African iron overload also known as Bantu siderosis or dietary iron overload is a rare disorder characterized by abnormally elevated levels of iron in the body. The name originates from the initial description of this entity in sub-Saharan Africa, in communities where affected individuals drink a traditional, homemade beer that contains a high amount of iron. Symptoms may vary from case to case but can include the accumulation of fibrous tissue (fibrosis) in the liver and, eventually, scarring of the liver (cirrhosis). The exact cause of African iron overload is unknown, but researchers believe that a combination of dietary and genetic factors results in the development of the disorder.
Researchers originally believed that the popular, iron-rich beer caused cases of African iron overload. However, many individuals that drank the beer did not develop the disorder and some individuals that did not drink the beer did develop it. This led researchers to speculate that a mutation of a gene or genes involved in the transport or breakdown (metabolism) of iron must play a role in the development of African iron overload. Such a gene has not yet been identified.
Causes
African iron overload was originally believed to be caused by individuals who had a diet high in iron, especially individuals in rural African communities that drank a homemade beer with high amounts of iron. However, many individuals in these regions who did not drink excessive amounts of this iron-rich beer also developed African iron overload. Researchers now believe that African iron overload is caused by mutations of an as yet unidentified gene or genes and can be worsened by a diet high in iron.
The most common and best-studied form of inherited iron overload is classical hereditary hemochromatosis, which is caused by mutations of the HFE gene. In the past few decades, researchers have identified separate forms of hemochromatosis and iron overload disorders that occur due to mutations of other iron-related genes. Studies have determined that African iron overload is not related to HFE mutations or any of these other described mutations. More research is necessary to identify the genetic factors that may contribute to the development of this disorder.
The SLC40A1 gene provides instructions for making a protein called ferroportin. This protein is involved in the process of iron absorption in the body. Iron from the diet is absorbed through the walls of the small intestine. Ferroportin then transports iron from the small intestine into the bloodstream, and the iron is carried by the blood to the tissues and organs of the body. Ferroportin also transports iron out of reticuloendothelial cells in the liver, spleen, and bone marrow. The amount of iron absorbed by the body depends on the amount of iron stored and released from intestinal cells and macrophages.
The SLC40A1 gene variation that some studies have associated with increased iron stores in people of African descent may affect the way ferroportin helps to regulate iron absorption in the body. However, researchers suggest that this variation is not associated with most cases of African iron overload.
Diagnosis
A diagnosis of African iron overload is made based upon the identification of characteristic symptoms, a detailed patient history, a thorough clinical evaluation, and a variety of specialized tests such as blood tests, which can reveal elevated levels of ferritin in the blood plasma. Ferritin is a protein that binds to iron and is used as an indicator of the body’s iron stores. Another test measures transferrin saturation. Transferrin is a protein involved in the transport of iron from the intestine into the bloodstream.
Elevation in ferritin concentration without elevation in transferrin saturation does not rule out an iron overload disorder. This combination can be observed in loss-of-function ferroportin mutation and in aceruloplasminemia.[rx] Elevated level of ferritin concentration can be observed in acute or chronic inflammatory processes without pathologic iron overload.[rx]
| Characteristic | Normal range | Unit |
|---|---|---|
| Ferritin-male | 12–300 | ng/mL |
| Ferritin-female | 12–150 | ng/mL |
| Transferrin saturation-male | 10–50 | % |
| Transferrin saturation-female | 15–50 | % |
Ferritin levels above 200 ng/mL (449 pmol/L) in women or 300 ng/mL (674 pmol/L) in men who have no signs of the inflammatory disease need additional testing. Transferrin saturation above the normal range in male and female also need additional testing.[rx]
Chemical evidence of tissue vitamin C deficiency and mild to moderate liver dysfunction are likely to be seen in individuals with African iron overload.[rx] Elevation in gamma-glutamyl transpeptidase can be used as a marker for abnormalities in liver function.
| Characteristic | Normal range | Unit |
|---|---|---|
| Vitamin C | 0.2–2 11–114 |
mg/dL µmol/L |
| Gamma-glutamyl transpeptidase in male | < 55.2 0.92 |
U/l μkat/l |
| Gamma-glutamyl transpeptidase in female | < 37.8 0.63 |
U/l μkat/l |
Treatment
Therapy involving the regular removal of blood via a vein (known as venesection or phlebotomy) is a common therapy for disorders associated with excess iron in the blood and should be beneficial to individuals with African iron overload. Controlled clinical studies of therapeutic phlebotomy for individuals with African iron overload have not been done yet but phlebotomy, if tolerated, is considered by many to be the standard of care.
Genetic counseling may be of benefit for affected individuals and their families.
A person’s hemoglobin is important in the physician’s consideration of iron reduction therapy. A physician can provide therapeutic phlebotomy if the patient’s hemoglobin level is sufficient to sustain blood removal. The physician can also recommend the patient to routinely donate blood. When a patient’s hemoglobin is not sufficient for phlebotomy. Iron reduction will likely require the removal of iron using specific drugs (iron-chelation). The physician may use a combination of these therapies in some situations.[rx]
Investigational Therapies
Additional therapies have been used to treat individuals with disorders of iron overload. Such therapies include iron chelators. Iron chelators are drugs that bind to the excess iron in the body allowing it to be dissolved in water and excreted from the body through the kidneys. More research is necessary to determine the long-term safety and effectiveness of such therapies for individuals with iron overload diseases such as African iron overload.
References
