Iron absorption by heterozygous carriers of the HFE C282Y mutation associated with hemochromatosis

Differences in nonheme iron absorption between healthy adults of East Asian or Northern European ancestry from the Iron Genes in East Asian and Northern European Adults Study (FeGenes): A cross-sectional stable iron isotope study

BACKGROUND

Because humans lack mechanisms for excreting excess iron (Fe), dietary Fe absorption must be tightly regulated to ensure optimal Fe levels. We previously showed that East Asian (EA) individuals have higher Fe stores compared with Northern European (NE) individuals, but the physiological basis for this difference is unknown.

OBJECTIVES

Our aim is to compare nonheme Fe absorption and its regulation in healthy participants of genetically confirmed EA or NE ancestry.

METHODS

Participants of this cross-sectional study were males and premenopausal, nonpregnant females of EA (n = 253) or NE (n = 251) ancestry, aged 18-50 y, and without obesity. Participants ingested a stable 57Fe isotope as a FeSO4 solution mixed with syrup. Percent Fe absorption was calculated based on erythrocyte 57Fe enrichment 2 wk postdosing measured using magnetic sector thermal ionization mass spectrometry and normalized to a fixed serum ferritin (SF) level. Fe status traits (SF, soluble transferrin receptor, total body Fe), hormones (hepcidin, erythropoietin, erythroferrone), and inflammatory markers were evaluated.

RESULTS

SF-corrected % Fe absorption was higher in EA females [27.4 (95% confidence interval (CI): 23.4, 32.0)] and males [19.8 (95% CI: 14.9, 26.4)] compared with NE females [14.8 (95% CI: 11.8, 18.2)] and males [14.9 (95% CI: 11.8, 18.9)], respectively (both P < 0.001). Percent Fe absorption was consistently associated with hepcidin in EA males [β = -0.64; standard error (SE) = 0.24; P = 0.008] and females (β = -0.61; SE = 0.12; P < 0.001), and in NE males (β = -0.63; SE = 0.22; P = 0.005) and females (β = -0.71; SE = 0.14; P < 0.001). Percent Fe absorption was linearly associated with SF in EA females (β = -0.57; SE = 0.09; P < 0.001) and NE males (β = -0.73; SE = 0.21; P < 0.001) and females (β = -0.68; SE = 0.12; P < 0.001), but in EA males, a U-shaped relationship was observed (P = 0.003).

CONCLUSIONS

EA individuals have a greater SF-corrected Fe absorption compared with NE individuals. Increased Fe absorption and resulting excess Fe accumulation suggests that EA individuals may be at greater risk of Fe overload-related diseases. Further studies are needed to evaluate the long-term implications of these findings. This trial was registered at clinicaltrials.gov as NCT04198545.

Managing Genetic Hemochromatosis: An Overview of Dietary Measures, Which May Reduce Intestinal Iron Absorption in Persons With Iron Overload

Genetic hemochromatosis causes iron overload by excess absorption of dietary iron, due to a decreased expression of hepcidin. The objective was to elaborate dietary recommendations that can reduce intestinal iron absorption in hemochromatosis patients, based on our present knowledge of the iron contained in nutrients and the mechanisms of iron uptake. This is a narrative review. Literature search in PubMed and Google Scholar of papers dealing with iron absorption from the diet was conducted. Most important proposed dietary recommendations are: 1) Choose a varied vegetarian, semi-vegetarian or flexitarian diet. A “veggie-lacto-ovo-poultry-pescetarian” diet seems optimal. Avoid iron enriched foods and iron supplements. 2) Eat many vegetables and fruits, at least 600 g per day. Choose protein rich pulses and legumes (e.g., kidney- and soya beans). Fresh fruits should be eaten between meals. 3) Abstain from red meat from mammals and choose the lean, white meat from poultry. Avoid processed meat, offal and blood containing foods. Eat no more than 200 g meat from poultry per week. Choose fish, eggs, vegetables and protein rich legumes the other days. Eat fish two to four times a week as main course, 350 - 500 g fish per week, of which half should be fat fish. 4) Choose whole grain products in cereals and bread. Avoid iron enriched grains. Choose non-sourdough, yeast-fermented bread with at least 50% whole grain. 5) Choose vegetable oils, and low-fat dairy products. 6) Eat less sugar and salt. Choose whole foods and foods with minimal processing and none or little added sugar or salt. 7) Quench your thirst in water. Drink green- or black tea, coffee, or low-fat milk with the meals, alternatively water or non-alcoholic beer. Fruit juices must be consumed between meals. Abstain from alcoholic beverages. Drink soft drinks, non-alcoholic beer, or non-alcoholic wine instead. These advices are close to the official Danish dietary recommendations in 2021. In the management of hemochromatosis, dietary modifications that lower iron intake and decrease iron bioavailability may provide additional measures to reduce iron uptake from the foods and reduce the number of phlebotomies. However, there is a need for large, prospective, randomized studies that specifically evaluate the effect of dietary interventions.

