As about the people with one copy of the H63D alteration (heterozygous carriers), this genotype is very unlikely to cause a clinical presentation, there is no predictable risk of iron overload. Besides that, two 2020 studies revealed that the frequency of homozygous or heterozygous H63D variant is significantly higher in elite endurance athletes comparing to ethnically matched controls, and is associated with high V̇O2max in male athletes. . Each patient with the susceptible genotype accumulates iron at different rates depending on iron intake, the exact nature of the genetic variant, and the presence of other insults to the liver, such as alcohol and viral disease. As such, the degree to which the liver and other organs are affected is highly variable and is dependent on these factors and co-morbidities, as well as age at which they are studied for manifestations of disease. Penetrance differs between populations. Disease-causing genetic variants of the HFE gene account for 90% of the cases of non-transfusion iron overload.This gene is closely linked to the HLA-A3 locus. Pathophysiology
Since the regulation of iron metabolism is still poorly understood, a clear model of how haemochromatosis operates is still not available. A working model describes the defect in the HFE gene, where a mutation puts the intestinal absorption of iron into overdrive. Normally, HFE facilitates the binding of transferrin, which is irons carrier protein in the blood. Transferrin levels are typically elevated at times of iron depletion (low ferritin stimulates the release of transferrin from the liver).
Hereditary haemochromatosis type 1 (HFE-related Hemochromatosis) is a genetic disorder characterized by excessive intestinal absorption of dietary iron, resulting in a pathological increase in total body iron stores. Humans, like most animals, have no means to excrete excess iron, with the exception of menstruation which, for the average woman, results in a loss of 3.2 mg of iron.Excess iron accumulates in tissues and organs, disrupting their normal function. The most susceptible organs include the liver, heart, pancreas, skin, joints, gonads, thyroid and pituitary gland; patients can present with cirrhosis, polyarthropathy, hypogonadism, heart failure, or diabetes.There are 5 types of hereditary hemochromatosis: type 1, 2 (2A, 2B), 3, 4 and 5, all caused by mutated genes. Hereditary hemochromatosis is the most frequent, and unique related to the HFE gene. It is most common among those of Northern European ancestry, in particular those of Celtic descent. The disease is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not express signs or symptoms of the condition. In this situation, the otherwise unaffected parents are referred to as carriers. Signs and symptoms
Haemochromatosis is protean in its manifestations, i.e., often presenting with signs or symptoms suggestive of other diagnoses that affect specific organ systems.