Phenotypic expression of the HLA linked iron-loading gene in males over the age of 40 years: a population study using serial serum ferritin estimations

Hemochromatosis mutations in the general population: iron overload progression rate

The progression rate of iron overload in hereditary hemochromatosis in individuals in the general population is unknown. We therefore examined in the general population iron overload progression rate in C282Y homozygotes. Using a cohort study of the Danish general population, The Copenhagen City Heart Study, we genotyped 9174 individuals. The 23 C282Y homozygotes identified were matched to 2 subjects each of 5 other HFE genotypes with respect to sex, age, and alcohol consumption. As a function of biologic age, transferrin saturation increased from 50% to 70% from 25 to 85 years of age and from 70% to 80% from 35 to 80 years of age in female and male C282Y homozygotes, respectively. Equivalently, ferritin levels increased from 100 to 500 microg/L and decreased from 800 to 400 microg/L in female and male C282Y homozygotes. As a function of 25 years follow-up irrespective of age, transferrin saturation and ferritin levels increased slightly in male and female C282Y homozygotes. None of the C282Y homozygotes developed clinically overt hemochromatosis. In conclusion, individuals in the general population with C282Y homozygosity at most demonstrate modest increases in transferrin saturation and ferritin levels, and clinically overt hemochromatosis is rare. Therefore, C282Y homozygotes identified during population screening, and not because of clinically overt hemochromatosis, at most need to be screened for manifestations of hemochromatosis every 10 to 20 years.

Frequencies of the hereditary hemochromatosis allele in different populations. Comparison of previous phenotypic methods and novel genotypic methods

AIM

The frequencies of the hereditary hemochromatosis allele were compared for different populations assessed by previous phenotypic methods and the present genotypic methods.

METHODS

From a literature survey, the calculated hemochromatosis allele frequencies from 16 studies using phenotypic biochemical markers (threshold levels for transferrin saturation [range, 46%-70%] and serum ferritin [range, 164-700 microg/L]) were compared with allele frequencies of the Cys282Tyr mutation of the hemochromatosis gene reported in 19 genotypic studies.

RESULTS

Calculated phenotypic allele frequencies are high in Scandinavia: Iceland, 6.1% to 7.4%; Norway, 5.8%; central Sweden, 6.3% to 6.9%; Denmark, 6.1%. Frequencies are similarly high in Wales, Canada, Utah, South Africa, and Australia (range, 5.2%-9.8%). Frequencies are low in Finland (1.9%) and northern Italy (4.5%). Genotypic allele frequencies of the Cys282Tyr mutation are likewise high in Scandinavia. Frequencies are high in the United Kingdom and northern France and low in Finland, central Germany, northern Italy, and Greece. The phenotypic-genotypic ratios of the hemochromatosis homozygosity frequencies for the same geographic area were calculated. A ratio of 1.0 indicates that the 2 methods give similar results. In 3 studies, the ratio was above 1.0, the highest ratio of 1.67 being reported from Italy. In most studies the ratio was slightly below 1.0 (0.71-0.97). The lowest ratio was found in Finland (0.33).

CONCLUSION

In most studies there was good agreement between the hemochromatosis allele frequencies determined by phenotypic and genotypic methods. A high ratio (northern Italy) may indicate that phenotypic selection criteria were too loose and/or that causes of iron overload other than the Cys282Tyr mutation are frequent in the region. A low ratio (in Finland) may indicate phenotypic selection criteria that were too stringent and/or a low penetration rate of the mutation.