A Review of Nutrients and Compounds, Which Promote or Inhibit Intestinal Iron Absorption: Making a Platform for Dietary Measures That Can Reduce Iron Uptake in Patients with Genetic Haemochromatosis

OBJECTIVE

To provide an overview of nutrients and compounds, which influence human intestinal iron absorption, thereby making a platform for elaboration of dietary recommendations that can reduce iron uptake in patients with genetic haemochromatosis.

DESIGN

Review. Setting. A literature search in PubMed and Google Scholar of papers dealing with iron absorption.

RESULTS

The most important promoters of iron absorption in foods are ascorbic acid, lactic acid (produced by fermentation), meat factors in animal meat, the presence of heme iron, and alcohol which stimulate iron uptake by inhibition of hepcidin expression. The most important inhibitors of iron uptake are phytic acid/phytates, polyphenols/tannins, proteins from soya beans, milk, eggs, and calcium. Oxalic acid/oxalate does not seem to influence iron uptake. Turmeric/curcumin may stimulate iron uptake through a decrease in hepcidin expression and inhibit uptake by complex formation with iron, but the net effect has not been clarified.

CONCLUSIONS

In haemochromatosis, iron absorption is enhanced due to a decreased expression of hepcidin. Dietary modifications that lower iron intake and decrease iron bioavailability may provide additional measures to reduce iron uptake from the foods. This could stimulate the patients' active cooperation in the treatment of their disorder and reduce the number of phlebotomies.

Prevalence of iron deficiency in 62,685 women of seven race/ethnicity groups: The HEIRS Study

BACKGROUND

Few cross-sectional studies report iron deficiency (ID) prevalence in women of different race/ethnicity and ages in US or Canada.

MATERIALS AND METHODS

We evaluated screening observations on women who participated between 2001-2003 in a cross-sectional, primary care-based sample of adults ages ≥25 y whose observations were complete: race/ethnicity; age; transferrin saturation; serum ferritin; and HFE p.C282Y and p.H63D alleles. We defined ID using a stringent criterion: combined transferrin saturation <10% and serum ferritin <33.7 pmol/L (<15 μg/L). We compared ID prevalence in women of different race/ethnicity subgrouped by age and determined associations of p.C282Y and p.H63D to ID overall, and to ID in women ages 25-44 y with or without self-reported pregnancy.

RESULTS

These 62,685 women included 27,079 whites, 17,272 blacks, 8,566 Hispanics, 7,615 Asians, 449 Pacific Islanders, 441 Native Americans, and 1,263 participants of other race/ethnicity. Proportions of women with ID were higher in Hispanics and blacks than whites and Asians. Prevalence of ID was significantly greater in women ages 25-54 y of all race/ethnicity groups than women ages ≥55 y of corresponding race/ethnicity. In women ages ≥55 y, ID prevalence did not differ significantly across race/ethnicity. p.C282Y and p.H63D prevalence did not differ significantly in women with or without ID, regardless of race/ethnicity, age subgroup, or pregnancy.

CONCLUSIONS

ID prevalence was greater in Hispanic and black than white and Asian women ages 25-54 y. p.C282Y and p.H63D prevalence did not differ significantly in women with or without ID, regardless of race/ethnicity, age subgroup, or pregnancy.

Oral Gavage of Ginger Nanoparticle-Derived Lipid Vectors Carrying Dmt1 siRNA Blunts Iron Loading in Murine Hereditary Hemochromatosis

Nanoparticles (NPs) have been utilized to deliver drugs to the intestinal epithelium in vivo. Moreover, NPs derived from edible plants are less toxic than synthetic NPs. Here, we utilized ginger NP-derived lipid vectors (GDLVs) in a proof-of-concept investigation to test the hypothesis that inhibiting expression of divalent metal-ion transporter 1 (Dmt1) would attenuate iron loading in a mouse model of hereditary hemochromatosis (HH). Initial experiments using duodenal epithelial organ cultures from intestine-specific Dmt1 knockout (KO) (Dmt1int/int) mice in the Ussing chamber established that Dmt1 is the only active iron importer during iron-deficiency anemia. Further, when Dmt1int/int mice were crossed with mice lacking the iron-regulatory hormone, hepcidin (Hepc-/-), iron loading was abolished. Hence, intestinal Dmt1 is required for the excessive iron absorption that typifies HH. Additional experiments established a protocol to produce GDLVs carrying functional Dmt1 small interfering RNAs (siRNAs) and to target these gene delivery vehicles to the duodenal epithelium in vivo (by incorporating folic acid [FA]). When FA-GDLVs carrying Dmt1 siRNA were administered to weanling Hepc-/- mice for 16 days, intestinal Dmt1 mRNA expression was attenuated and tissue iron accumulation was blunted. Oral delivery of functional siRNAs by FA-GDLVs is a suitable therapeutic approach to mitigate iron loading in murine HH.

