IRON DISORDERS GENESCREEN

Haemochromatosis has been classified as the most common genetic disorder worldwide. In Caucasian populations, approximately one in ten people carry a faulty gene which, when inherited from both parents, could lead to iron overload if preventative measures (e.g. phlebotomy) are not implemented at an early stage.

Reducing the risk of cancer, heart disease, diabetes, arthritis, infertility and many other complications of organ damage due to overabsorption of iron from the diet has become a health priority. Therefore, our pathology supported Haemochromatosis Test does not only focus on the identification or exclusion of genetic risk factors, but also the documentation of clinical conditions, abnormal biochemistry and environmental factors that may influence disease development.

Hereditary Iron overload

Clinical characteristics

Symptoms of inherited iron overload include:

• Chronic parenchymal liver disease, cirrhosis, hepatocellular carcinoma
• Cardiomyopathy and arrhythmias
• Diabetes mellitus type I and I
• Infertility, amenorrhoea (no periods), impotence, loss of libido, testicular atrophy
• Anterior pituitary failure
• Arthritis, arthralgia, joint pain
• Porphyria cutanea tarda
• Weakness, chronic fatigue
• Mood swings, depression
• Unexplained abdominal pain, frequent diarrhoea
• Skin pigmentation, bronzing of the skin
• Loss of body hair

Prevalence – who is at risk?

The carrier frequency of the most common mutation underlying hereditary haemochromatosis (HH), C282Y in the HFE gene, is about 1 in 6 in the Caucasian population of South Africa. This means that approximately 1 in 100 (estimated 1/115) individuals of European descent will inherit two copies of the defective gene (de Villiers et al. 1999 a,b). It is uncertain what percentage of these individuals will develop organ damage, as the disease penetrance varies from less than 1% on the one extreme in some populations, to between 40-60% depending on the phenotype considered, genetic background and environmental exposures. Gender is also important as females are usually affected about 10 years later than males due to iron loss through menstruation and childbearing.

Many experts do not recommend population screening for detection of abnormal iron-loading genes, because of the low penetrance of the most common late-onset form of haemochromatosis. However, extending genetic investigations to family members of an affected individual may allow accurate genetic diagnosis in the initial asymptomatic phase. Early clinical symptoms include chronic fatigue, joint and muscle pain, etc. An argument for genetic screening of people known to be from high risk populations (e.g. people originating from North Western Europe) has been made and may in some areas be justified. Obviously, individuals with a genetic predisposition for inherited iron overload must have their iron status determined to assess possible gene expression and to monitor response to treatment, if indicated.

Diagnosis of haemochromatosis

The latest classification of hereditary iron overload disorders broadly divides them into HFE-related haemochromatosis, which constitutes about 90% of cases, and non-HFE-related haemochromatosis. Five categories based on different genetic mutations and clinical presentation can be discerned (Brissot et al. 2008):

• Type 1 is classic haemochromatosis, where the affected persons are most often homozygous for the C282Y a mutation in the HFE gene causing a substitution of tyrosine for cystine at amino acid 282 in its product.
• Type 2A (with mutations in the HJV gene, encoding the hemojuvelin protein) and 2B (mutations in the HAMP gene that encodes hepcidin), both presenting at 20-30 years of age
• Type 3 (mutations in the TFR2 gene, encoding the transferrin receptor 2)
• Type 4 (mutations in the SLC40A1gene, encoding ferroportin)
• A(hypo)ceruloplasminemia (a rare autosomal recessive form)

Types 1 to 3 have autosomal recessive inheritance patterns and manifest as parenchymal iron overload with organ failure, targeting mainly the liver, heart and endocrine organs. Type 4 is autosomal dominant and manifests as storage (macrophagal) iron overload.

Hepcidin, the hepatic-derived 25-amino acid peptide has now been recognized to play a key role in the regulation of iron homeostasis. The products of the genes that are associated with the 4 major types of haemochromatosis discussed above, all exert either regulatory effects on the synthesis or affect the function of hepcidin. Most of the clinical, biochemical and pathological features of iron overload disorders can now be explained by hepcidin deficiency or failure.

Inheritance pattern

Except for one rare form of adult-onset haemochromatosis caused by mutations in the ferroportin gene, inherited iron overload follows an autosomal recessive inheritance pattern. This means that patients with haemochromatosis have inherited a defective copy of the gene from both parents. The most common form is caused by mutations in the HFE gene on chromosome 6. Three mutations (HFE C282Y, H63D and S65C) account for the disease in the majority of affected patients.