Current Clinical Practice: Hereditary Haemochromatosis: Recent Advances in Biology and Management

Hereditary haemochromatosis (HH) is an autosomal recessive disorder leading to excessive absorption of dietary iron. The gene affected in the common variety has recently been identified near the HLA-A locus on chromosome 6 and designated HFE. The HFE mutation, C282Y, responsible for most cases of HH is found in as many as 8-18% of people of European descent; 6-32 per 1000 are therefore homozygous, but only a variable proportion accumulate enough iron to develop organ damage with the associated clinical manifestations. Clinical expression depends on the amount of absorbable iron in the diet, the amount of iron being lost (greater in women through menstruation and pregnancies) and the severity of the genetic defect. The excess iron can be removed by serial phlebotomies. In symptomatic individuals this reverses some of the manifestations and prolongs survival significantly; if treatment is instituted before symptoms appear all manifestations are prevented. The objective must therefore be to identify and treat affected individuals in the presymptomatic stage. In this context, the role of population screening is currently being debated.

Prevalence of hemochromatosis among first-time and repeat blood donors in Norway

BACKGROUND/AIMS

The observed prevalence of hemochromatosis has ranged considerably from 0.05 to 0.37% in studies requiring liver biopsy. We aimed to study the prevalence of genetic hemochromatosis among Norwegian blood donors.

METHODS

We studied 10,552 healthy blood donors (5312 women and 5240 men) using serum ferritin as a screening parameter. If serum ferritin concentration was > or = 100 micrograms/l in women and > or = 200 micrograms/l in men, serum iron and transferrin (measured as total iron binding capacity = TIBC) were measured. Blood donors who repeatedly had a transferrin saturation above 40% and a ferritin concentration above these limits were referred to a hepatologist (H.B.).

RESULTS

Serum ferritin was > or = 100 micrograms/l in 94/5312 (1.8%) women and > or = 200 microliters in 79/5240 (1.5%) men. Of these, 37 persons had a serum ferritin concentration above 100 micrograms/l (females) or above 200 micrograms/l (males) and a transferrin saturation above 40%. Nineteen of them (13 men and 6 women, median age 36 years, range 28-68) were identified as having hemochromatosis on the basis of increased hepatic iron index. Serum ferritin ranged from 111 to 1980 micrograms/l (median 357 micrograms/l and transferrin saturation from 50 to 100% (median 92%), hepatic iron from 48 to 471 mumol/g dry weight (median 118 mumol/g) and hepatic iron index from 1.5 to 12.1 (median 3.0). One person had cirrhosis and none had diabetes. The prevalence of hemochromatosis was significantly higher among first-time blood donors (12 out of 3500 [3.4/1000]) compared with repeat donors (7 out of 7052 [1/1000]), p < 0.005.

CONCLUSIONS

The observed prevalence of hemochromatosis in Norwegian first-time blood donors of 0.34% is comparable to recently observed prevalences in other studies. However, the use of serum ferritin as a first-step screening tool may have failed to detect hemochromatosis in the early stage where iron overload has not yet occurred.

Population screening for haemochromatosis: a unifying analysis of published intervention trials

OBJECTIVES

To examine the efficacy of population screening for haemochromatosis by analysing the screening performance of seven intervention trials, and to compare this with the expected performance derived from family studies.

SETTING

Seven population intervention trials carried out between 1983 and 1995 in Australia, Scandinavia, Iceland, and the United State.

METHODS

Seven of 23 English language trials identified were suitable for the meta-analysis. Transferrin saturation and serum ferritin measurements derived from family studies were used to predict detection and false positive rates for each trial.

RESULTS

The seven trials used various screening and diagnostic criteria. A total of 18,396 men and 12,254 women were screened. Because some cases were not detected by screening, and some screen positive individuals did not complete diagnostic testing, the prevalence of homozygous individuals was underestimated in all the trials. The reported and predicted percentages of screen positive individuals nearly always agreed. The homozygote prevalence was estimated to be 34 men and 40 women per 10,000 (prevalence predicted from family studies is 53 per 10,000). Clinical manifestations were present in 50% of male and 44% of female homozygotes.

CONCLUSIONS

False positive rates, homozygote prevalences, and frequency of clinical manifestations were in general agreement with predictions from family studies. However, incomplete understanding about a number of issues requires that further pilot trials be carried out before screening can be considered part of routine medical practice.