Defining the copper binding aptamotif and aptamer integrated recovery platform (AIRP)

The potential copper binding sites in aptamers have been predicted on the basis of secondary structures and the binding affinity of aptamers with copper. Out of the 4 aptamers (Cu-A1 to Cu-A4) selected by SELEX and examined in the present study, the Cu-A2 aptamer shows the highest binding affinity to copper with the lowest K_D value of 1.83 × 10^-11 M. In order to confirm the binding of copper to the proposed region, the binding affinity was experimentally validated using mutation and deletion analysis. We have confirmed that the high G-C pairing patterns and short stem-interval distance play important roles in copper binding. Aptamer specificity was also verified against diverse heavy metals. We also demonstrate an Aptamer Integrated Recovery Platform (AIRP) to recover copper from acidic mine drainage. AIRP can be easily regenerated at least 20 times without significant deterioration of the retrieval performance. To the best of our knowledge, AIRP is the first demonstration of copper specific recovery using aptamers. This can be scaled up and would have diverse applications in metal contaminated water treatment, recovery and as a potential biosensor for environmental analysis, monitoring, and risk assessment.

Human Nutrition and Genetic Variation

Human genetic variation is a determinant of nutrient efficacy and of tolerances and intolerances and has the potential to influence nutrient intake values (NIVs). Knowledge derived from the comprehensive identification of human genetic variation offers the potential to predict the physiological and pathological consequences of individual genetic differences and prevent and/or manage adverse outcomes through diet. Nutrients and genomes interact reciprocally; genomes confer differences in nutrient utilization, whereas nutrients effectively modify genome expression, stability, and viability. Understanding the interactions that occur among human genes, including all genetic variants thereof, and environmental exposures is enabling the development of genotype-specific nutritional regimens that prevent disease and promote wellness for individuals and populations throughout the life cycle. Genomic technologies may provide new criteria for establishing NIVs. The impact of a gene variant on NIVs will be dependent on its penetrance and prevalence within a population. Recent experiences indicate that few gene variants are anticipated to be sufficiently penetrant to affect average requirement (AR) values to a greater degree than environmental factors. If highly penetrant gene variants are identified that affect nutrient requirements, the prevalence of the variant in that country or region will determine the feasibility and necessity of deriving more than one AR or upper limit (UL) for affected genetic subgroups.

Non-Heme Iron Absorption and Utilization from Typical Whole Chinese Diets in Young Chinese Urban Men Measured by a Double-Labeled Stable Isotope Technique

BACKGROUND

This study was to observe the non-heme iron absorption and biological utilization from typical whole Chinese diets in young Chinese healthy urban men, and to observe if the iron absorption and utilization could be affected by the staple food patterns of Southern and Northern China.

MATERIALS AND METHODS

Twenty-two young urban men aged 18-24 years were recruited and randomly assigned to two groups in which the staple food was rice and steamed buns, respectively. Each subject received 3 meals containing approximately 3.25 mg stable 57FeSO4 (the ratio of 57Fe content in breakfast, lunch and dinner was 1:2:2) daily for 2 consecutive days. In addition, approximately 2.4 mg 58FeSO4 was administered intravenously to each subject at 30-60 min after dinner each day. Blood samples were collected from each subject to measure the enrichment of the 57Fe and 58Fe. Fourteen days after the experimental diet, non-heme iron absorption was assessed by measuring 57Fe incorporation into red blood cells, and absorbed iron utilization was determined according to the red blood cell incorporation of intravenously infused 58Fe SO4.

RESULTS

Non-heme iron intake values overall, and in the rice and steamed buns groups were 12.8 ±2.1, 11.3±1.3 and 14.3±1.5 mg, respectively; the mean 57Fe absorption rates were 11±7%, 13±7%, and 8±4%, respectively; and the mean infused 58Fe utilization rates were 85±8%, 84±6%, and 85±10%, respectively. There was no significantly difference in the iron intakes, and 57Fe absorption and infused 58Fe utilization rates between rice and steamed buns groups (all P>0.05).

CONCLUSION

We present the non-heme iron absorption and utilization rates from typical whole Chinese diets among young Chinese healthy urban men, which was not affected by the representative staple food patterns of Southern and Northern China. This study will provide a basis for the setting of Chinese iron DRIs.

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.

Natural selection on HFE in Asian populations contributes to enhanced non-heme iron absorption

BACKGROUND

HFE, a major regulator of iron (Fe) homeostasis, has been suggested to be under positive selection in both European and Asian populations. While the genetic variant under selection in Europeans (a non-synonymous mutation, C282Y) has been relatively well-studied, the adaptive variant in Asians and its functional consequences are still unknown. Identifying the adaptive HFE variants in Asians will not only elucidate the evolutionary history and the genetic basis of population difference in Fe status, but also assist the future practice of genome-informed dietary recommendation.

RESULTS

Using data from the International HapMap Project, we confirmed the signatures of positive selection on HFE in Asian populations and identified a candidate adaptive haplotype that is common in Asians (52.35-54.71%) but rare in Europeans (5.98%) and Africans (4.35%). The T allele at tag SNP rs9366637 (C/T) captured 95.8% of this Asian-common haplotype. A significantly reduced HFE expression was observed in individuals carrying T/T at rs9366637 compared to C/C and C/T, indicating a possible role of gene regulation in adaptation. We recruited 57 women of Asian descent and measured Fe absorption using stable isotopes in those homozygous at rs9366637. We observed a 22% higher absorption in women homozygous for the Asian-common haplotype (T/T) compared to the control genotype (C/C). Additionally, compared with a group of age-matched Caucasian women, Asian women exhibited significantly elevated Fe absorption.

