Seeking candidate mutations that affect iron homeostasis

Gnpat does not play an essential role in systemic iron homeostasis in murine model

The GNPAT variant rs11558492 (p.D519G) was identified as a novel genetic factor that modifies the iron‐overload phenotype in homozygous carriers of the HFE p.C282Y variant. However, the reported effects of the GNPAT p.D519G variant vary among study populations. Here, we investigated the role of GNPAT in iron metabolism using Gnpat‐knockout (Gnpat^−/−), Gnpat/Hfe double‐knockout (Gnpat^−/−Hfe^−/− or DKO) mice and hepatocyte‐specific Gnpat‐knockout mice (Gnpat^fl/fl;Alb‐Cre). Our analysis revealed no significant difference between wild‐type (Gnpat^+/+) and Gnpat^−/− mice, between Hfe^−/− and DKO mice, or between Gnpat^fl/fl and Gnpat^fl/fl;Alb‐Cre with respect to serum iron and tissue iron. In addition, the expression of hepcidin was not affected by deleting Gnpat expression in the presence or absence of Hfe. Feeding Gnpat^−/− and DKO mice a high‐iron diet had no effect on tissue iron levels compared with wild‐type and Hfe^−/− mice, respectively. Gnpat knockdown in primary hepatocytes from wild‐type or Hfe^−/− mice did not alter hepcidin expression, but it repressed BMP6‐induced hepcidin expression. Taken together, these results support the hypothesis that deleting Gnpat expression has no effect on either systemic iron metabolism or the iron‐overload phenotype that develops in Hfe^−/− mice, suggesting that GNPAT does not directly mediate iron homeostasis under normal or high‐iron dietary conditions.

Duodenal cytochrome b (Cybrd1) ferric reductase functional studies in cells

Dietary non-heme ferric iron is reduced by the ferric reductase enzyme, duodenal cytochrome b (Dcytb), before absorption by the divalent metal transporter 1 (DMT1). A single nucleotide polymorphism (SNP rs10455 mutant) that is located in the last exon of the Dcytb gene was reported in C282Y haemochromatosis HFE subjects. The present work therefore investigated the phenotype of this mutant Dcytb in Chinese hamster ovary (CHO) cells. These cultured cells were transfected with either wild type (WT) or the SNP vector plasmids of Dcytb. Ferric reductase assays were performed in Dcytb transgenic CHO cells using the ferrozine spectrophometric assay protocol. The Dcytb SNP rs10455 showed a gain-of-function capability since ferric reductase activity increased significantly (p < 0.01) in the transgenic cells. Varying ferric reductase activity was found when CHO cells were pretreated with modulators of Dcytb protein expression. Although ferric reductase in endogenous CHO cells increased with deferoxamine or CoCl₂, iron loading with ferric ammonium citrate (FAC) had the opposite effect. Taken together, the study reveals a gain-of-function phenotype for Dcytb rs10455 mutation that could be a putative modifier of colorectal cancer risk, with attendant variability in penetrance among human HFE C282Y homozygotes.

HFE gene: Structure, function, mutations, and associated iron abnormalities

The hemochromatosis gene HFE was discovered in 1996, more than a century after clinical and pathologic manifestations of hemochromatosis were reported. Linked to the major histocompatibility complex (MHC) on chromosome 6p, HFE encodes the MHC class I-like protein HFE that binds beta-2 microglobulin. HFE influences iron absorption by modulating the expression of hepcidin, the main controller of iron metabolism. Common HFE mutations account for ~90% of hemochromatosis phenotypes in whites of western European descent. We review HFE mapping and cloning, structure, promoters and controllers, and coding region mutations, HFE protein structure, cell and tissue expression and function, mouse Hfe knockouts and knockins, and HFE mutations in other mammals with iron overload. We describe the pertinence of HFE and HFE to mechanisms of iron homeostasis, the origin and fixation of HFE polymorphisms in European and other populations, and the genetic and biochemical basis of HFE hemochromatosis and iron overload.

Non-HFE hemochromatosis: pathophysiological and diagnostic aspects

Rare genetic iron overload diseases are an evolving field due to major advances in genetics and molecular biology. Genetic iron overload has long been confined to the classical type 1 hemochromatosis related to the HFE C282Y mutation. Breakthroughs in the understanding of iron metabolism biology and molecular mechanisms led to the discovery of new genes and subsequently, new types of hemochromatosis. To date, four types of hemochromatosis have been identified: HFE-related or type1 hemochromatosis, the most frequent form in Caucasians, and four rare types, named type 2 (A and B) hemochromatosis (juvenile hemochromatosis due to hemojuvelin and hepcidin mutation), type 3 hemochromatosis (related to transferrin receptor 2 mutation), and type 4 (A and B) hemochromatosis (ferroportin disease). The diagnosis relies on the comprehension of the involved physiological defect that can now be explored by biological and imaging tools, which allow non-invasive assessment of iron metabolism. A multidisciplinary approach is essential to support the physicians in the diagnosis and management of those rare diseases.

Hepcidin is linked to hypoferremia in patients with rheumatic valve disease

BACKGROUND AND AIM

Hepcidin has been shown to be an acute phase reactant, induced by infection and inflammation. Ongoing inflammation was shown in rheumatic valve disease (RVD). In this study we want to investigate whether there is a relationship between inflammation and impaired iron metabolism and the role of hepcidin on serum iron levels.

METHODS AND RESULTS

Fourty-six patients with RVD and 34 healthy individuals were included in the study. Serum hepcidin, high-sensitive C-reactive protein (hs-CRP), hemoglobin, hematocrit, iron, iron-binding capacity, ferritin levels were measured. Serum hepcidin levels were significantly increased in patients with RVD than in control group (316 ± 121 ng/mL vs 435 ± 126 ng/mL; P < .001). Serum hs-CRP levels were no significantly higher in the patient group in than in the control group (3.9 ± 3.6 mg/L vs 3.5 ± 3.7 mg/L; P = .521).

