepcidin and increases iron absorption, thereby promoting increased erythopoiesis. Dietary intake, including form of iron ingested, e.g., heme iron is more readily absorbed than non-heme forms of iron. Condition of GI tract mucosal cells Intraluminal factors, e.g. intestinal motility
|HFE and Other Genes|
A hemochromatosis gene, HFE, was identified in 1996. Mutations in the HFE gene are found in the majority of patients diagnosed with hereditary hemochromatosis (HH). The locus for the gene is on the long arm of chromosome 6 where it codes for a membrane protein, HFE. The exact mechanism of the role of HFE protein in iron metabolism is incompletely understood. It is thought that HFE, along with a second protein, beta-2 microglobin, interacts with transferrin receptors (TfR) on cell membranes. This interaction supresses the affinity of transferrin for TfR, thus lowering the uptake of transferrin--and its attached iron--into the cell. Transferrin receptors have been found on the surface of a variety of cells, with the greatest concentration on cell membranes of intestinal cells, hepatocytes, and RBC precursors. In addition to HFE, HH is also associated with mutations in other genes involved in iron homeostasis, including hemojuvelin (HJV), TfR, hepcidin, and ferroportin. Hepcidin production is reduced in HH due to all of these genetic causes, with a resulting increase in iron absorption. Mutations in HFE are the most common cause of HH.
|Mutations in which gene account for the majority of cases of hereditary hemochromatosis (HH)?||View Page|
Genes in addition to HFE have been linked to hereditary hemochromatosis (HH). They include the hepcidin, hemojuvelin, transferrin receptor, and ferroportin genes. Mutations of some are linked with dominantly inherited HH, juvenile HH, and African iron overload. Unlike HH due to HFE mutations, these clinical disorders are rarely observed in the US population.(9)
The diagnosis of hereditary hemochromatosis (HH) is made through a combination of laboratory tests and medical evaluation of a patient's signs and symptoms. Iron overload is identified by tests that evaluate iron metabolism, while molecular assays are needed to document mutations in the HFE gene or others such as hepcidin, hemojuvelin, or transferrin receptor. Individuals with documented iron overload who exhibit signs and symptoms consistent with HH and who possess HFE or other mutations are considered to have HH. Other causes of secondary iron overload may need to be ruled out.An example of a testing algorithm is shown.