CONCLUSIONS

Our results indicate parallel adaptation of HFE gene in Europeans and Asians with different genetic variants. Moreover, natural selection on HFE may have contributed to elevated Fe absorption in Asians. This study regarding population differences in Fe homeostasis has significant medical impact as high Fe level has been linked to an increased disease risk of metabolic syndromes.

Non-transferrin-bound iron assay system utilizing a conventional automated analyzer

BACKGROUND

Iron is an essential metal in the body, but its excessive accumulation causes damage in various organs through free radical production. Iron homeostasis is therefore tightly regulated. However, when iron balance collapses, such as in prolonged transfusion, transferrin (Tf) is fully saturated and non-Tf-bound iron (NTBI) appears in the serum. Monitoring serum NTBI levels is therefore crucial in the assessment of the clinical status of patients with iron overload, since NTBI is associated with cellular and organ damage. Several methods for NTBI determination have been reported, but these are extremely complicated and very few laboratories can quantify NTBI at present.

METHODS

We established a novel assay system utilizing automated analyzers that are widely used in clinical laboratories for diagnostic testing. In this assay, NTBI is chelated by nitrilotriacetic acid (NTA), after which the iron is reduced and transferred to nitroso-PSAP, a chromogen.

RESULTS

The assay shows excellent linearity, reproducibility, and compatibility with HPLC, one of the most reliable conventional methods for NTBI quantification.

CONCLUSIONS

Our novel method for NTBI measurement is high-throughput and may be a useful and powerful tool in the study of the physiological and clinical importance of NTBI.

The absorption of iron from whole diets: a systematic review

BACKGROUND

Absorption factors are required to convert physiologic requirements for iron into Dietary Reference Values, but the absorption from single meals cannot be used to estimate dietary iron absorption.

OBJECTIVE

The objective was to conduct a systematic review of iron absorption from whole diets.

DESIGN

A structured search was completed by using the Medline, EMBASE, and Cochrane CENTRAL databases from inception to November 2011. Formal inclusion and exclusion criteria were applied, and data extraction, validity assessment, and meta-analyses were undertaken.

RESULTS

Nineteen studies from the United States, Europe, and Mexico were included. Absorption from diets was higher with an enhancer (standard mean difference: 0.53; 95% CI: 0.21, 0.85; P = 0.001) and was also higher when compared with low-bioavailability diets (standard mean difference: 0.96; 95% CI: 0.51, 1.41; P < 0.0001); however, single inhibitors did not reduce absorption (possibly because of the limited number of studies and participants and their heterogeneity). A regression equation to calculate iron absorption was derived by pooling data for iron status (serum and plasma ferritin) and dietary enhancers and inhibitors from 58 individuals (all from US studies): log[nonheme-iron absorption, %] = -0.73 log[ferritin, μg/L] + 0.11 [modifier] + 1.82. In individuals with serum ferritin concentrations from 6 to 80 μg/L, predicted absorption ranged from 2.1% to 23.0%.

CONCLUSIONS

Large variations were observed in mean nonheme-iron absorption (0.7-22.9%) between studies, which depended on iron status (diet had a greater effect at low serum and plasma ferritin concentrations) and dietary enhancers and inhibitors. Iron absorption was predicted from serum ferritin concentrations and dietary modifiers by using a regression equation. Extrapolation of these findings to developing countries and to men and women of different ages will require additional high-quality controlled trials.

Iron metabolism: microbes, mouse, and man

Recent advances in research on iron metabolism have revealed the identity of a number of genes, signal transduction pathways, and proteins involved in iron regulation in mammals. The emerging paradigm is a coordination of homeostasis within a network of classical iron metabolic pathways and other cellular processes such as cell differentiation, growth, inflammation, immunity, and a host of physiologic and pathologic conditions. Iron, immunity, and infection are intricately linked and their regulation is fundamental to the survival of mammals. The mutual dependence on iron by the host and invading pathogenic organisms elicits competition for the element during infection. While the host maintains mechanisms to utilize iron for its own metabolism exclusively, pathogenic organisms are armed with a myriad of strategies to circumvent these measures. This review explores iron metabolism in mammalian host, defense mechanisms against pathogenic microbes and the competitive devices of microbes for access to iron.