CONCLUSION

Hepcidin levels are decreased independently from hs-CRP levels as a compensatory mechanism to increase the iron absorption in response to decreased serum iron levels in patients with RVD.

Keratin 8 variants are infrequent in patients with alcohol-related liver cirrhosis and do not associate with development of hepatocellular carcinoma

Background

Keratins 8/18 (K8/K18) are established hepatoprotective proteins and K8/K18 variants predispose to development and adverse outcome of multiple liver disorders. The importance of K8/K18 in alcoholic liver disease as well as in established cirrhosis remains unknown.

Methods

We analyzed the K8 mutational hot-spots in 261 prospectively followed-up patients with alcoholic cirrhosis (mean follow-up 65 months). PCR-amplified samples were pre-screened by denaturing high-performance liquid chromatography and conspicuous samples were sequenced.

Results

67 patients developed hepatocellular carcinoma (HCC) and 133 died. Fourteen patients harbored amino-acid-altering K8 variants (5xG62C, 8xR341H). The presence of K8 variants did not associate with development of HCC (log-rank=0.5) or death (log-rank=0.7) and no significant associations were obtained for the single K8 variants after a correction for multiple testing was performed.

Conclusions

Keratin variants are expressed in a low percentage of patients with alcoholic cirrhosis and do not influence HCC development. Further studies conducted in larger prospective cohorts are needed to find out whether presence of K8 R341H variant predispose to non-HCC-related liver mortality.

Non-coding keratin variants associate with liver fibrosis progression in patients with hemochromatosis

Background

Keratins 8 and 18 (K8/K18) are intermediate filament proteins that protect the liver from various forms of injury. Exonic K8/K18 variants associate with adverse outcome in acute liver failure and with liver fibrosis progression in patients with chronic hepatitis C infection or primary biliary cirrhosis. Given the association of K8/K18 variants with end-stage liver disease and progression in several chronic liver disorders, we studied the importance of keratin variants in patients with hemochromatosis.

Methods

The entire K8/K18 exonic regions were analyzed in 162 hemochromatosis patients carrying homozygous C282Y HFE (hemochromatosis gene) mutations. 234 liver-healthy subjects were used as controls. Exonic regions were PCR-amplified and analyzed using denaturing high-performance liquid chromatography and DNA sequencing. Previously-generated transgenic mice overexpressing K8 G62C were studied for their susceptibility to iron overload. Susceptibility to iron toxicity of primary hepatocytes that express K8 wild-type and G62C was also assessed.

Results

We identified amino-acid-altering keratin heterozygous variants in 10 of 162 hemochromatosis patients (6.2%) and non-coding heterozygous variants in 6 additional patients (3.7%). Two novel K8 variants (Q169E/R275W) were found. K8 R341H was the most common amino-acid altering variant (4 patients), and exclusively associated with an intronic KRT8 IVS7+10delC deletion. Intronic, but not amino-acid-altering variants associated with the development of liver fibrosis. In mice, or ex vivo, the K8 G62C variant did not affect iron-accumulation in response to iron-rich diet or the extent of iron-induced hepatocellular injury.

Conclusion

In patients with hemochromatosis, intronic but not exonic K8/K18 variants associate with liver fibrosis development.

Effects of hemochromatosis and transferrin gene mutations on iron dyshomeostasis, liver dysfunction and on the risk of Alzheimer's disease

It is now accepted that transition metals, such as iron and copper, are involved in the pathogenesis of the Alzheimer's disease (AD) through their participation in toxic oxidative phenomena. In this context, hemochromatosis (Hfe) and transferrin (Tf) genes are of particular importance, since they play a key role in iron homeostasis. Also, signs of liver distress which accompany metal dysmetabolisms have been shown to be linked to AD. In order to investigate whether and how all these factors are interconnected, in this study we have explored the relationship of the gene variants of Hfe H63D and C282Y and of Tf C2 with serum markers of iron status (iron, ferritin, TF, TF-saturation, ceruloplasmin -CP-, CP and TF serum concentrations (CP/TF) ratio), and of liver function (albumin, transaminases, prothrombin time-prothrombin time (PT)) in a sample of 160 AD patients and 79 healthy elderly controls. Albumin resulted in lower, PT longer and AST/ALT higher ratios in AD patients than in controls, indicating a distress of the liver. Also TF was lower and ferritin higher in AD. Multiple logistic regression backward analyses, performed to evaluate the effects of our biochemical variables upon the probability of developing AD, revealed that a one-unit TF serum-decrease increases the probability of AD by 80%, a one-unit albumin serum-decrease reduces this probability by 20%, and a one-unit increase of AST/ALT ratio generates a 4-fold probability increase. Patients who were carriers of the H63D mutation showed higher levels of iron, lower levels of TF and CP and higher CP/TF ratios, a panel resembling hemochromatosis. This picture was found neither in H63D non-carrier patients, nor in healthy controls. Our results suggest the existence of a link between Hfe mutations and iron abnormalities that increases the probability of developing AD when accompanied by a distress of the liver.

Keratin variants predispose to acute liver failure and adverse outcome: race and ethnic associations

BACKGROUND & AIMS

Keratins 8 and 18 (K8/K18) provide anti-apoptotic functions upon liver injury. The cytoprotective function of keratins explains the overrepresentation of K8/K18 variants in patients with cirrhosis. However, K8/K18 variant-associated susceptibility to acute liver injury, which is well-described in animal models, has not been studied in humans.

METHODS

We analyzed the entire coding regions of KRT8 and KRT18 genes (15 total exons and their exon-intron boundaries) to determine the frequency of K8/K18 variants in 344 acute liver failure (ALF) patients (49% acetaminophen-related) and 2 control groups (African-American [n = 245] and previously analyzed white [n = 727] subjects).

