The human Hemochromatosis Protein (HFE) gene is associated with the synthesis of HFE protein. This protein has been shown to be associated with the regulation of the circulating iron by regulating the interaction of the transferrin receptor with transferrin.
The concentration of iron in the blood is detected by a complex of HFE, transferrin receptor 1 and transferrin receptor 2. When diferric (two iron atoms) transferrin binds to transferrin receptor 1, the HFE protein is removed, which then binds to transferrin receptor 2 and triggers the release of hepcidin (a hormone that regulates iron uptake)
Healthy individuals usually take up 8 to 10% of iron from the diet (about 1mg), however, some individuals tend to absorb nearly 4 times more. The additional iron accumulates slowly and leads to a condition known as hemochromatosis
There are many single nucleotide polymorphisms associated with this gene, but we look at two significant polymorphisms which are shown to be associated with the development of hemochromatosis, rs1800562 and rs1799945. Variations of the HFE gene are shown to be associated with a reduction in hepcidin release, which increases the absorption of iron from the intestine and increases the storage of iron in the liver and other tissues.
The variations in the HFE gene that have been shown to increase the absorption, and thereby, storage of iron, were probably adaptations to safeguard against maternal iron deficiency for the fetus.
One of the variations (rs1800562) dates back to a mutation about 6000 years ago, among ancestors of the Celtic population. In this variant (C282Y), tyrosine replaces cytosine, preventing the protein from folding properly. This results in an inability of the HFE protein to bind to transferrin receptor, with reduced production of hepcidin. Only individuals who carry the AA variant of the gene are shown to be associated with iron overload.
Another iron retaining variant of the HFE gene is rs1799945, which developed several thousand years ago in the Basque region in North Spain. This variance is associated with lower iron retention than rs1800562.
Individuals with the AA variant of rs1800562 are at a higher risk for hemochromatosis but the diet consumed and gender play an important role in the extent of iron present in the blood. Men and post-menopausal women are at a higher risk for hemochromatosis, as women in the reproductive age tend to lose iron during their menstrual cycle. Not everyone with the variant allele of this gene develops hemochromatosis, but an understanding of the genotype carried will help in monitoring blood iron levels and watching out for symptoms of iron overload.
The symptoms of iron overload include abdominal pain, memory problems, fatigue, abnormal skin color (ashen-grey) and an irregular heartbeat. Iron overload can also lead to other associated disease conditions like an enlarged heart, liver failure, osteoarthritis and hypogonadism.
The screening threshold for individuals with hereditary hemochromatosis is
In a study conducted on 1657 male and 2077 female patients, people with the AA variant of the gene (rs1800562) were shown to be associated with hereditary hemochromatosis, with higher levels of serum iron and hemoglobin. In another study conducted on menstruating women, the presence of the minor alleles (AA of rs1800562, GG of rs1799945) had a compensatory effect on iron levels)
In a review study conducted on 101,168 participants, individuals with the AA variant of the gene (rs1800562) were shown to be associated with hemochromatosis, with expression of the disease ranging from no evidence of iron overload to organ dysfunction and massive iron overload. 10% of individuals with compound heterozygote (one copy of A variant (rs1800562) and one copy of G variant (rs1799945)) were shown to be associated with mild to moderate iron overload, with severe iron overload associated with viral hepatitis or alcoholism.
Hemoglobin, which are iron containing metalloproteins, are shown to be associated with oxygen transport from the lungs to the rest of the body, which is required to carry out any physical activity. Therefore, Iron deficiency is associated with reduced ability to carry out physical work. Endurance capacity is also lowered among individuals with iron deficiency as there is lowered cellular oxidative capacity due to lowered oxygen transport.
Alternatively, individuals carrying the GG variant of rs1799945, with an increased tendency for iron overload, have an increased potential to boost aerobic capacity among athletes. Many endurance athletes take iron supplements during their active sporting life and a study was conducted to identify if individuals with the HFE variants A(rs1800562) or G (rs1799945) were significantly represented among endurance athletes. The study found that there was a high prevalence of individuals with HFE mutations among endurance athletes than among sedentary controls.
How can this information be used?
It is important to choose an appropriate diet based on the genetic profile
For people with AA variant (rs1800562) and G variant of (rs1799945)- Elevated serum iron levels
For people with G variant (rs1800562) and C variant of (rs1799945)
“Nutrigenetics, fitness genetics, health genetics are all nascent but rapidly growing areas within human genetics. The information provided herein is based on preliminary scientific studies and it is to be read and understood in that context.”