Iron bioavailability and dietary reference values

Iron differs from other minerals because iron balance in the human body is regulated by absorption only because there is no physiologic mechanism for excretion. On the basis of intake data and isotope studies, iron bioavailability has been estimated to be in the range of 14-18% for mixed diets and 5-12% for vegetarian diets in subjects with no iron stores, and these values have been used to generate dietary reference values for all population groups. Dietary factors that influence iron absorption, such as phytate, polyphenols, calcium, ascorbic acid, and muscle tissue, have been shown repeatedly to influence iron absorption in single-meal isotope studies, whereas in multimeal studies with a varied diet and multiple inhibitors and enhancers, the effect of single components has been, as expected, more modest. The importance of fortification iron and food additives such as erythorbic acid on iron bioavailability from a mixed diet needs clarification. The influence of vitamin A, carotenoids, and nondigestible carbohydrates on iron absorption and the nature of the "meat factor" remain unresolved. The iron status of the individual and other host factors, such as obesity, play a key role in iron bioavailability, and iron status generally has a greater effect than diet composition. It would therefore be timely to develop a range of iron bioavailability factors based not only on diet composition but also on subject characteristics, such as iron status and prevalence of obesity.

Nonheme-iron absorption in first-degree relatives is highly correlated: a stable-isotope study in mother-child pairs

BACKGROUND

Iron absorption in humans is highly variable even after iron status and dietary components that influence iron absorption are controlled for. Inherited factors may help explain this variance.

OBJECTIVE

Our objective was to compare nonheme-iron absorption from a noninhibitory, stable-isotope-labeled test meal in preschool-aged children and their mothers.

DESIGN

We provided 72 test meals based on degermed maize flour and milk powder and fortified with [(57)Fe]ferrous fumarate or [(58)Fe]ferrous sulfate to healthy Mexican preschool children [n = 18; mean (+/-SD) age: 3.6 +/- 1.0 y] and their mothers [n = 18; mean (+/-SD) age: 28.0 +/- 5.2 y]. Iron absorption was calculated on the basis of incorporation of isotopes into erythrocytes after 14 d and was adjusted for differences in iron status.

RESULTS

There was a wide variation in iron absorption from the test meals: in the mothers and children, the median fractional absorption of ferrous sulfate was 22.55% (range: 1.65-54.83%) and 5.51% (range: 2.23-17.20%), respectively (P < 0.0001). After adjustment for serum ferritin, the significant difference in absorption between mothers and their children disappeared. Despite this broad range of iron absorption, corrected fractional iron absorption from the ferrous fumarate-fortified (r(2) = 0.582) and the ferrous sulfate-fortified test meals (r(2) = 0.557) was strongly correlated in mothers and their children (P < 0.0001). There was a striking positive correlation between the mean corrected fractional iron absorption from both test meals in mothers and their children (r(2) = 0.782, P < 0.0001). In regression analyses that included age, sex, and hemoglobin, the only significant predictor of corrected fractional iron absorption in children was corrected fractional iron absorption in their mothers (standardized beta = 0.884, P < 0.001).

CONCLUSIONS

Nonheme-iron absorption exhibits a strong familial tendency. After differences in meal matrix and serum ferritin are accounted for, these data suggest that inheritance and/or shared environmental factors explain most of the variance in dietary iron absorption.

Body iron excretion by healthy men and women

BACKGROUND

Iron excretion measured by isotope dilution has been a primary basis for the factorial derivation of recommendations for iron intake, but the results have been available for men only.

OBJECTIVE

The objective of this study was to confirm iron excretion measurements in healthy men and extend them to women.

DESIGN

The turnover rate of 55Fe that had been administered > or =1 y earlier was determined from blood sampled semiannually for up to 3 y from 53 subjects in the community. Body iron was determined from hemoglobin, serum ferritin, and transferrin receptor. Complete menstrual collections were obtained from 13 women.

RESULTS

The total median (range) iron excretion was 1.18 (0.11-2.07) mg/d for 29 men, 1.58 (0.65-4.88) mg/d for 19 menstruating women, and 0.99 (0.86-1.57) for 5 postmenopausal women. When hormonal contraceptive users were omitted, the median for 15 menstruating women increased to 1.66 mg/d. The distribution of iron excretion was normal for the men and postmenopausal women and was highly skewed for the menstruating women; menstrual iron accounted for 90% of the variation. Iron excretion was not strongly related to body weight. Body iron in menstruating women decreased somewhat (by 4.6%) in the men and tended to increase (by 1.5%) during the study.

CONCLUSIONS

The results extend direct iron excretion measurements in men to include similar measurements in women. The results emphasize the wide range of iron excretion in humans, which results in a 40-fold range of requirements for absorbed iron. This trial was registered at clinicaltrials.gov as NCT00755105.

Haemochromatosis HFE gene polymorphisms as potential modifiers of hereditary nonpolyposis colorectal cancer risk and onset age