RESULTS

Forty-five ALF patients had significant amino-acid-altering K8/K18 variants, including 23 with K8 R341H and 11 with K8 G434S. K8 variants were significantly more common (total of 42 patients) than K18 variants (3 patients) (P < .001). We found increased frequency of variants in white ALF patients (9.1%) versus controls (3.7%) (P = .01). K8 R341H was more common in white (P = .01) and G434S was more common in African-American (P = .02) ALF patients versus controls. White patients with K8/K18 variants were less likely to survive ALF without transplantation (P = .02). K8 A333A and G434S variants associated exclusively with African Americans (23% combined frequency in African American but none in white controls; P < .0001), while overall, K18 variants were more common in non-white liver-disease subjects compared to whites (2.8% vs 0.6%, respectively; P = .008).

CONCLUSIONS

KRT8 and KRT18 are important susceptibility genes for ALF development. Presence of K8/K18 variants predisposes to adverse ALF outcome, and some variants segregate with unique ethnic and race backgrounds.

Hereditary hemochromatosis: pathogenesis, diagnosis, and treatment

In the late 1800s, hemochromatosis was considered an odd autoptic finding. More than a century later, it was finally recognized as a hereditary, multi-organ disorder associated with a polymorphism that is common among white people: a 845G-->A change in HFE that results in C282Y in the gene product. Hemochromatosis is now a well-defined syndrome characterized by normal iron-driven erythropoiesis and the toxic accumulation of iron in parenchymal cells of liver, heart, and endocrine glands. It can be caused by mutations that affect any of the proteins that limit the entry of iron into the blood. In mice, deletion of the iron hormone hepcidin and any of 8 genes that regulate its biology, including Hfe, transferrin receptor 2 (Tfr2), and hemojuvelin (Hjv) (which all sense the accumulation of iron that hepcidin corrects) or ferroportin (Fpn) (the cellular iron exporter down-regulated by hepcidin), cause iron overload but not organ disease. In humans, loss of TfR2, HJV, and hepcidin itself or FPN mutations result in full-blown hemochromatosis. Unlike these rare instances, in white people, homozygotes for C282Y polymorphism in HFE are numerous, but they are only predisposed to hemochromatosis; complete organ disease develops in a minority, when these individuals abuse alcohol or from other unidentified modifying factors. HFE gene testing can be used to diagnose hemochromatosis, but analyses of liver histology and clinical features are still required to identify patients with rare, non-HFE forms of the disease. The role of hepcidin in the pathogenesis of hemochromatosis reveals its similarities to endocrine diseases such as diabetes and indicates new approaches to diagnosis and management of this common disorder in iron metabolism.

Demographic correlates of low hemoglobin deferral among prospective whole blood donors

BACKGROUND

Approximately 10% of attempted blood donations are not allowed because of low hemoglobin (Hb) deferral.

STUDY DESIGN AND METHODS

Low Hb deferrals were tracked in more 715,000 whole blood donors at six blood centers across the United States. A multivariable logistic regression model was developed to comprehensively assess demographic correlates for low Hb deferral.

RESULTS

Demographic factors significantly associated with low Hb deferral include female sex (11 times greater odds than males), increasing age in men (men over 80 have 29 times greater odds than men under 20), African American race (2-2.5 times greater odds than Caucasians), Hispanic ethnicity in women (1.29 times greater odds than Caucasian women), and weight in men (men under 124 pounds have 2.5 times greater odds than men over 200 pounds). Interestingly, increasing donation frequency is associated with decreased odds for low Hb deferral (women with one donation in the previous 12 months have two times greater odds than those with six donations).

CONCLUSIONS

Low Hb deferral is associated with female sex, older age, African American race/ethnicity, and lower body weight in men. An inverse association with donation frequency suggests a selection bias in favor of donors able to give more frequently. These data provide useful information that can be utilized to manage blood donors to limit low Hb deferrals and assist in policy decisions such as changing the Hb cutoff or permissible frequency of donation. They also generate hypotheses for new research of the causes of anemia in defined groups of donors.

Relationship between gene expression of duodenal iron transporters and iron stores in hemochromatosis subjects

To test the hypothesis that differences in duodenal iron absorption may explain the variable phenotypic expression among HFE C282Y homozygotes, we have compared relative gene expression of duodenal iron transporters among C282Y homozygotes [hereditary hemochromatosis (HH)] with and without iron overload. Duodenal biopsy samples were analyzed using real-time PCR for expression of DMT1, FPN1, DCYTB, and HEPH relative to GAPDH from 23 C282Y homozygotes, including 5 "nonexpressors" (serum ferritin < upper limit of normal and absence of phenotypic features of hemochromatosis) and 18 "expressors." Four subjects of wild type for HFE mutations without iron overload or liver disease served as controls. There was a significant difference in expression of DMT1 (P = 0.03) and DMT1(IRE) (P = 0.0013) but not FPN1, DCYTB, or HEPH between groups. Expression of DMT1(IRE) was increased among HH subjects after phlebotomy compared with untreated (P = 0.006) and nonexpressor groups (P = 0.026). A positive relationship was observed among all HH subjects regardless of phenotype or treatment status between relative expression of FPN1 and DMT1 (r = 0.5854, P = 0.0021), FPN1, and DCYTB (r = 0.5554, P = 0.0040), FPN1 and HEPH (r = 0.5100, P = 0.0092), and DCYTB and HEPH (r = 0.5400, P = 0.0053). In summary, phlebotomy is associated with upregulation of DMT1(IRE) expression in HH subjects. HFE C282Y homozygotes without phenotypic expression do not have significantly decreased duodenal gene expression of iron transport genes compared with HH subjects with iron overload. There is coordinated regulation between duodenal expression of FPN1 and DMT1, FPN1 and DCYTB, and FPN1 and HEPH and also DCYTB and HEPH in HH subjects regardless of phenotype.

Anemia or low hemoglobin levels preceding Parkinson disease: a case-control study

OBJECTIVE

It has been suggested that anemia may be a risk factor for dementia, for restless legs syndrome, and for Parkinson disease (PD). Thus, we investigated the association of anemia with the subsequent risk of PD using a case-control study design.

