Transferrin receptor-2 (TFR2) mutation Y250X in Alabama Caucasian and African American subjects with and without primary iron overload

Analysis of HFE and non-HFE gene mutations in Brazilian patients with hemochromatosis

BACKGROUND

Approximately one-half of Brazilian patients with hereditary hemochromatosis (HH) are neither homozygous for the C282Y mutation nor compound heterozygous for the H63D and C282Y mutations that are associated with HH in Caucasians. Other mutations have been described in the HFE gene as well as in genes involved in iron metabolism, such as transferrin receptor 2 (TfR2) and ferroportin 1 (SCL40A1).

AIMS

To evaluate the role of HFE, TfR2 and SCL40A1 mutations in Brazilian subjects with HH.

PATIENTS AND METHODS

Nineteen male subjects (median age 42 [range: 20-72] years) with HH were evaluated using the Haemochromatosis StripAssay A. This assay is capable of detecting twelve HFE mutations, which are V53M, V59M, H63D, H63H, S65C, Q127H, P160delC, E168Q, E168X, W169X, C282Y and Q283, four TfR2 mutations, which are E60X, M172K, Y250X, AVAQ594-597del, and two SCL40A1 mutations, which are N144H and V162del.

RESULTS

In our cohort, nine (47%) patients were homozygous for the C282Y mutation, two (11%) were heterozygous for the H63D mutation, and one each (5%) was either heterozygous for C282Y or compound heterozygous for C282Y and H63D. No other mutations in the HFE, TfR2 or SCL40A1 genes were observed in the studied patients.

CONCLUSIONS

One-third of Brazilian subjects with the classical phenotype of HH do not carry HFE or other mutations that are currently associated with the disease in Caucasians. This observation suggests a role for other yet unknown mutations in the aforementioned genes or in other genes involved in iron homeostasis in the pathogenesis of HH in Brazil.

Early age-of-onset iron overload and homozygosity for the novel hemojuvelin mutation HJV R54X (exon 3; c.160A-->T) in an African American male of West Indies descent

An African American male of West Indies descent was diagnosed to have elevated transferrin saturation, hyperferritinemia, severe iron deposition in hepatocytes, and hepatic cirrhosis at age 4. He was treated with serial phlebotomy to maintain a normal serum ferritin concentration thereafter. We evaluated him at age 23 and confirmed that he had normal serum ferritin levels, severe iron deposition in hepatocytes, hepatic cirrhosis, and portal hypertension. He did not have endocrinopathy, cardiomyopathy, or arthropathy. He was homozygous for the novel hemojuvelin (HJV) premature stop-codon mutation R54X (exon 3; c.160A-->T). He did not have either HFE C282Y, H63D, or S65C, or deleterious coding region mutations of SLC40A1, TFR2, or HAMP. His erythrocyte measures and hemoglobin electrophoresis were consistent with alpha-thalassemia trait. We conclude that homozygosity for HJV R54X accounts for his severe, early age-of-onset hemochromatosis; his phenotype was probably modified by serial phlebotomy therapy.

Of mice and men: genetic determinants of iron status

Fe homeostasis is maintained by regulation of Fe absorption to balance largely unregulated body Fe losses. The majority of human subjects maintain relatively constant Fe stores; however, Fe deficiency and Fe overload are common conditions. Fe overload is frequently associated with mutations in genes of Fe metabolism. The present paper summarises present knowledge of these mutations as well as indicating other genes that animal studies have implicated as candidates for influencing body Fe stores.

Transferrin receptor 2 is emerging as a major player in the control of iron metabolism

Our knowledge of mammalian iron metabolism has advanced dramatically over recent years. Iron is an essential element for virtually all living organisms. Its intestinal absorption and accurate cellular regulation is strictly required to ensure the coordinated synthesis of the numerous iron-containing proteins involved in key metabolic processes, while avoiding the uptake of excess iron that can lead to organ damage. A range of different proteins exist to ensure this fine control within the various tissues of the body. Among these proteins, transferrin receptor (TFR2) seems to play a key role in the regulation of iron homeostasis. Disabling mutations in TFR2 are responsible for type 3 hereditary hemochromatosis (Type 3 HH). This review describes the biological properties of this membrane receptor, with a particular emphasis paid to the structure, function and cellular localization. Although much information has been garnered on TFR2, further efforts are needed to elucidate its function in the context of the iron regulatory network.