Hereditary nonpolyposis colorectal cancer (HNPCC) is characterized by germline mutations in DNA mismatch repair genes; however, variation in disease expression suggests that there are potential modifying factors. Polymorphisms of the HFE gene, which cause the iron overload disorder hereditary haemochromatosis, have been proposed as potential risk factors for the development of colorectal cancer (CRC). To understand the relationship between HNPCC disease phenotype and polymorphisms of the HFE gene, a total of 362 individuals from Australia and Poland with confirmed causative MMR gene mutations were genotyped for the HFE C282Y and H63D polymorphisms. A significantly increased risk of developing CRC was observed for H63D homozygotes when compared with combined wild-type homozygotes and heterozygotes (hazard ratio = 2.93, p = 0.007). Evidence for earlier CRC onset was also observed in H63D homozygotes with a median age of onset 6 years earlier than wild type or heterozygous participants (44 vs. 50 years of age). This effect was significant by all tests used (log-rank test p = 0.026, Wilcoxon p = 0.044, Tarone-Ware p = 0.035). No association was identified for heterozygosity of either polymorphism and limitations on power-prevented investigation of C282Y homozygosity or compound C282Y/H63D heterozygosity. In the Australian sample only, women had a significantly reduced risk of developing CRC when compared with men (hazard ratio = 0.58, p = 0.012) independent of HFE genotype for either single nucleotide polymorphisms. In conclusion, homozygosity for the HFE H63D polymorphism seems to be a genetic modifier of disease expression in HNPCC. Understanding the mechanisms by which HFE interrelates with colorectal malignancies could lead to reduction of disease risk in HNPCC.

Genetic and epigenetic contributions to human nutrition and health: managing genome-diet interactions

The Institute of Medicine recently convened a workshop to review the state of the various domains of nutritional genomics research and policy and to provide guidance for further development and translation of this knowledge into nutrition practice and policy. Nutritional genomics holds the promise to revolutionize both clinical and public health nutrition practice and facilitate the establishment of (a) genome-informed nutrient and food-based dietary guidelines for disease prevention and healthful aging, (b) individualized medical nutrition therapy for disease management, and (c) better targeted public health nutrition interventions (including micronutrient fortification and supplementation) that maximize benefit and minimize adverse outcomes within genetically diverse human populations. As the field of nutritional genomics matures, which will include filling fundamental gaps in knowledge of nutrient-genome interactions in health and disease and demonstrating the potential benefits of customizing nutrition prescriptions based on genetics, registered dietitians will be faced with the opportunity of making genetically driven dietary recommendations aimed at improving human health.

Blood loss is a stronger predictor of iron status in men than C282Y heterozygosity or diet

OBJECTIVE

To determine the relative importance of HFE gene, diet, lifestyle, and blood loss characteristics for predicting iron status in a sample of men aged 40 years or over.

DESIGN

Iron status (serum ferritin, transferrin saturation, soluble transferrin receptor) was measured in 44 C282Y heterozygote and 85 age- and BMI-matched wildtype men aged 40 years or over. Dietary intake of iron (total, heme and non-heme), and components known to influence iron bioavailability, was determined using a validated Meal-Based Intake Assessment Tool. Information on lifestyle and blood loss was obtained by questionnaire. Height and weight were measured to determine Quetelet's body mass index. Linear mixed models were used to determine the extent to which these variables predicted iron status.

RESULTS

C282Y heterozygosity was associated with 17% higher transferrin saturation (95% CI: 6%, 29%) but no difference in serum ferritin or soluble transferrin receptor concentrations. Blood donation was negatively associated with transferrin saturation (-13% (- 3%, -22%)) and serum ferritin (-58% (-44%, -68%)), and had a marginally significant positive association with soluble transferrin receptor concentration. Self-reported fecal blood loss was negatively associated with serum ferritin concentration (-35% (-54%, -7%)). Alcohol was the only dietary variable associated with iron status and was associated with all three of the iron status indices. Serum ferritin concentration was positively associated with body mass index (10% per unit increase (6%, 15%)).

CONCLUSIONS

Blood loss was a stronger predictor of iron status than either C282Y heterozygosity or diet in this population of men aged 40 years and over.

HLA haplotype map of river valley populations with hemochromatosis traced through five centuries in Central Sweden

BACKGROUND

The hemochromatosis mutation, C282Y of the HFE gene, seems to have originated from a single event which once occurred in a person living in the north west of Europe carrying human leukocyte antigen (HLA)-A3-B7. In descendants of this ancestor also other haplotypes appear probably caused by local recombinations and founder effects. The background of these associations is unknown. Isolated river valley populations may be fruitful for the mapping of genetic disorders such as hemochromatosis. In this study, we try to test this hypothesis in a study from central Sweden where the haplotyope A1-B8 was common.

METHODS

HLA haplotypes and HFE mutations were studied in hemochromatosis patients with present or past parental origin in a sparsely populated (1/km(2)) rural district (n = 8366 in the year of 2005), in central Sweden. Pedigrees were constructed from the Swedish church book registry. Extended haplotypes were studied to evaluate origin of recombinations.

RESULTS

There were 87 original probands, 36 females and 51 males identified during 30 yr, of whom 86% carried C282Y/C282Y and 14% C282Y/H63D. Of 32 different HLA haplotypes A1-B8 was the most common (34%), followed by A3-B7 (16%), both in strong linkage disequilibrium with controls, (P < 0.001). Twenty-nine different families with A1-B8 had a common founder origin 15 generations ago in small bottleneck populations of the late 16th century. A second A1-B8 founder born 1655 was of Norwegian origin. Most of the A3 carriers (n = 26) had a common founder origin 16 generations ago in an even smaller nearby river valley. A fourth founder family carrying HLA-A2 seems to have originated from a recombination along the descendant lines from the A3 ancestor supported by extended haplotype studies. A1-haplotypes with alleles at the B locus different from B8 had a similar recombination origin as HLA-A2 alleles and a common founder origin 11 generations ago. The intergenerational time interval averaged 35.5 +/- 7.9 yr in men and 31.9 +/- 5.9 in females.