Testing for haemochromatosis in the diabetic clinic

Random serum transferrin saturation (TS) was measured in 1194 patients attending a diabetic clinic. Twenty-one patients had TS > 55% and in three of these patients repeat random TS was < 55%. Seventeen patients were recalled for fasting serum TS and ferritin measurement. Ten patients had fasting TS > 55%. The diagnosis of haemochromatosis was confirmed by liver biopsy in a total of six patients, three of whom were previously unsuspected. Haemochromatosis was the possible diagnosis in a further four patients. Family studies using HLA typing confirmed haemochromatosis in four family members, three of whom were asymptomatic. We conclude that measurement of TS is a simple and effective method of finding cases of haemochromatosis in the diabetic clinic.

Screening blood donors for hereditary hemochromatosis: decision analysis model based on a 30-year database

BACKGROUND & AIMS

The high prevalence, morbidity, premature death, and benefit of early diagnosis and treatment make hemochromatosis a prime target for screening in the white population. Decision analysis techniques were used to compare the outcome, utility, and incremental cost savings of a plan to screen voluntary blood donors for hemochromatosis.

METHODS

The screening strategy includes sequential testing of serum unsaturated iron-binding capacity, serum transferrin saturation, serum ferritin, and either hepatic iron index or venesections to measure exchangeable body iron. Estimates of prevalence, asymptomatic intervals, probabilities of life-threatening clinical complications, symptom-specific life expectancy, and sensitivity and specificity of screening tests are based on our database of 170 hemochromatosis homozygotes and the published literature.

RESULTS

The screening strategy led to an incremental increase in utility of 0.84 quality-adjusted life days with an incremental cost savings of $3.19 per blood donor screened. When the potential of identifying asymptomatic homozygous siblings was included, these values increased to 1.18 quality-adjusted life days and $12.57 per person screened. Screening remained a dominant strategy given a prevalence of hemochromatosis of > 0.0026 or an initial screening test cost of < $8.

CONCLUSIONS

Screening blood donors for hemochromatosis has the potential to improve overall societal health status and decrease third-party payer health care costs over the long-term.

Clinical spectrum and management of haemochromatosis

Haemochromatosis is one of the most common inborn errors of metabolism. In prospective epidemiological studies the frequency of haemochromatosis is 0.0037 (76/20333 subjects) for homozygotes which corresponds to a gene frequency of 0.061 and a frequency of heterozygotes of 0.115. Abnormality in liver function tests, weakness and lethargy, skin hyperpigmentation, diabetes mellitus, arthralgia, impotence and ECG abnormalities are the most frequent findings and symptoms at diagnosis. In recent years about 50% of patients were detected without having liver cirrhosis and 20% of patients did not have any symptoms and pathology except iron overload. Survival analyses in long-term studies showed that in the absence of cirrhosis and diabetes, iron removal by phlebotomy therapy prevents further tissue damage and guarantees a normal life expectancy. Patients with massive and long-lasting iron overload had a worse prognosis than those with less severe iron excess. Iron removal in general ameliorated liver disease, weakness and cardiac abnormalities, and also prevented the progression of endocrine alterations. Therapy, however, did not influence insulin-dependent diabetes. Most deaths in patients with hereditary haemochromatosis were caused by liver cancers which often occurred many years after complete iron removal. In patients with haemochromatosis, liver cirrhosis, cardiomyopathy, and diabetes mellitus are also significantly more frequent causes of deaths when compared with the general population. Further strategies have to evaluate the design of screening programmes in order to diagnose more patients in the precirrhotic and asymptomatic stage.

Management of hereditary hemochromatosis

Hereditary hemochromatosis is a common disorder of iron metabolism with a prevalence as high as 8 per 1000. Affected individuals absorb excessive amounts of dietary iron and over time, tissue iron deposition results in skin discoloration, arthropathy, hepatic cirrhosis, heart failure, diabetes mellitus and impotence. Early diagnosis and institution of phlebotomy treatments will prevent these manifestations and normalize life expectancy. Once organ damage is established many of the manifestations are irreversible. Since the early manifestations of the disease are subtle, a case can be made for routine screening. This conclusion is supported by cost-effectiveness analysis based on available data. A reasonable screening strategy would start with a serum transferrin saturation. A value > or = 55% should trigger a repeat transferrin saturation in a fasting state and a serum ferritin level. If both these tests are abnormal, a liver biopsy with quantitative iron determination is the currently accepted confirmatory test.

