Haemochromatosis

From Academic Kids

Haemochromatosis, also spelled hemochromatosis, is a hereditary disease characterized by improper processing by the body of dietary iron which causes iron to accumulate in a number of body tissues, eventually causing organ dysfunction. It is the main iron overload disorder.

Contents

Signs and symptoms

Haemochromatosis is notoriously protean, i.e. it presents with symptoms that are often initially attributed to other diseases.

Symptoms may include:

Males are usually diagnosed after their forties, and women about a decade later, owing to regular iron loss by menstruation (which ceases in menopause).

Diagnosis

Imaging features

Clinically the disease may be silent, but characteristic radiological features may point to the diagnosis. The increased iron stores in the organs involved, especially in the liver and pancreas, result in an increased attenuation at unenhanced CT and an decreased signal intensity at MR imaging. Hemochromatosis arthropathy includes degenerative osteoarthritis and chondrocalcinosis. The distribution of the arthropathy is distinctive, but not unique, frequently affecting the second and third metacarpophalangeal joints of the hand.

Chemistry

A first step is the measurement of ferritin, the tissue form of accumulated iron which is shed into the blood. Other markers of iron metabolism are the iron carrying protein transferrin (decreased), transferrin saturation (increased) and serum iron (increased). Genetic testing is performed if the biochemical markers are deranged.

Other blood tests routinely performed: blood count, renal function, liver enzymes, electrolytes, glucose (and/or an oral glucose tolerance test (OGTT)).

Based on the history, the doctor might consider specific tests to monitor organ dysfunction, such as an echocardiogram for heart failure.

Histopathology

When these investigations point at haemochromatosis, it is debatable whether a liver biopsy still needs to occur to quantify the amount of accumulated iron.

Genetics and epidemiology

Haemochromatosis is one the most common inheritable genetic defects, especially in people of northern European extraction, with about 1 in 10 people carrying the defective gene. The prevalence of haemochromatosis varies in different populations. In Northern Europeans it is of the order of one in 400 persons. Other populations probably have a lower prevalence of this disease. It is presumed, though genetic studies, that the "first" haemochromatosis patient, possibly of Celtic ethnicity, lived 60-70 generations ago. Around that time, when diet was poor, the presence of a mutant allelle may have provided a heterozygous advantage in maintaining sufficient iron levels in the blood. With our current rich diets, this 'extra help' is unnecessary and indeed harmful.

Mutations of the HFE gene account for 90% of the cases. Homozygosity for the C282Y mutation is the most important one, although the H63D mutation can contribute to disease (substantially less than C282Y). 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 still quite low (? about 20%). This is called incomplete penetrance.

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 (Template:OMIM): "classical" HFE-haemochromatosis (6p21.3).
  • Haemochromatosis type 2 (Template:OMIM): juvenile haemochromatosis :
    • Type 2A: tentatively called HFE2A (1q21)
    • Type 2B (Template:OMIM): mutation in hepcidin antimicrobial peptide (HAMP) or HFE2B (19q13)
  • Haemochromatosis type 3 (Template:OMIM): transferrin receptor-2 (TFR2 or HFE3, 7q22).
  • Haemochromatosis type 4 (Template:OMIM): autosomal dominant haemochromatosis (all others are recessive), ferroportin (SLC11A3) gene mutation (2q32).

Pathophysiology

The normal distribution of body iron stores
The normal distribution of body iron stores

People with the abnormal genes do not reduce their absorption of iron in response to increased iron levels in the body. Thus the iron stores of the body increase. As they increase the iron which is initially stored as ferritin starts to get stored as a breakdown product of ferritin called haemosiderin and this is toxic to tissue.

Treatment

Early diagnosis is important because the late effects of iron accumulation can be wholly prevented by periodic phlebotomies (comparable in volume to blood donations). Treatment is initiated when ferritin levels reach 300 micrograms per litre (or 200 in nonpregnant premenopausal women).

Every bag of blood (450-500 ml) contains 200-250 milligrams of iron. Phlebotomy is usually done at a weekly interval until ferritin levels have returned to normal. After that, 1-4 donations per year are usually needed to maintain iron balance.

Other parts of the treatment include:

Screening

According to some, a one-time study of iron levels early in adult life would be sufficient to evaluate an individual. There is, however, a tendency for iron to accumulate over time. It is therefore doubtful whether screening should be undertaken at all, irrespective of timing problems. Only the most severe cases would be detected by a one-time ferritin check.

Differential diagnosis

There exist other causes of excess iron accumulation, which have to be considered before Haemochromatosis is diagnosed.

  • Transfusion haemosiderosis is the accumulation of iron, mainly in the liver, in patients who receive frequent blood transfusions (such as those with thalassemia).
  • Dyserythropoeisis is a disorder in the production of red blood cells. This leads to increased iron recycling from the bone marrow and accumulation in the liver.
  • Bantu haemosiderosis occurs in the Bantu population in Southern Africa. This is due to the fact that beer is kept in ungalvanised barrels, leading to increased oxidation and increased iron levels in the beer.

History

The disease was first described by Armand Trousseau (Biography (http://www.whonamedit.com/doctor.cfm/2490.html)) in an article on diabetes: Glycosurie, diabète sucré. Clinique médicale de l'Hôtel-Dieu de Paris, 2nd ed, Paris, 1865, 2: 663-698. He did not make the link with iron accumulation. This was done by Daniel von Recklinghausen (Biography (http://www.whonamedit.com/doctor.cfm/1174.html)) in Hämochromatose. Tageblatt der Naturforschenden Versammlung 1889. Heidelberg, 1890:324.

See also

External link:


Health science - Medicine - Hematology
Hematological malignancy and White blood cells
Leukemia (ALL, AML, CLL, CML) - Lymphoma (Hodgkin's disease, NHL) - Multiple myeloma - MDS - Myelofibrosis - Myeloproliferative disease (Essential thrombocytosis, Polycythemia) - Neutropenia
Red blood cells
Anemia - Hemochromatosis - Sickle-cell anemia - Thalassemia - G6PD - other hemoglobinopathies
Coagulation and Platelets
Thrombosis - Deep venous thrombosis - Pulmonary embolism - Hemophilia - ITP - TTP
nl:Hemochromatose

fr:hémochromatose génétique

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