Hemochromatosis: genetics and pathophysiology

A number of genetic disorders can result in the accumulation of excess iron in the body. These causes of hereditary hemochromatosis include defects in genes encoding HFE, transferrin receptor 2, ferroportin, hepcidin, and hemojuvelin. Hepcidin, with its cognate receptor, ferroportin, has emerged as a central regulator of iron homeostasis; all of the known causes of hemochromatosis appear to prevent this system from functioning normally. The most common form of primary hemochromatosis is that caused by C282Y mutation of the HFE gene. This mutation is most prevalent among Northern Europeans. Although the frequency of the homozygous genotype is approximately 5 per 1000, the disease itself is quite rare because the clinical penetrance of the genotype is very low.

Initial screening transferrin saturation values, serum ferritin concentrations, and HFE genotypes in whites and blacks in the Hemochromatosis and Iron Overload Screening Study

We compared initial screening data of 44,082 white and 27,124 black Hemochromatosis and Iron Overload Screening (HEIRS) Study participants. Each underwent serum transferrin saturation (TfSat) and ferritin (SF) measurements without regard to fasting, and HFE C282Y and H63D genotyping. Elevated measurements were defined as: TfSat more than 50% (men), more than 45% (women); and SF more than 300 ng/ml (men), more than 200 ng/ml (women). Mean TfSat and percentages of participants with elevated TfSat were significantly greater in whites than in blacks. Mean SF and percentages of participants with elevated SF were significantly greater in blacks than in whites. TfSat and SF varied by gender and age in whites and blacks. Prevalences of genotypes that included either C282Y or H63D were significantly greater in whites than in blacks. The prevalence of elevated TfSat and SF plus genotypes C282Y/C282Y, C282Y/H63D, or H63D/H63D was 0.006 in whites and 0.0003 in blacks. Among whites with HFE C282Y homozygosity, 76.8% of men and 46.9% of women had elevated TfSat and SF values. Three black participants had HFE C282Y homozygosity; one had elevated TfSat and SF values. Possible explanations for differences in TfSat and SF in whites and blacks and pertinence to the detection of hemochromatosis, iron overload, and other disorders with similar phenotypes are discussed.

Genetic background of primary iron overload syndromes in Japan

The different prevalences of iron overload syndromes between Caucasians and Asians may be accounted for by the differences in genetic background. The major mutation of hemochromatosis in Celtic ancestry, C282Y of HFE, was reported in a Japanese patient. Five patients of 3 families with the hepatic transferrin receptor gene (TFR2)-linked hemochromatosis were found in different areas of Japan, suggesting that TFR2 is a major gene in Japanese people. Three patients with mutations in the hemojuvelin gene, HJV, showed also middle-age-onset hemochromatosis. A heterozygous mutation in the H ferritin gene, FTH1, was found in a family of 3 affected patients. Another autosomal dominant SLC40A1-linked hyperferritinemia (ferroportin disease) was found in 3 patients of 2 families. Two patients with hemochromatosis were free from any mutations in the genes investigated. In conclusion, the genetic backgrounds of Japanese patients with primary iron overload syndromes were partially clarified, showing some phenotype-genotype correlations.

The evaluation of hyperferritinemia: an updated strategy based on advances in detecting genetic abnormalities

The number of new genes implicated in iron metabolism has dramatically increased during the last few years. Alterations of these genes may cause hyperferritinemia associated or not with iron overload. Correct assignment of the specific disorder of iron metabolism requires the identification of the causative gene mutation. Here, we propose a rational strategy that allows targeting the gene(s) to be screened for a diagnostic purpose. This strategy relies on the age of onset of the disease, the type of clinical symptoms, the biochemical profile (elevated or normal serum transferrin saturation (TfSat)), the presence or not of visceral iron excess, and the mode of inheritance (autosomal recessive or dominant). Then, two main entities can be differentiated: genetic (adult or juvenile) hemochromatosis characterized by elevated TfSat, and hereditary hyperferritinemias where TfSat is normal (or only slightly modified). Adult genetic hemochromatosis (GH) is related mainly to mutations of the HFE gene, and exceptionally to mutations of the TFR2 gene. Juvenile GH is a rare condition related principally to mutations of the HJV gene coding for hemojuvelin, and rarely to mutations of the HAMP gene coding for hepcidin. Hereditary hyperferritinemias are linked to mutations of three genes: the L-ferritin gene responsible for the hereditary hyperferritinemia cataract syndrome (without iron overload), the ferroportin gene leading to a dominant form of iron overload, and the ceruloplasmin (CP) gene corresponding to an iron overload syndrome with neurological symptoms. The proposed strategic approach may change with the identification of other genes involved in iron metabolism.