Screening for hemochromatosis: a cost-effectiveness study based on 12,258 patients

BACKGROUND/AIMS

Current emphasis in hemochromatosis has focused on early detection and treatment to prevent permanent liver damage and hepatocellular carcinoma. Thus far, only normal population and high-risk groups have been screened but not patients seeking medical care.

METHODS

Serum iron levels were determined in consecutive fasting blood samples collected in the morning from 12,258 Mayo Clinic patients.

RESULTS

One hundred twenty-seven patients had an initial serum iron concentration > or = 180 micrograms/dL. Eight patients (age, 38-71 years; 7 men and 1 woman) had transferrin saturation > or = 62% (range, 84-99) and serum ferritin value > or = 400 micrograms/L (range, 457-4004) with no other explanation for the abnormal iron test results. Three patients (2 male and 1 female) had markedly elevated hepatic iron concentration (range, 11,080-29,719 micrograms/g dry wt) and hepatic iron index (range, 2.9-8.4) indicative of homozygous hemochromatosis. One patient who refused liver biopsy had 7 g of iron removed by phlebotomy and is likely homozygous. Two patients had hepatic iron indices < 1.5 and are probably heterozygous. The genetic status of 1 patient is indeterminate, and 1 patient with normal hepatic iron concentration and hepatic iron index had chronic active hepatitis. None had cirrhosis, diabetes, or cardiomyopathy. No patients with hemochromatosis would have been detected without this study.

CONCLUSIONS

The yield in this study, 0.33 cases of 1000 screened, is approximately one tenth of the predicted homozygote frequency by recent estimates. Even at this yield, screening appears cost-effective.

Serum transferrin receptor in hereditary hemochromatosis and African siderosis

The present investigation evaluated the serum transferrin receptor concentration in subjects with nontransfusional iron overload who were identified in two separate studies on the basis of a serum ferritin level above 400 micrograms/L. Subjects with preclinical hereditary hemochromatosis were evaluated in the first study and those with the African form of iron overload in the second. In the first study, hereditary hemochromatosis was identified in 14 white men on the basis of a persistent elevation in transferrin saturation above 55%. The serum receptor concentration was elevated above the upper cut-off of 8.5 mg/L in two of the subjects, but the mean receptor of 6.1 +/- 1.4 mg/L (mean +/- 2 SE) did not differ significantly from the normal mean for this assay of 5.6 +/- 0.3 mg/L. In the same study, 60 control subjects with secondary iron overload were identified on the basis of a serum ferritin persistently above 400 micrograms/L, with a normal serum C-reactive protein concentration but with a transferrin saturation < 55%. Three of these subjects had an elevated serum receptor concentration but the mean value of 5.5 +/- 0.4 mg/L did not differ from normals nor from subjects with hemochromatosis. In the second study, 49 black Africans with iron overload were divided into those with or without an elevated transferrin saturation. The mean serum receptor concentration of 5.0 +/- 0.8 mg/L and 4.5 +/- 0.4 mg/L, respectively, did not differ statistically. It was concluded that there is no evidence of generalized dysregulation of the transferrin receptor in hemochromatosis or African siderosis.

Epidemiology, clinical spectrum and prognosis of hemochromatosis

EPIDEMIOLOGY

Eleven prospective epidemiological studies from various countries have as yet evaluated the gene prevalence of HLA-linked hemochromatosis. The estimated frequency ranged from 0.027-0.107, the frequency of homozygotes from 0.00074-0.0116, and the frequency of heterozygotes from 0.052-0.191. In a meta-analysis of the eleven surveys the frequency is 0.0016 (106/64758 subjects) for homozygotes which corresponds to a gene frequency of 0.041 and a frequency of heterozygotes of 0.078. Further analyses showed that some of these studies have probably underestimated the prevalence which in reality is probably two- to threefold higher than estimated by the meta-analysis.