CONCLUSIONS

River valley populations may contain HLA haplotypes reflecting their demographic history. This study has demonstrated that the resistance against recombinations between HLA-A and HFE make HLA haplotypes excellent markers for population movements. Founder effects and genetic drift from bottleneck populations (surviving the plague?) may explain the commonness of the mutation in central Scandinavia. The intergenerational time difference >30 yr was greater than expected and means that the age of the original mutation may be underestimated.

Post-prandial iron absorption in humans: comparison between HFE genotypes and iron deficiency anaemia

BACKGROUND & AIMS

Measurement of serum iron increase after ingestion of a meal could be an efficient method of comparing post-prandial iron absorption between groups of individuals. We determined whether the rise in post-prandial serum iron is increased in fully treated patients with hereditary haemochromatosis (HFE C282Y+/+; HH) compared to iron deficiency anaemia (IDA), iron-replete heterozygous subjects (HFE C282Y+/-) and iron-replete controls (HFE C282Y-/-).

METHODS

Serum iron increase was measured over 4h after a meal containing 13.1 mg non-haem iron.

RESULTS

Post-prandial increase in serum iron was similar in treated HH versus IDA (P=0.54), but greater than control subjects (P<0.0001). In five HH patients, using (58)Fe as a tracer, the rate of iron absorption was increased (P<0.05) and serum non-transferrin bound iron showed a tendency to increase (P=0.06). Serum iron curves did not differ for heterozygous subjects and controls (P=0.65).

CONCLUSIONS

Using the serum iron method we found a comparable increase in post-prandial iron absorption in treated HH and IDA compared with controls. While post-prandial iron absorption in the group heterozygous for the C282Y mutation was modestly increased relative to controls, this difference was not statistically significant.

Iron absorption by healthy women is not associated with either serum or urinary prohepcidin

BACKGROUND

Although hepcidin is proposed as a regulator of iron absorption, this has not been assessed in humans.

OBJECTIVE

Our objective was to assess the relation between serum or urinary prohepcidin and iron absorption in healthy premenopausal women.

DESIGN

The subjects were 28 healthy women aged 22-51 y with normal hemoglobin concentrations (120-152 g/L). Absorption of 0.5 mg Fe with 0.2 microCi 59Fe tracer, both as FeSO4, was measured by whole-body scintillation counting 13 d after oral administration. Fasting blood and urine samples were collected the day of and 16 wk after the absorption measurement. Serum and urinary prohepcidin concentrations were measured by an enzyme-linked immunosorbent assay by using an antibody against amino acid residues 28-47 of the proregion.

RESULTS

Mean (+/-SD) iron absorption was 36 +/- 19% (range: 4-81%), and serum ferritin (geometric x) was 27 microg/L (range: 4-122 microg/L), as commonly observed in healthy premenopausal women. Serum prohepcidin was 196 microg/L (range: 99-376 microg/L) and, in contrast with urinary prohepcidin, was relatively consistent for the women between 0 and 16 wk. Serum prohepcidin correlated directly with serum ferritin (R2 = 0.28, P < 0.01) but was unrelated to 59Fe absorption, in contrast to serum ferritin (R2 = 0.33, P < 0.01).

CONCLUSIONS

Serum prohepcidin concentrations were relatively stable within subjects and correlated with serum ferritin. However, unlike serum ferritin, neither serum nor urinary prohepcidin concentrations were related to iron absorption in healthy women.

Genetic diversity and genetic burden in humans

We discuss categories of genetic diversity in humans. Neutral diversity, population differences in frequencies of genetic markers that we think are invisible to natural selection, provides a passive record of population history but is otherwise of little interest in human biology. Genetic variation related to disease can be separated into mutational noise and variation due to selection, either ongoing selection else effects of a past environment. We distinguish consequences of genetic diversity for fitness, relevant to evolution, and consequences for well-being, relevant to medicine and public health. We call genetic variation that causes impairment of health or well-being of individual humans "apparent genetic burden" and variation that has effects on fitness but not well-being "unapparent genetic burden". We use "burden" to distinguish these notions from the classical concept of "genetic load" that refers to effects on population fitness, a concept formulated by Morton et al. [Morton, N.E., Crow, J.F., Muller, H.J., 1956. An estimate of the mutational damage in man from data on consanguineous marriages. Proc. Natl. Acad. Sci. U.S.A. 42, 855-863]. We distinguish adapted genes and adapted genotypes: an adapted gene is a gene that increases fitness of its bearer either in heterozygous or homozygous state or both, while an adapted genotype is a genotype that increases fitness of its bearer but is not transmitted intact to future generations. Balanced polymorphisms in which the heterozygote is superior in fitness may generate most adapted genotypes. In the face of major rapid environmental change adapted genotypes appear first but over time they are replaced by adapted genes. The presence of adapted genotypes is a good indication of recent environmental change: for example, there are apparently many polymorphisms in domestic animals of this nature, responses to domestication, and many fewer in wild animals (and in humans).