METHODS

We used the medical records-linkage system of the Rochester Epidemiology Project to identify 196 subjects who developed PD in Olmsted County, Minnesota, from 1976 through 1995. Each incident case was matched by age (+/-1 year) and sex to a general population control. We reviewed the complete medical records of cases and controls in the system to detect anemia defined using the World Health Organization criteria.

RESULTS

Anemia was more common in the history of cases than of controls (odds ratio 2.00, 95% confidence interval 1.31-3.06, p = 0.001). The association remained significant after adjustment for cigarette smoking, exposure to pesticides, or hysterectomy (in women). The association was not significantly different between men and women, or between PD patients with or without rest tremor. Analyses stratified by time of onset of anemia showed a greater association for anemia that started 20 to 29 years before the onset of PD. Hemoglobin levels were slightly but consistently lower in cases than in controls across all ages.

CONCLUSIONS

Our results support an association between anemia experienced early in life and the later development of Parkinson disease. The interpretation of this association remains uncertain.

A novel association between a SNP in CYBRD1 and serum ferritin levels in a cohort study of HFE hereditary haemochromatosis

There is emerging evidence that there are genetic modifiers of iron indices for HFE gene mutation carriers at risk of hereditary hemochromatosis. A random sample, stratified by HFE genotype, of 863 from a cohort of 31 192 people of northern European descent provided blood samples for genotyping of 476 single nucleotide polymorphisms (SNPs) in 44 genes involved in iron metabolism. Single SNP association testing, using linear regression models adjusted for sex, menopause and HFE genotype, was conducted for four continuously distributed outcomes: serum ferritin (log transformed), transferrin saturation, serum transferrin, and serum iron. The SNP rs884409 in CYBRD1 is a novel modifier specific to HFE C282Y homozygotes. Median unadjusted serum ferritin concentration decreased from 1194 microg/l (N = 27) to 387 microg/l (N = 16) for male C282Y homozygotes and from 357 microg/l (N = 42) to 69 microg/l (N = 12) for females, comparing those with no copies to those with one copy of rs884409. Functional testing of this CYBRD1 promoter polymorphism using a heterologous expression assay resulted in a 30% decrease in basal promoter activity relative to the common genotype (P = 0.004). This putative genetic modifier of iron overload expression accounts for 11% (95% CI 0.4%, 22.6%) of the variance in serum ferritin levels of C282Y homozygotes.

Regulation of hepcidin and iron-overload disease

Hepcidin, a 25-amino-acid antimicrobial peptide, is the central regulator of iron homeostasis. Hepcidin transcription is upregulated by inflammatory cytokines, iron, and bone morphogenetic proteins and is downregulated by iron deficiency, ineffective erythropoiesis, and hypoxia. The iron transporter ferroportin is the cognate receptor of hepcidin and is destroyed as a result of interaction with the peptide. Except for inherited defects of ferroportin and hepcidin itself, all forms of iron-storage disease appear to arise from hepcidin dysregulation. Studies using multiple approaches have begun to delineate the molecular mechanisms that regulate hepcidin expression, particularly at the transcriptional level. Knowledge of the regulation of hepcidin by inflammation, iron, erythropoiesis, and hypoxia will lead to an understanding of the pathogenesis of primary hemochromatosis, secondary iron overload, and anemia of inflammatory disease.

Genetics of hereditary hemochromatosis: a clinical perspective

Hereditary hemochromatosis due to homozygosity for the C282Y mutation in the HFE gene product is the most common autosomal recessive genetic disorder in populations of northern European descent, where it attains a maximum prevalence of approximately one in 200. Cross-sectional and longitudinal studies have revealed that clinically significant iron-overload disease develops in at least 28% of male and 1% of female HFE C282Y homozygotes. The relatively low clinical penetrance is largely unexplained. Current evidence suggests a limited role for digenic inheritance of mutations in iron homeostasis genes in modifying the penetrance of hemochromatosis. Male gender is a strong genetic factor, promoting expression of clinical disease. Dietary intake of alcohol and noncitrus fruit may also act as important environmental modifiers of penetrance. With genetic analyses becoming simpler to perform, new genetic modifiers of hepatic iron loading and liver fibrogenesis are likely to be forthcoming.

Severity of iron overload of proband determines serum ferritin levels in families with HFE-related hemochromatosis: the HEmochromatosis FAmily Study

BACKGROUND/AIMS

In families of patients with clinically detected hereditary hemochromatosis (HH) early screening has been suggested to prevent morbidity and mortality. Here, we aim to identify determinants for iron overload in first-degree family members of C282Y homozygous probands with clinically detected HH.

METHODS

Data on HFE-genotype, iron parameters, demographics, lifestyle factors and health, were collected from 224 Dutch C282Y homozygous patients with clinically diagnosed HH and 735 of their first-degree family members (FDFM), all participating in the HEmochromatosis FAmily Study (HEFAS).

RESULTS

The best predictive multivariable model forecasted 45% of variation of the serum ferritin levels. In this model severity of iron overload in the proband significantly predicted serum ferritin levels in FDFM. Other significant determinants in this model consisted of C282Y homozygosity, compound heterozygosity, age at testing for serum ferritin and supplemental iron intake, whereas a low body mass index showed a protective effect.

CONCLUSIONS

This study provides a model to assess the risk of development of iron overload for relatives of probands with HH. These results might be instrumental in the development of an optimal strategy for future family screening programs.

Changes in hepatic gene expression in dogs with experimentally induced nutritional iron deficiency

BACKGROUND AND OBJECTIVE

We investigated hepatic gene expression in dogs with experimentally induced nutritional iron deficiency (ID). Our hypothesis was that ID would result in decreased hepcidin gene expression, and possibly in altered expression of other genes associated with iron metabolism.