Common heterozygous hemochromatosis gene mutations are risk factors for inflammation and fibrosis in chronic hepatitis C

BACKGROUND

Chronic hepatitis C is frequently associated with increased hepatic iron stores. It remains controversial whether heterozygous mutations of hemochromatosis genes affect fibrosis progression. Therefore our aim was to assess associations between HFE mutations and hepatic inflammation and stage of fibrosis in German hepatitis C patients.

METHODS

Liver biopsies from 166 patients were scored for inflammatory activity (A0-4) and hepatic fibrosis (F0-4). Gene mutations were determined by LightCycler, restriction fragment length polymorphism analysis, or direct sequencing.

RESULTS

The frequencies of common HFE mutations C282Y and H63D are 4.2% and 21.3%, whereas the recently described S65C substitution and the Y250X mutation in the transferrin receptor 2 gene are very rare. In regression analysis, heterozygous carriers of C282Y or H63D mutations display significantly (P < 0.05) higher inflammatory activities and more advanced fibrosis than patients without mutations. For C282Y heterozygous patients, the odds ratios for marked inflammatory activity (A2-4) and advanced liver fibrosis or cirrhosis (F2-4) are 4.9 and 4.6, respectively, compared with patients carrying homozygous wild-type alleles. C282Y mutations are associated with significantly (P < 0.05) increased serum iron and aminotransferase levels, whereas H63D heterozygotes display higher transferrin saturation, serum iron, and ferritin concentrations compared to wild-type (P < 0.01).

CONCLUSIONS

Common heterozygous hemochromatosis mutations are associated with higher grades of inflammation and more severe hepatic fibrosis. Our findings support a role of HFE mutations as primary risk factors for fibrogenesis and disease progression in chronic hepatitis C.

Genotypic and phenotypic heterogeneity of African Americans with primary iron overload

Primary iron overload may be relatively common in African Americans, but its cause is incompletely understood. Thus, we evaluated genotype and phenotype characteristics of unselected African American index patients with primary iron overload who reside in central Alabama. All had hepatic iron concentration > or =30 micromol/g dry wt or > or =2.0 g of iron mobilized by phlebotomy to achieve iron depletion. Genotype analyses were performed in African American control subjects from the same region. There were 23 patients (19 men, 4 women); mean age at diagnosis was 52 +/- 12 years (1 SD) (range 32-69 years). Nine (39.1%) reported that they consumed > or =45 g of ethanol daily; five had chronic hepatitis C. Eight had some form of hemoglobinopathy or thalassemia. Mean serum transferrin saturation was 56 +/- 28% (range 15-100%). The geometric mean serum ferritin at diagnosis was 1076 ng/mL [95% confidence interval 297-3473 ng/mL]. Increased stainable liver iron was observed in hepatocytes only in 4 patients, in macrophages only in 8 patients, and in hepatocytes and macrophages in 8 patients. The mean quantity of iron mobilized by phlebotomy (corrected for iron absorbed during treatment) was 5.3 +/- 2.0 g (range 4.0-8.4 g). Iron removed by phlebotomy was greater in patients with hemoglobinopathy or thalassemia than in those without these forms of anemia (6.6 +/- 1.3 g vs 3.9 +/- 1.6 g, respectively; P = 0.0144). Daily consumption of > or =45 g of ethanol or chronic hepatitis C was not associated with an increased or decreased amount of phlebotomy-mobilized iron, on the average. The percentage of index patients positive for HFE C282Y was greater than that of controls (P = 0.0058). The respective percentages of phenotype positivity for HFE H63D, D6S105(8), and HLA-A*03 were similar in patients and controls. HFE S65C, I105T, and G93R were not detected in index or control subjects. Two of 13 patients were heterozygous for the ferroportin allele nt 744 G-->T (Q248H), although the phenotype frequency of this allele was similar in patients and 39 controls. Synonymous ferroportin alleles were also detected in some patients. The ceruloplasmin mutation nt 1099C-->T (exon 6; Arg367Cys) was detected in 1 of 2 patients tested. Abnormal alleles of beta-2 microglobulin, Nramp2, TFR2, hepcidin, or IRP2 alleles were not detected in either of the 2 patients so tested. We conclude that primary iron overload in African Americans is not the result of the mutation of a single gene. HFE C282Y, ferroportin 744 G-->T, and common forms of heritable anemia appear to account for increased iron absorption or retention in some patients.