People with one copy of a defective HFE gene are called heterozygotes or carriers. Mutation carriers do not necessarily develop clinical symptoms and the gene can be passed on in a family without any one being aware of it. Children of two mutation carriers have a 25% chance of inheriting two copies of the defective gene. Those who inherit a defective copy of the gene from both parents are homozygous and are likely to develop the disease whereas those who inherit from one parent are carriers who are unaffected or may show a lesser increase in iron absorption.

Knowledge about the inherited nature of haemochromatosis and the application of genetic testing is important, because the disease goes undetected in many patients especially in the early preventable phase due to the non-specific symptoms of iron overload such as fatigue, joint aches, abdominal pain, loss of libido and depression.

Genetic testing

Genetic testing is important since it can provide a definitive diagnosis of inherited iron overload without the necessity of an invasive liver biopsy. Several polymerase chain reaction (PCR)-based methods have been developed for detection of mutations underlying haemochromatosis, including a reverse-hybridisation method that allows simultaneous analysis of multiple mutations in a single reaction (Oberkanins et al. 2000; Kotze et al. 2004). Today real-time PCR are mostly used for mutation detection in patients at risk of haemochromatosis. An important consideration in the test design is to be aware of the fact that certain gene regions of relevance to PCR-based tests frequently contain non-functional sequence changes that may interfere with the test procedure and data interpretation (de Villiers and Kotze 1999).

Patients are usually referred for genetic testing to confirm or exclude clinical/biochemical diagnosis, assess carrier status in families or for pre-clinical diagnosis in at-risk family members. To facilitate interpretation of genetic test results, information on clinical symptoms and iron parameters has to be provided when patients are referred for genetic testing.

Treatment

It may be necessary to treat patients with iron overload according to the genetic subtype: venesection is the treatment of choice in patients with haemochromatosis related to hepcidin deficiency, but is poorly tolerated or contraindicated in patients with iron overload due to ferroportin failure.

Standard treatment for HH patients with high transferrin saturation and ferritin levels involve weekly therapeutic phlebotomy of 500 ml whole blood (equivalent to approximately 250 mg iron) (Pietrangelo 2004). Regular venesection should be continued until ferritin levels are <50 ng/ml and transferrin saturation <30%. Although some patients with HH, for reasons that are unclear at this time, do not reaccumulate iron, most patients will require maintenance phlebotomy of 1 unit of blood to be removed every 2-3 months.

Genetic counselling

Genetic counselling forms an important aspect of genetic testing, although the level of counselling may differ according to the type of test offered. In patients with haemochromatosis the inheritance pattern of the condition and the risk of close family members to inherit and/or develop the disease is explained. It is made clear that haemochromatosis it is a treatable and even preventable disease if diagnosed at an early stage. It is furthermore explained that medical management such as phlebotomy in those diagnosed with HH or regular blood donation in healthy individuals with a genetic predisposition will reduce future risk of iron overload. Also, mutation carriers with only a single copy of a recessive gene will not develop haemochromatosis, but future generations may be affected. Family members without a HH mutation cannot transfer the determinant gene defect(s) to their children and have a risk similar to that of the general population.

As mutation carriers (in the case of the recessive forms of haemochromatosis) do not necessarily develop clinical symptoms the defective gene can be passed on in a family unnoticed. Offspring of two mutation carriers will have a 25% (1 in 4) chance of inheriting two copies of the defective gene. Since organ damage occur in approximately 40-60% of individuals with a genetic predisposition for haemochromatosis, it is important that testing is offered to all relatives of an HH sufferer (Milani and Kotze 1999). The risk is increased if a family history of arthritis, diabetes, liver disease or heart failure is present.

Frequently asked questions

Genetic testing is very important to identify haemochromatosis at an early, preventable stage. In patients with serum ferritin levels above 1000 ng/ml the risk of liver cirrhosis is very high.

Increased iron levels occur in approximately 50% of women and 80% of men who with two copies of the most common HFE gene mutation, C282Y. However, in some population clinical expression of this genotype is less than 1% due to gene-gene and gene-environment interaction. Reduced penetrance is caused by interaction with other genes and the environment, which explains why it is possible to prevent this condition. If iron levels builds up to dangerous levels, it poisons the affected person from within.

A simple iron count, including a transferrin saturation (>45%) and serum ferritin test (>300 ng/ml), will show whether a person has too much iron in their blood. A DNA test can detect an increased risk of iron overload even before iron stores increase with age, which provides the opportunity for disease prevention. A positive DNA test in the presence of high iron levels confirms a diagnosis of haemochromatosis without the need to perform a liver biopsy. Determination of serum ferritin and transferrin saturation is recommended as a first line screening method for haemochromatosis in patients with clinical features suggestive of this condition. If haemochromatosis is not diagnosed early, it can lead to organ damage.

2) What effect does the typical South African diet has on disease expression?