METHODS

Liver biopsies were collected from each of 3 dogs before induction of ID, at the point of maximal ID, and after resolution of ID. Using Affymetrix microarray technology and analytical tools specifically designed for microarray data, we identified genes that had at least a 2-fold change in expression in response to ID. Four genes were selected for further analysis by reverse transcriptase PCR (RT-PCR).

RESULTS

Dogs with ID had markedly decreased expression of the hepcidin gene (mean decrease of 40-fold for one probe and >100-fold for another probe) and increased expression of the transferrin receptor gene (mean increase of >7-fold). There was also mildly decreased expression of the "similar to calreticulin" gene and a gene of unknown function. Results of RT-PCR analysis were consistent with microarray findings.

CONCLUSION

Changes in hepcidin and transferrin receptor gene expression were consistent with the known biology of iron metabolism. The decrease in expression of a gene identified as "similar to calreticulin," while not statistically significant, was consistent with the findings of other investigators that suggest iron plays a role in calreticulin expression.

Systemic iron homeostasis and the iron-responsive element/iron-regulatory protein (IRE/IRP) regulatory network

The regulation and maintenance of systemic iron homeostasis is critical to human health. Iron overload and deficiency diseases belong to the most common nutrition-related pathologies across the globe. It is now well appreciated that the hormonal hepcidin/ferroportin system plays an important regulatory role for systemic iron metabolism. We review recent data that uncover the importance of the cellular iron-responsive element/iron-regulatory protein (IRE/IRP) regulatory network in systemic iron homeostasis. We also discuss how the IRE/IRP regulatory system communicates with the hepcidin/ferroportin system to connect the control networks for systemic and cellular iron balance.

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.

Current approach to hemochromatosis

Iron overload diseases of genetic origin are an ever changing world, due to major advances in genetics and molecular biology. Five major categories are now established: HFE-related or type1 hemochromatosis, frequently found in Caucasians, and four rarer diseases which are type 2 (A and B) hemochromatosis (juvenile hemochromatosis), type 3 hemochromatosis (transferrin receptor 2 hemochromatosis), type 4 (A and B) hemochromatosis (ferroportin disease), and a(hypo)ceruloplasminemia. Increased duodenal iron absorption and enhanced macrophagic iron recycling, both due to an impairment of hepcidin synthesis, account for the development of cellular excess in types 1, 2, 3, and 4B hemochromatosis whereas decreased cellular iron egress is involved in the main form of type 4A) hemochromatosis and in aceruloplasminemia. Non-transferrin bound iron plays an important role in cellular iron excess and damage. The combination of magnetic resonance imaging (for diagnosing visceral iron overload) and of genetic testing has drastically reduced the need for liver biopsy. Phlebotomies remain an essential therapeutic tool but the improved understanding of the intimate mechanisms underlying these diseases paves the road for innovative therapeutic approaches.

Characteristics of participants with self-reported hemochromatosis or iron overload at HEIRS study initial screening

There are few descriptions of young adults with self-reported hemochromatosis or iron overload (H/IO). We analyzed initial screening data in 7,343 HEmochromatosis and IRon Overload Screening (HEIRS) Study participants ages 25-29 years, including race/ethnicity and health information; transferrin saturation (TS) and ferritin (SF) measurements; and HFE C282Y and H63D genotypes. We used denaturing high-pressure liquid chromatography and sequencing to detect mutations in HJV, TFR2, HAMP, SLC40A1, and FTL. Fifty-one participants reported previous H/IO; 23 (45%) reported medical conditions associated with H/IO. Prevalences of reports of arthritis, diabetes, liver disease or liver cancer, heart failure, fertility problems or impotence, and blood relatives with H/IO were significantly greater in participants with previous H/IO reports than in those without. Only 7.8% of the 51 participants with previous H/IO reports had elevated TS; 13.7% had elevated SF. Only one participant had C282Y homozygosity. Three participants aged 25-29 years were heterozygous for potentially deleterious mutations in HFE2, TFR2, and HAMP promoter, respectively. Prevalences of self-reported conditions, screening iron phenotypes, and C282Y homozygosity were similar in 1,165 participants aged 30 years or greater who reported previous H/IO. We conclude that persons who report previous H/IO diagnoses in screening programs are unlikely to have H/IO phenotypes or genotypes. Previous H/IO reports in some participants could be explained by treatment that induced iron depletion before initial screening, misdiagnosis, or participant misunderstanding of their physician or the initial screening questionnaire.

HFE C282Y homozygotes aged 25-29 years at HEIRS Study initial screening

We characterized HFE C282Y homozygotes aged 25-29 years in the HEmochromatosis and IRon Overload Screening (HEIRS) Study using health questionnaire responses, transferrin saturation (TfSat), serum ferritin (SF), and HFE genotyping. In eight homozygotes, we used denaturing high-performance liquid chromatography and sequencing to search for HFE2 (= HJV), TFR2, HAMP, SLC40A1 (= FPN1), and FTL mutations. Sixteen of 4,008 White or Hispanic participants aged 25-29 years had C282Y homozygosity (15 White, 1 Hispanic); 15 were previously undiagnosed. Eleven had elevated TfSat; nine had elevated SF. None reported iron overload-associated abnormalities. No deleterious non-HFE mutations were detected. The prevalence of C282Y homozygosity in White or Hispanic HEIRS Study participants aged 25-29 years did not differ significantly from the prevalence of C282Y homozygosity in older White or Hispanic HEIRS Study participants. The prevalences of reports of iron overload-associated abnormalities were not significantly different in these 16 C282Y homozygotes and in HFE wt/wt control participants aged 25-29 years who did not report having hemochromatosis or iron overload. We conclude that C282Y homozygotes aged 25-29 years diagnosed by screening infrequently report having iron overload-associated abnormalities, although some have elevated SF. Screening using an elevated TfSat criterion would fail to detect some C282Y homozygotes aged 25-29 years.

SLC40A1 c.1402G-->a results in aberrant splicing, ferroportin truncation after glycine 330, and an autosomal dominant hemochromatosis phenotype

BACKGROUND/AIMS

To determine the molecular basis of a mild hemochromatosis phenotype in a man of Scottish-Irish descent.