HFE genotypes and dietary heme iron: no evidence of strong gene-nutrient interaction on serum ferritin concentrations in middle-aged women

BACKGROUND AND AIM

Hereditary hemochromatosis (HH) is a disorder characterized by inappropriately high intestinal iron absorption. In populations of Northern European descent, HH is most commonly caused by mutations (C282Y/H63D) in the HFE gene.

METHODS AND RESULTS

We investigated the effects of dietary heme iron intake and HFE mutations on serum ferritin concentrations in a population-based random sample of 1611 women aged >50 years using analysis of covariance (ANCOVA). Higher heme iron intake was associated with significantly higher serum ferritin concentrations (P(trend) < 0.001). Also, women with the compound or C282Y homozygous genotype had significantly higher serum ferritin concentrations (geometric mean 115.2 microg/L (95% CI 81.4-162.9 microg/L) than women carrying normal alleles (geometric mean 76.6 microg/L (95% CI 72.5-80.9 microg/L). We observed the highest serum ferritin concentrations among postmenopausal women who are compound heterozygous or C282Y homozygous, and who consume relatively high amounts of heme iron (geometric mean 183.9 microg/L (95% CI 97.2-347.8 microg/L).

CONCLUSIONS

Even when there are currently no clinical signs, women with the compound or C282Y homozygous genotype may still be at risk for developing iron overload sometime after menopause.

HFE genetic variability, body iron stores, and the risk of type 2 diabetes in U.S. women

To determine whether the HFE gene variants H63D and C282Y are associated with body iron stores and the risk of type 2 diabetes, we conducted a nested case-control study of 714 incident cases of type 2 diabetes and 1,120 matching control subjects in a prospective cohort, the Nurses' Health Study. In both healthy control and diabetic case subjects, H63D homozygosity, C282Y, and the compound heterozygotes were associated with significantly higher levels of plasma ferritin and significantly lower ratios of transferrin receptors to ferritin. Such effects were independent of age, BMI, and lifestyle factors. Overall, there were no significant differences in genotypes of H63D and C282Y between the case and control subjects. A meta-analysis of 4,245 case and 5,982 control subjects indicated a null association of C282Y with diabetes risk, whereas carriers of H63D or the compound heterozygotes had marginally increased risk (odds ratio [OR] 1.11 [95% CI 1.00-1.25] and 1.60 [0.99-2.60], respectively). In addition, we found a significant interaction between HFE variants and heme iron intake (P for interaction = 0.029). The ORs of type 2 diabetes across increasing quartiles of heme iron were 1.00, 1.21 (0.72-2.01), 1.72 (1.03-2.88), and 1.49 (0.91-2.46) among the participants with either the H63D or C282Y variant, whereas the ORs were 1.00, 0.71 (0.49-1.05), 1.12 (0.76-1.66), and 0.96 (0.65-1.42) among those with wild-type genotypes. Our data indicate significant effects of H63D and C282Y on body iron stores and suggest a potential interaction between HFE genotypes and heme iron intake in relation to the risk of type 2 diabetes.

Iron absorption in male C282Y heterozygotes

BACKGROUND

The suggestion that carriers of the HFE C282Y mutation absorb nonheme iron more efficiently than do carriers of the wild type has public health implications for countries where the C282Y mutation is common and foods are fortified with iron.

OBJECTIVE

We investigated the effect of C282Y heterozygosity on nonheme-iron absorption from a diet high in bioavailable iron and from iron-fortified cereals.

DESIGN

The subjects were recruited from a parallel study investigating the relation between HFE mutations, habitual diet, and iron status. Iron absorption was measured in 15 wild-type carriers and 15 C282Y heterozygotes aged >/=40 y. Each subject consumed 3 meals of high iron bioavailability (labeled with Fe-57) for 2 d and 2 meals with fortified cereal products (labeled with Fe-54) for the next 3 d. Iron absorption was measured from isotope incorporation into red blood cells 14 d after the last labeled meal and was corrected for utilization of absorbed iron by means of an intravenous infusion of Fe-58.

RESULTS

Absorption of Fe-57 with the high-iron-bioavailability diet was 6.8 +/- 6.8% (0.6 +/- 0.6 mg/d) in the wild-type carriers and 7.6 +/- 3.2% (0.7 +/- 0.3 mg/d) in the C282Y heterozygotes. Absorption of Fe-54 with cereal products was 4.9 +/- 2.0% (0.7 +/- 0.3 mg/d) in the wild-type carriers and 5.3 +/- 1.3% (0.8 +/- 0.2 mg/d) in the C282Y heterozygotes.

CONCLUSIONS

There was no overall significant difference between C282Y heterozygotes and wild-type men in iron absorption from either dietary nonheme iron or fortified cereal products.