Early onset hereditary hemochromatosis resulting from a novel TFR2 gene nonsense mutation (R105X) in two siblings of north French descent

The molecular basis of hereditary hemochromatosis (HH) is more complex than previously expected. More than 80% of hemochromatosis probands of Northern European descent are homozygous for the C282Y HFE gene mutation. However, five novel non-related-HFE HH forms have now been identified. The transferrin receptor(TFR2)-linked form is inherited in an autosomal recessive pattern and is considered to be an adult-onset syndrome. Until now, it has been associated with five mutations that have only been detected in Japanese and southern European patients. Here, we report the identification of a novel TFR2 nonsense mutation in two related French adolescents. We discuss the phenotype of this sibling pair from precedent biological and clinical findings as well as the expected role of TFR2 in iron homeostasis. Finally, we suggest that iron overload phenotypes associated with mutations in TFR2 may be intermediate between those related to mutations in HFE and those related to mutations in juvenile hemochromatosis genes.

Can defects in transferrin receptor 2 and hereditary hemochromatosis genes account for iron overload in HbH disease?

Iron overload was found to be the major cause of disability in Chinese HbH disease patients although they were not on regular blood transfusion. The transferrin receptor 2 (TFR2) and hereditary hemochromatosis (HFE) genes were examined to see if inheritance of these gene defects may be a possible cause of iron overload in 45 HbH patients. A novel intronic (IVS6 (+6) T-->A) mutation of the TFR2 gene was identified in one patient, and six others were found to carry a known missense mutation (exon 5, I238M) that was also present in one normal control subject. One HbH patient and one normal control carried the H63D mutation of the HFE gene. Since only eight out of 45 iron-overloaded HbH patients carry a defect in the TFR2 or HFE gene in the heterozygote state and their iron loading status was comparable to the matched controls without such defects, it would appear that the accumulation of excess iron in HbH disease is more likely a result of increase dietary absorption secondary to ineffective erythropoiesis.

Hemochromatosis due to mutations in transferrin receptor 2

A rare recessive disorder which leads to iron overload and severe clinical complications similar to those reported in HFE-related hemochromatosis has been delineated and sometimes called hemochromatosis type 3. The gene responsible is Transferrin Receptor 2 (TFR2), which maps to chromosome 7q22. The TFR2 gene presents a significative homology to transferrin receptor (TFRC) gene, encodes for a transmembrane protein with a large extracellular domain, is able to bind transferrin, even if with lower affinity than TFRC. The TFR2 function is still unclear. The transcript does not contain IRE elements and is not modified by the cellular iron status. At variance with TFRC, interactions between TFR2 and HFE do not occur, at least in their soluble forms. TFR2 is spliced in two alternative forms, alfa and beta. The alfa form is strongly expressed in the liver. The beta form, codified from a start site in exon 4 of the alpha, has a low and ubiquitous expression. Using anti-TFR2 monoclonal antibodies we have confirmed expression of the protein in the liver but also in duodenal epithelial cells, and studied the protein functional behaviour in cell lines, in response to iron addition, iron deprivation and olo-transferrin exposure. Our results suggest a regulatory role of TFR2 in iron metabolism. Five TFR2 homozygous mutations have been documented in HFE3 patients: a nonsense mutation (Y250X); a C insertion that causes a frameshift and a premature stop codon (E60X); a missense mutation (M172K); a 12 basepair deletion in exon 16, that causes 4 aminoacid loss (AVAQ 594-597del) in the extracellular domain of TFR2; a missense mutation in exon 17 (Q690P). The mutation analysis supports the hypothesis that all are private mutations. The pathogenetic role of TFR2 in hemochromatosis has been recently further demonstrated through the targeted expression of the Y250X human mutation in mice, which develop sings of iron overload identical to the human disease. Although the rarity of TFR2 mutations limits their usefulness in diagnostic/screening programs, their study can contribute to a better understanding of the protein function.