METHODS

We sequenced genomic DNA to detect mutations of HFE, SLC40A1, TFR2, HAMP, and HFE2. RNA isolated from blood mononuclear cells was used to make cDNA. RT-PCR was performed to amplify ferroportin from cDNA, and amplified products were visualized by electrophoresis and sequenced.

RESULTS

The proband was heterozygous for the novel mutation c.1402G-->A (predicted G468S) in exon 7 of the ferroportin gene (SLC40A1). Located in the last nucleotide before the splice junction, this mutation results in aberrant splicing to a cryptic upstream splice site located at nt 990 within the same exon. This causes truncation of ferroportin after glycine 330 and the addition of 4 irrelevant amino acids before terminating. The truncated ferroportin protein, missing its C-terminal 241 amino acids, would lack all structural motifs beyond transmembrane region 7. The patient was also heterozygous for the common HFE H63D polymorphism, but did not have coding region mutations in TFR2, HAMP, or HFE2.

CONCLUSIONS

We conclude that this patient represents a unique example of hemochromatosis due to a single base-pair mutation of SLC40A1 that results in aberrant splicing and truncation of ferroportin.

Screening for hemochromatosis by measuring ferritin levels: a more effective approach

Because the penetrance of HFE hemochromatosis is low, traditional population screening measuring the transferrin saturation is unlikely to be cost-effective because the majority of subjects detected neither have clinical disease nor are likely to develop it. Three independent studies show that only patients with serum ferritin concentrations more than 1000 microg/L are at risk for cirrhosis, one of the main morbidities of hemochromatosis. Among 29,699 white subjects participating in the Scripps/Kaiser hemochromatosis study, only 59 had serum ferritin levels more than 1000 microg/L; 24 had homozygous mutant or compound heterozygous mutant HFE genotypes. In all but 5 of the other subjects, the causes of elevated ferritin were excessive alcohol intake, cancer, or liver disease. Screening for hemochromatosis with serum ferritin levels will detect the majority of patients who will be clinically affected and may detect other clinically significant disease in patients who do not have hemochromatosis genotypes. Because the ferritin level of the majority of adult homozygotes for HFE mutations does not rise over long periods of time, excluding subjects with serum ferritin levels less than or equal to 1000 microg/L should not result in missed opportunities for early treatment of patients who could benefit.

Keratins let liver live: Mutations predispose to liver disease and crosslinking generates Mallory-Denk bodies

Keratin polypeptides 8 and 18 (K8/K18) are the cytoskeletal intermediate filament proteins of hepatocytes while K8/K18/K19 are the keratins of hepatobiliary ductal cells. Hepatocyte K8/K18 are highly abundant and behave as stress proteins with injury-inducible expression. Human association studies show that K8/K18 germline heterozygous mutations predispose to end-stage liver disease of multiple etiologies ( approximately 3 fold increased risk), and to liver disease progression in patients with chronic hepatitis C infection. These findings are supported by extensive transgenic mouse and ex vivo primary hepatocyte culture studies showing that K8 or K18 mutations predispose the liver to acute or subacute injury and promote apoptosis and fibrosis. Mutation-associated predisposition to liver injury is likely related to mechanical and nonmechanical keratin functions including maintenance of cell integrity, protection from apoptosis and oxidative injury, serving as a phosphate sponge, regulation of mitochondrial organization/function and protein targeting. These functions are altered by mutation-induced changes in keratin phosphorylation, solubility and filament organization/reorganization. Keratins are also the major constituents of Mallory-Denk bodies (MDBs). A toxin-induced K8>K18 ratio, and keratin crosslinking by transglutaminase-2 play essential roles in MDB formation. Furthermore, intracellular or cell-released K18 fragments, generated by caspase-mediated proteolysis during apoptosis serve as markers of liver injury. Therefore, K8 and K18 are cytoprotective stress proteins that play a central role in guarding hepatocytes from apoptosis. Keratin involvement in liver disease is multi-faceted and includes modulating disease progression upon mutation, formation of MDBs in response to unique forms of injury, and serving as markers of epithelial cell death.

Hemochromatosis: an endocrine liver disease

This review acknowledges the recent and dramatic advancement in the field of hemochromatosis and highlights the surprising analogies with a prototypic endocrine disease, diabetes. The term hemochromatosis should refer to a unique clinicopathologic subset of iron-overload syndromes that currently includes the disorder related to the C282Y homozygote mutation of the hemochromatosis protein HFE (by far the most common form of hemochromatosis) and the rare disorders more recently attributed to the loss of transferrin receptor 2, HAMP (hepcidin antimicrobial peptide), or hemojuvelin or to certain ferroportin mutations. The defining characteristic of this subset is failure to prevent unneeded iron from entering the circulatory pool as a result of genetic changes compromising the synthesis or activity of hepcidin, the iron hormone. Like diabetes, hemochromatosis results from the complex, nonlinear interaction between genetic and acquired factors. Depending on the underlying mutation, the coinheritance of modifier genes, the presence of nongenetic hepcidin inhibitors, and other host-related factors, the clinical manifestation may vary from simple biochemical abnormalities to severe multiorgan disease. The recognition of the endocrine nature of hemochromatosis suggests intriguing possibilities for new and more effective approaches to diagnosis and treatment.