CLINICAL SPECTRUM

In the total group of 251 patients diagnosed with hemochromatosis in the University of Düsseldorf from 1959-1992, abnormality in liver function tests (75%), weakness and lethargy (74%), skin hyperpigmentation (70%), diabetes mellitus (48%), arthralgia (44%), impotence (45% in males), and ECG abnormalities (31%) were the most frequent findings and symptoms at diagnosis. In recent years about 50% of patients were detected without having liver cirrhosis and 20% of patients did not have any symptoms and pathology except iron overload.

PROGNOSIS

Survival analysis in the 251 patients showed that in the absence of cirrhosis and diabetes iron removal by phlebotomy therapy prevents further tissue damage and guarantees a normal life expectancy. Sex and presence of arthropathy did not predict prognosis. However, patients with massive and long-lasting iron overload had a worse prognosis than patients with less severe iron excess. Iron removal in general ameliorated liver disease, weakness and cardiac abnormalities, and also prevented the progression of endocrine alterations. Therapy, however, did not influence arthropathy which even got worse in several patients. Iron removal also failed to reverse insulin-dependent diabetes. During a mean followup of 13.4 years 69 deaths occurred in the 251 patients. In 19 patients death was due to liver cancer, in 14 due to liver cirrhosis, in 5 due to cardiomyopathy, and in 3 due to diabetes mellitus (all causes significantly more frequent than expected for the general population). The other causes of death were as frequent as expected including extrahepatic malignancies. All liver cancers were seen in cirrhotic livers, but often occurred many years or even decades after complete iron removal. Further strategies have to evaluate the design of screening programs in order to diagnose more patients in the precirrhotic and asymptomatic stage.

A prevalence and fertility study of haemochromatosis in Saguenay-Lac-Saint-Jean

The prevalence of hereditary haemochromatosis (HH) in Saguenay-Lac-St-Jean (SLSJ), a geographically isolated region of northeastern Québec, was estimated at 0.014; the heterozygote frequency was 0.21. These are among the highest frequencies found thus far in white populations. The fertility study completed in SLSJ showed that carriers of the HH gene tended to have more children than non-carriers. However, since these differences were not statistically significant, there appears to be no basis on which to accept that HH heterozygotes are at a selective advantage. Therefore, genetic drift cannot be excluded.

Serum ferritin, blood donation, iron stores and haemochromatosis

Serum iron and ferritin concentrations were measured in 1,532 regular blood donors from South Wales who were undergoing HLA typing prior to registration on the British Bone Marrow and Platelet Donor Panel. Serum transferrin concentrations were determined for donors with serum iron concentrations > 24 mumol/l. There were 25 donors with transferrin saturations > 50% and 11 with transferrin saturations > 60%. There were five donors with serum ferritin concentrations > 200 micrograms/l (women) or > 300 micrograms/l (men). Two of the male donors had transferrin saturations > 50% and serum ferritin > 300 micrograms/l on repeat blood samples and are being treated by venesection. Donors with HLA-A3 did not differ from those without A3 in serum iron or ferritin concentrations. Even in the group of donors who were apparently homozygous for A3 there were neither abnormal serum iron nor ferritin concentrations. Although it is well established that measurements of transferrin saturation are required to detect homozygous haemochromatosis (HFE) in its earlier stages, the number of 'false-positive' results is likely to be unacceptably high for screening blood donors. Serum ferritin assays should identify donors with HFE and iron overload before the onset of liver damage. With two million regular donors and 300,000 new donors each year, a significant proportion of the U.K. population will be screened within 10 years. The assay of serum ferritin identifies donors with low levels of storage iron who are at risk of developing iron-deficiency anaemia. Furthermore, donation frequency may be increased for those donors with higher ferritin concentrations when blood supplies are low.