African iron overload

Iron overload is common in rural sub-Saharan African populations that have the custom of drinking a traditional fermented beverage with high iron content. As with both excessive alcohol exposure and HFE hemochromatosis, hepatic portal fibrosis and micronodular cirrhosis are prominent sequelae of African iron overload. Two observations are therefore important in characterizing iron overload in Africa. First, the hepatic iron concentrations associated with African iron overload often far exceed those seen in alcoholic liver disease and histologic changes of alcohol effect are almost always absent. Second, the pattern of iron accumulation in African dietary iron is prominent in both macrophages and hepatic parenchymal cells; this pattern is in contrast to HFE homochromatosis, which is marked by predominantly parenchymal iron-loading. For a long time, it was thought that African iron overload was purely dietary in nature, that increased iron and alcohol in the diet could fully explain markedly elevated tissue iron levels sometimes seen with this condition. Recent studies of pedigrees suggest that, in addition to high dietary iron content, a genetic defect may also be implicated in iron overload in Africans. These studies indicate that the possible defect is different from mutations in the HFE gene frequently found in Caucasians with iron overload, but the putative gene has not been identified. Recent studies also indicate that non-HFE iron overload occurs in African-Americans, but the prevalence and possible genetic basis is yet to be determined.

Targeted mutagenesis of the murine transferrin receptor-2 gene produces hemochromatosis

Hereditary hemochromatosis (HH) is a common genetic disorder characterized by excess absorption of dietary iron and progressive iron deposition in several tissues, particularly liver. The vast majority of individuals with HH are homozygous for mutations in the HFE gene. Recently a second transferrin receptor (TFR2) was discovered, and a previously uncharacterized type of hemochromatosis (HH type 3) was identified in humans carrying mutations in the TFR2 gene. To characterize the role for TFR2 in iron homeostasis, we generated mice in which a premature stop codon (Y245X) was introduced by targeted mutagenesis in the murine Tfr2 coding sequence. This mutation is orthologous to the Y250X mutation identified in some patients with HH type 3. The homozygous Tfr2(Y245X) mutant mice showed profound abnormalities in parameters of iron homeostasis. Even on a standard diet, hepatic iron concentration was several-fold higher in the homozygous Tfr2(Y245X) mutant mice than in wild-type littermates by 4 weeks of age. The iron deposition in the mutant mice was predominantly hepatocellular and periportal. The mean splenic iron concentration in the homozygous Tfr2(Y245X) mutant mice was significantly less than that observed in the wild-type mice. The homozygous Tfr2(Y245X) mutant mice also demonstrated elevated transferrin saturations. There were no significant differences in parameters of erythrocyte production including hemoglobin levels, hematocrits, erythrocyte indices, and reticulocyte counts. Heterozygous Tfr2(Y245X) mice did not differ in any measured parameter from wild-type mice. This study confirms the important role for TFR2 in iron homeostasis and provides a tool for investigating the excess iron absorption and abnormal iron distribution in iron-overload disorders.

A primer for predicting risk of disease in HFE-linked hemochromatosis

Since the discovery of the hemochromatosis gene (HFE) in 1996, there has been increasing interest in diagnostic testing for the C282Y and H63D mutations. The high frequency of these two alleles and their incomplete penetrance in homozygotes and compound heterozygotes make genetic counseling for hemochromatosis different from some other autosomal recessive conditions in that parents and children may also be at risk for iron overload, while homozygotes may remain asymptomatic. We provide a guideline for genetic counseling in HFE-linked hemochromatosis based on the genetic probability of inheriting HFE mutations and known information about expression of iron overload in various HFE genotypes. Genetic probabilities were based on allele frequencies derived from large population studies and Hardy-Weinberg equilibrium estimates. Expression of iron overload in those of various genotypes was based on available estimates of serum ferritin from population screening studies. Estimates for the likelihood of clinical iron overload requiring follow-up screening or treatment are provided by gender and genotype. The probability of inheriting HFE mutations and developing iron overload can be estimated in family members of a proband with HFE mutations. Many C282Y homozygotes will not have clinical iron overload. The risk is highest in men and their C282Y homozygous brothers and significantly lower in homozygous women. Iron overload is uncommon in compound heterozygotes and H63D homozygotes.

