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The gene that controls the amount of iron absorbed from food is called HFE. The HFE gene has two common mutations, C282Y and H63D.[23]
Inheriting just one of the C282Y mutations (heterozygous) makes a person a carrier who can pass this mutation onward. One mutation may lead to slightly excessive iron absorbtion but usually haemochromatosis does not develop.
In the United States, most people with haemochromatosis have inherited two copies of C282Y — one from each parent — and are homozygous for the trait. Mutations of the HFE gene account for 90% of the cases. This gene is closely linked to the HLA-A3 locus. Homozygosity for the C282Y mutation is the most important one, although the heterozygosity C282Y/H63D mutations are also associated to disease (both conditions are sufficient to reach the diagnosis). Carriers of a single copy of either gene have a very slight risk of haemochromatosis when other factors contribute, but are otherwise healthy.[24]
Even if an individual has both copies of the abnormal gene the risk of actual clinical haemochromatosis is low (between 1—25%) due to incomplete penetrance. The variability in these estimates is probably due to different populations studied and how penetrance was defined.[citation needed]
Other genes that cause haemochromatosis are the autosomal dominant SLC11A3/ferroportin 1 gene and TfR2 (transferrin receptor 2). They are much rarer than HFE-haemochromatosis.
Recently, a classification has been developed (with chromosome locations):
* Haemochromatosis type 1 (Mendelian Inheritance in Man (OMIM) 235200): "classical" HFE-haemochromatosis (6p21.3).
* Haemochromatosis type 2 (Mendelian Inheritance in Man (OMIM) 602390): juvenile haemochromatosis :
o Type 2A:(Mendelian Inheritance in Man (OMIM) 602390): mutations in hemojuvelin ("HJV", also known as HFE2)
o Type 2B (Mendelian Inheritance in Man (OMIM) 606464): mutation in hepcidin antimicrobial peptide (HAMP) or HFE2B (19q13)
* Haemochromatosis type 3 (Mendelian Inheritance in Man (OMIM) 604720): transferrin receptor-2 (TFR2 or HFE3, 7q22).
* Haemochromatosis type 4 (Mendelian Inheritance in Man (OMIM) 604653): autosomal dominant haemochromatosis (all others are recessive), ferroportin (SLC11A3) gene mutation (2q32).
Haemochromatosis
The gene that controls the amount of iron absorbed from food is called HFE. The HFE gene has two common mutations, C282Y and H63D.
Inheriting just one of the C282Y mutations (heterozygous) makes a person a carrier who can pass this mutation onward. One mutation may lead to slightly excessive iron absorbtion but usually haemochromatosis does not develop.
In the United States, most people with haemochromatosis have inherited two copies of C282Y — one from each parent — and are homozygous for the trait. Mutations of the HFE gene account for 90% of the cases. This gene is closely linked to the HLA-A3 locus. Homozygosity for the C282Y mutation is the most important one, although the heterozygosity C282Y/H63D mutations are also associated to disease (both conditions are sufficient to reach the diagnosis). Carriers of a single copy of either gene have a very slight risk of haemochromatosis when other factors contribute, but are otherwise healthy.
Even if an individual has both copies of the abnormal gene the risk of actual clinical haemochromatosis is low (between 1—25%) due to incomplete penetrance. The variability in these estimates is probably due to different populations studied and how penetrance was defined.
Other genes that cause haemochromatosis are the autosomal dominant SLC11A3/ferroportin 1 gene and TfR2 (transferrin receptor 2). They are much rarer than HFE-haemochromatosis.
Recently, a classification has been developed (with chromosome locations):
* Haemochromatosis type 1 (Mendelian Inheritance in Man (OMIM) 235200): "classical" HFE-haemochromatosis (6p21.3).
* Haemochromatosis type 2 (Mendelian Inheritance in Man (OMIM) 602390): juvenile haemochromatosis :
o Type 2A:(Mendelian Inheritance in Man (OMIM) 602390): mutations in hemojuvelin ("HJV", also known as HFE2)
o Type 2B (Mendelian Inheritance in Man (OMIM) 606464): mutation in hepcidin antimicrobial peptide (HAMP) or HFE2B (19q13)
* Haemochromatosis type 3 (Mendelian Inheritance in Man (OMIM) 604720): transferrin receptor-2 (TFR2 or HFE3, 7q22).
* Haemochromatosis type 4 (Mendelian Inheritance in Man (OMIM) 604653): autosomal dominant haemochromatosis (all others are recessive), ferroportin (SLC11A3) gene mutation (2q32).
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