A person’s diet alone cannot control the iron overload or used for treatment of the condition, but it can help manage the uptake of iron and delay phlebotomy intervals. The use of vitamin C with red meat increases iron absorpsion and should be avoided in HH suffers. Restrict (red) meat and alcohol intake, encourage fibres, tannin, anti-oxidants (green tea). Most importantly, haemochromatosis patients should not take iron tablets or other forms of food supplements containing iron.

The low penetrance of clinically manifested haemochromatosis described in some European populations may not apply to African populations that consume lots of red meat, food cooked in iron pots or beer brewed in iron containers in rural areas.

Typically, Blood Services in South Africa will accept blood from haemochromatosis patients who are on a maintenance program, which requires them to be bled at intervals of more than 56 days. Patients on maintenance will be accepted in the same way as any other donor. When a person requires to be bled more frequently than the normal interval required by the Blood Services, there are restrictions and there may be a cost for the bleed. It is advisable to confirm the detailed arrangements with the local blood services.

The possibility of haemochromatosis should always be considered when a doctor encounter patients with unexplained mild changes in liver function, abnormal tiredness, right hypochondrial pain, arthritis, diabetes, impotence (particularly if they are young), and unexplained cardiac complaints – particularly if more than one of these are present.

The doctor should be even more wary if the patient can trace his origin back to NW Europe. The screening tests to do first are determination of transferrin saturation and serum ferritin, which can be followed up by genetic testing in cases with high iron stores as appropriate.

Intervention steps may include venesection, diet modification and chelation. The most common treatment for inherited iron overload is regular therapeutic phlebotomies. A regular, weekly phlebotomy (blood letting) of 500ml blood (which is equivalent to about 250mg of iron) may need to be done until the ferritin levels are less than 50 ng/ml and transferrin saturation <30%. After the levels have stabilised, most patients will require maintenance phlebotomies of one unit of blood every two to three months. Blood letting works because the body uses iron in the production of new blood.

Iron chelation is used mostly to treat patients with secondary haemochromatosis, but occasionally it may be useful in patients with one of the primary hereditary forms of the disorder. In patients with far-advanced haemochromatosis, who may have cirrhosis, hypoalbuminemia and congestive heart failure, the need to remove iron is particularly acute but the patient may not be able to tolerate the removal of a large volume of blood over a short period of time. Chelation therapy may also be preferred in patients in whom venous access is very difficult.

There seems to be a misconception that genetic testing in healthy individuals would result in exclusion from life insurance; this does not apply, however, to treatable conditions such as HH identified at an early age if timely preventative measures are implemented. For HH the impact on insurance would depend on the degree of clinical expression at the time of assessment irrespective of a genetic test result. If a family history of HH is present but the applicant has not been tested for this condition, the decision on granting of the policy may be delayed until iron status has been determined, but a DNA test may not be required at this stage. In cases where a genetic predisposition for HH has been identified in the past (due to the presence of two copies of the defective gene) and this finding resulted in precautionary measures being taken to prevent organ damage, the applicant are likely to obtain life insurance at standard rates, provided that no complications occurred over a period of approximately two years prior to submission of the application. In the case of Sanlam and Liberty Life whose medical advisors contributed to an article on genetic testing higher insurance premiums could apply when compliance is not good and where this resulted in development of clinical symptoms related to the genetic defect(s) which have been identified (Kotze et al. 2004).

According to a study by Professor Paul Atkinson of the School of Social Sciences, Cardiff University, published in December 2004 - If someone is told that they are at risk, but have not yet had any symptoms, they are not unduly stressed about their health, provided that they felt they were being looked after. More support for DNA testing without waiting until it is too late to prevent organ damage, comes from a study performed in Australia. Cheek brush samples were taken at the workplace from more than 11000 adults in Australia and 47 people were identified who had two copies of the mutation and about 10% (1 338) who had one. Self-reported tiredness was higher in C282Y++, 19 (83%) of 23 homozygous men and 11 (48%) of 23 homozygous women had raised fasting transferrin saturation. 46/47 have taken steps to treat or prevent iron accumulation .

Interestingly, almost all the participants were pleased they had been tested and no increase in anxiety was found in the people who had both mutations. This finding is in accordance with a Canadian study published in 2001. In fact, it was shown that anxiety decreased significantly in homozygotes and heterozygotes after genetic testing, and remained constant in C282Y mutation-negative cases. The authors concluded that genetic testing for haemochromatosis is well accepted and should not be discouraged on the basis of potential adverse psychosocial effects.

Population screening can be practicable and acceptable: D elatycki et al. Use of community genetic screening to prevent HFE-associated hereditary haemochromatosis. wwwthelancet.com Vol 366 July 23, 2005.]