Clinical and pathologic findings in hemochromatosis type 3 due to a novel mutation in transferrin receptor 2 gene

BACKGROUND & AIMS

Although most patients with hereditary hemochromatosis are homozygous for a single mutation of the HFE gene on chromosome 6p, accumulating evidence indicates that the disease is genetically heterogeneous. Type 3 hemochromatosis, recently described in 4 families, is linked to mutations of the gene encoding transferrin receptor 2 on chromosome 7q22. Here we report data from a family carrying a new mutation of the transferrin receptor 2 gene.

METHODS

Detailed clinical and histopathologic documentation was available for most family members. The entire coding sequence and exon/intron boundaries of the transferrin receptor 2 gene were analyzed by direct sequencing.

RESULTS

A 12-nucleotide deletion in exon 16, causing the loss of 4 amino acids (AVAQ 594-597 del), was detected at the homozygous state in the 3 patients with histologically proven iron overload. The deletion segregated with the disease within the family and was not found in 100 healthy controls. Some clinical and pathologic characteristics, such as low penetrance in the premenopausal woman, and early iron deposition in periportal hepatocytes resembled those of classic, HFE-related hemochromatosis.

CONCLUSIONS

Our data support the role of the transferrin receptor 2 gene in hemochromatosis type 3 as well as its critical involvement in the maintenance of iron homeostasis in humans.

Discrepancies between genotype and phenotype in hematology: an important frontier

An African American male infant with sickle cell disease has a devastating stroke; an African American soldier is surprised when he is informed that he has sickle cell disease. They are both homozygous for the same mutation. An Ashkenazi Jewish woman with Gaucher disease has a huge spleen and severe thrombocytopenia; her older brother, homozygous for the same 1226G glucocerebrosidase mutation, is found on routine examination to have a barely palpable spleen tip. The fact that clinical manifestations of genetic diseases can vary widely among patients has been recognized for many decades. In the past, however, it could often be attributed to the pleomorphic nature of mutations of the same gene: the patient with severe disease, it was averred, must have a different mutation than the one with mild disease. Even before a precise definition of mutations could be achieved at the DNA level, such an explanation did not serve to clarify the differences that existed between siblings with the same autosomal recessive disease. Such siblings must surely be carrying the same 2 disease-producing alleles. With the advent of sequence analysis of genes, the great extent of phenotype variation in patients with the same genotype has come to be more fully appreciated, but understanding of why it occurs continues to be meager. It is the purpose of this review to explore some of the variations in phenotype seen by hematologists in patients with identical mutations, to indicate where some progress has been made, and to suggest how understanding in this important area may be expanded.

A study of genes that may modulate the expression of hereditary hemochromatosis: transferrin receptor-1, ferroportin, ceruloplasmin, ferritin light and heavy chains, iron regulatory proteins (IRP)-1 and -2, and hepcidin

We have examined transferrin receptor-1, ferroportin, ceruloplasmin, ferritin light and heavy chains, iron regulatory proteins (IRP)-1 and -2, and hepcidin for mutations that might modulate the iron burden of individuals harboring the common mutant hemochromatosis HFE genotype C282Y/C282Y or cause hemochromatosis independent of mutations in the HFE gene. In a group of white, Asian, and African-American normal and iron-overloaded individuals, the coding and flanking regions of these genes were completely sequenced. Numerous coding region and promoter polymorphisms were detected. These were further examined for association with differences in iron accumulation as measured by plasma transferrin saturation and ferritin levels, but no such association could be documented.

Inheritance of two HFE mutations in African Americans: cases with hemochromatosis phenotypes and estimates of hemochromatosis phenotype frequency

PURPOSE

Two unrelated African Americans had hemochromatosis phenotypes and genotypes. We sought to identify origins of their HFE mutations and estimate frequencies of similar cases.

METHODS

HFE and HLA genotyping were performed in index cases and family members. HFE genotypes of 1,373 African American controls in five regions were tabulated.

RESULTS

Index cases had C282Y/C282Y and C282Y/H63D, respectively; each corresponding Ch6p was likely of Caucasian origin. In controls, frequencies of hemochromatosis-associated genotypes were as follows: C282Y/C282Y, 0.00011; C282Y/H63D, 0.00067; and H63D/H63D, 0.00101.

CONCLUSIONS

Penetrance-adjusted estimates indicate that approximately 9 African Americans per 100,000 have a hemochromatosis phenotype and two common HFE mutations. Hemochromatosis-associated genotype frequencies varied 11.7-fold across regions.