Iron storage disease: facts, fiction and progress

There are many forms of iron storage disease, some hereditary and some acquired. The most common of the hereditary forms is HFE-associated hemochromatosis, and it is this disorder that is the main focus of this presentation. The body iron content is regulated by controlling absorption, and studies in the past decade have clarified, in part, how this regulation functions. A 25-amino-acid peptide hepcidin is up-regulated by iron and by inflammation, and it inhibits iron absorption and traps iron in macrophages by binding to and causing degradation of the iron transport protein ferroportin. Most forms of hemochromatosis results from dysregulation of hepcidin or defects of hepcidin or ferroportin themselves. Hereditary hemochromatosis was once considered to be very rare, but in the 1970s and 1980s, with the introduction of better diagnostic tests, it was considered the most common disease among Europeans. Controlled epidemiologic studies carried out in the last decade have shown, however, the disease itself actually is rare, and only its genotype and associated biochemical changes that are common. We do not understand why only a few homozygotes develop severe disease. It now seems unlikely that there are important modifying genes, and although alcohol is known to have some effect, excess drinking probably plays only a modest role in determining the hemochromatosis phenotype. Hereditary hemochromatosis is readily treated by phlebotomy. Secondary forms of the disease require chelation therapy, and the recent introduction of effective oral chelating agents is an important step forward in treating patients with disorders in which iron overload often proves to be fatal, such as thalassemia, myelodysplastic anemias, and dyserythropoietic anemias. While much has been learned about the regulation of iron homeostasis in the past decade, many mysteries remain and represent challenges that will keep us occupied for years to come.

A genome-wide linkage scan for iron phenotype quantitative trait loci: the HEIRS Family Study

Iron overload phenotypes in persons with and without hemochromatosis are variable. To investigate this further, probands with hemochromatosis or evidence of elevated iron stores and their family members were recruited for a genome-wide linkage scan to identify potential quantitative trait loci (QTL) that contribute to variation in transferrin saturation (TS), unsaturated iron-binding capacity (UIBC), and serum ferritin (SF). Genotyping utilized 402 microsatellite markers with average spacing of 9 cM. A total of 943 individuals, 64% Caucasian, were evaluated from 174 families. After adjusting for age, gender, and race/ethnicity, there was evidence for linkage of UIBC to chromosome 4q logarithm of the odds (LOD) = 2.08, p = 0.001) and of UIBC (LOD = 9.52), TS (LOD = 4.78), and SF (LOD = 2.75) to the chromosome 6p region containing HFE (each p < 0.0001). After adjustments for HFE genotype and other covariates, there was evidence of linkage of SF to chromosome 16p (LOD = 2.63, p = 0.0007) and of UIBC to chromosome 5q (LOD = 2.12, p = 0.002) and to chromosome 17q (LOD = 2.19, p = 0.002). We conclude that these regions should be considered for fine mapping studies to identify QTL that contribute to variation in SF and UIBC.

Haptoglobin is degraded by iron in C57BL/6 mice: a possible link with endoplasmic reticulum stress

BACKGROUND

Haptoglobin is a glycoprotein produced mainly by the liver and secreted into the circulation. Haptoglobin, by virtue of its high affinity for hemoglobin, protects the tissues against hemoglobin-induced oxidative damage and allows heme iron recycling. Haptoglobin synthesis is controlled by various effectors, however, little is known concerning its regulation by iron. Haptoglobin regulation in C57BL/6 and 129sv mice fed on an iron-rich diet for 3 weeks was thus undertaken.

RESULTS

Iron induced a dramatic post-transcriptional decrease of liver and serum haptoglobin in C57BL/6 mice. In contrast, no alteration of haptoglobin expression was detected in 129sv mice. We assumed that the oxidative stress induced by iron in C57BL/6 mice altered the endoplasmic reticulum (ER) environment, leading to the incorrect folding of haptoglobin and its subsequent degradation. To test this hypothesis, the levels of the RE chaperone GRP78 were measured. This chaperone is known to assist protein folding in the RE during pathophysiological conditions. Interestingly, we found that the mRNA and protein levels of GRP78 were decreased in iron-fed C57BL/6 mice, while they were unchanged in iron-fed 129sv mice. These results suggest that the correct processing of haptoglobin (glycosylation, disulfide linkage, folding, and assembly) might be sensitive to ER stress and that, in the absence of GRP78-mediated assistance, Hp is degraded.

CONCLUSION

Our data demonstrate that iron regulates haptoglobin synthesis in C57BL/6 mice and suggest a possible link with iron-induced ER stress.

Genetic variation in Mon1a affects protein trafficking and modifies macrophage iron loading in mice

We undertook a quantitative trait locus (QTL) analysis in mice to identify modifier genes that might influence the severity of human iron disorders. We identified a strong QTL on mouse chromosome 9 that differentially affected macrophage iron burden in C57BL/10J and SWR/J mice. A C57BL/10J missense allele of an evolutionarily conserved gene, Mon1a, cosegregated with the QTL in congenic mouse lines. We present evidence that Mon1a is involved in trafficking of ferroportin, the major mammalian iron exporter, to the surface of iron-recycling macrophages. Differences in amounts of surface ferroportin correlate with differences in cellular iron content. Mon1a is also important for trafficking of cell-surface and secreted molecules unrelated to iron metabolism, suggesting that it has a fundamental role in the mammalian secretory apparatus.

SLC40A1 Q248H allele frequencies and Q248H-associated risk of non-HFE iron overload in persons of sub-Saharan African descent

The ferroportin polymorphism SLC40A1 Q248H (exon 6, cDNA 744G-->T; Gln248His) occurs in persons of sub-Saharan African descent with and without iron overload, and is associated with elevated serum ferritin concentrations (SF). However, the risk of iron overload associated with Q248H has not been defined. We tabulated previously reported Q248H allele frequency estimates in African-Americans and Native Africans, and computed the risk of iron overload associated with Q248H in subjects who lacked HFE C282Y. The aggregate Q248H allele frequency in 1038 African-Americans in two cohorts from Alabama and one cohort each from Washington, DC and California was 0.0525 (95% CI: 0.0451, 0.0652); there was no significant difference in frequencies across these cohorts. The aggregate frequency in 259 Natives from southeast Africa in two cohorts was 0.0946 (95% CI: 0.0694, 0.1198); the difference between the frequencies of these cohorts was not significant. The aggregate Q248H frequencies in African-Americans and Native Africans differed significantly (0.0525 vs. 0.0946, respectively; p=0.0021). There were reports of 24 unrelated African-Americans and 15 unrelated Native Africans without HFE C282Y who had iron overload. In African-Americans, the odds ratio (OR) of Q248H-associated risk of iron overload using 610 C282Y-negative control subjects unselected for SF was 1.57 (95% CI: 0.52, 4.72; p=0.29). In Native Africans, the OR using 208 control subjects unselected for SF was 1.05 (95% CI: 0.28, 3.90; p=0.58). We conclude that the frequency of SLC40A1 Q248H is significantly lower in African-Americans than in Native Africans. Although OR estimates of iron overload in African-Americans and Native Africans with Q248H were greater than unity, the increased OR were not statistically significant.

The G277S transferrin mutation does not affect iron absorption in iron deficient women

BACKGROUND

Iron deficiency anaemia is one of the most important nutritional diseases, with high prevalence worldwide. The G277S transferrin mutation has been implicated as a risk factor for iron deficiency in menstruating women. However, the subject is controversial and there are no data concerning the possible influence of this polymorphism on iron absorption.

AIM OF THE STUDY

To undertake a pilot study to investigate the effect of carrying the G277S transferrin mutation on non-haem iron absorption from a meal in young menstruating women compared to wild-type controls.

METHODS

Menstruating women with low iron stores (serum ferritin < 30 microg/l) or who had suffered from iron deficiency anaemia or had a family history of anaemia were recruited (n = 162). Haematological parameters were analysed, including haemoglobin, ferritin, total-iron binding capacity and transferrin saturation. Non-haem iron absorption from a meal was measured in 25 non-anaemic women either with the G277S/G277G (n = 10) or the wild type G277G/G277G (n = 15) genotype. The incorporation of stable isotopes of iron into erythrocytes was used to measure absorption.

RESULTS AND CONCLUSIONS

There were no significant differences in iron status indices or non-haem iron absorption between genotypes. However, G277S carriers did not show the usual inverse association between iron stores and non-haem iron absorption. Further studies should focus on the effects of a combination of polymorphisms in iron metabolism genes on iron absorption.

Helicobacter pylori infection and HFE hemochromatosis

Helicobacter pylori infections are associated with iron deficiency, even in the absence of bleeding. To determine whether H. pylori infection plays a role in modifying the phenotype of patients homozygous for the c.845 G > A (C282Y) mutation of the HFE gene we studied 79 homozygous women and 76 homozygous men, comparing the pretreatment hemoglobin, MCV, serum ferritin, transferrin saturation of those who were seropositive and seronegative for H. pylori. No difference between seropositive and seronegative homozytoes was found. There was also no difference between seropositive and seronegative control subjects. We also compared the total iron of 56 of the male and 32 of the female homozygotes as determined by serial phlebotomy. No significant difference was found.

Iron overload and prolonged ingestion of iron supplements: clinical features and mutation analysis of hemochromatosis-associated genes in four cases

We evaluated and treated four white adults (one man, three women) who had iron overload associated with daily ingestion of iron supplements for 7, 15, 35, and 61 years, respectively. We performed HFE mutation analysis to detect C282Y, H63D, and S65C in each patient; in two patients, HFE exons were sequenced. In two patients, direct sequencing was performed to detect coding region mutations of TFR2, HAMP, FPN1, HJV, and ALAS2. Patients 1-4 ingested 153, 547, 1,341, and 4,898 g of inorganic iron as supplements. Patient 1 had hemochromatosis, HFE C282Y homozygosity, and beta-thalassemia minor. Patient 2 had spherocytosis and no HFE coding region mutations. Patient 3 had no anemia, a normal HFE genotype, and no coding region mutations in HAMP, FPN1, HJV, or ALAS2; she was heterozygous for the TFR2 coding region mutation V583I (nt 1,747 G-->A, exon 15). Patient 4 had no anemia and no coding region mutations in HFE, TFR2, HAMP, FPN1, HJV, or ALAS2. Iron removed by phlebotomy was 32.4, 10.4, 15.2, and 4.0 g, respectively. There was a positive correlation of log(10) serum ferritin and the quantity of iron removed by phlebotomy (P = 0.0371). Estimated absorption of iron from supplements in patients 1-4 was 20.9%, 1.9%, 1.1%, and 0.08%. We conclude that the clinical phenotypes and hemochromatosis genotypes of adults who develop iron overload after ingesting iron supplements over long periods are heterogeneous. Therapeutic phlebotomy is feasible and effective, and would prevent complications of iron overload.

Keratin variants associate with progression of fibrosis during chronic hepatitis C infection

Keratins 8 and 18 (K8/K18) protect the liver from various forms of injury. Studies of liver explants from a large cohort of U.S. patients showed that K8/K18 mutations confer a risk to developing end-stage liver diseases, though which diseases are preferentially involved is unknown. We tested the hypothesis that K8/K18 variants are associated with chronic hepatitis C (CHC) and that their presence correlates with progression of fibrosis. Genomic DNA was isolated from peripheral blood of a well-characterized German cohort of 329 patients with CHC infection. Exonic regions were PCR-amplified and analyzed using denaturing high-performance liquid chromatography and DNA sequencing. Our findings showed: (1) amino acid altering keratin heterozygous variants in 24 of 329 CHC patients (7.3%) and non-coding heterozygous variants in 26 patients (7.8%), and (2) 3 new exonic K8 variants (T26R/G55A/A359T); 6 novel non-coding variants and one K18 coding variant (K18 S230T; 2 patients). The most common variants were K8 R341H (10 patients), K8 G62C (6 patients) and K8 I63V (4 patients). A novel and exclusive association of an intronic KRT8 IVS7+10delC deletion in all 10 patients with K8 R341H was observed. Notably, there was a significant association of exonic, but not of intronic K8 variants with increased fibrosis. In conclusion, previously described and novel K8 variants are present in a German population and collectively associate with progression of fibrosis in CHC infection. The unique 100% segregation of the most common K8 variant, R341H, with an intronic deletion suggests that one of these two genetic changes might lead to the other.