Research ArticleHepcidin, transferrin (exon 7), and hemochromatosis genotyping suggests that haplotype block analysis is the best strategy for predicting iron deficiency phenotype in women☆
Introduction
The effects of diet on health and disease prevention would prove much more effective if dietary recommendations were based on genotype. Most genes have small sequence differences or polymorphisms that may affect how well a protein works and how it interacts with other proteins or substrates. Single-nucleotide polymorphisms (SNPs) are the most common form of DNA sequence variation and are useful polymorphic markers for investigating genes. Haplotypes are sets of SNP alleles along a region of a chromosome. Analysis of haplotypes or haplotype blocks [1] forms part of a recent strategy to draw associations between disease, genes, and nutrients.
Iron deficiency anemia is only part of a highly prevalent iron deficiency syndrome. Little is known about the genetic basis of non–diet-related iron deficiency. The genetic contribution to the interindividual differences of iron reserves in women outweighs the relatively small effect of iron loss through menstruation and repeated pregnancies [2]. A polymorphism in exon 7 (G277S) of the transferrin (Tf) gene, which corresponds to the Tf electrophoretic C3 variant, has been associated with a significant reduction in total iron-binding capacity and a higher mean Tf saturation, predisposing menstruating women to iron deficiency anemia [3]. The highest frequency of this variant is found in the white population (frequency of 0.0634; 111 of 1752 alleles) [3]. However, Aisen [4] constructed the mutation in a human Tf expression vector and observed that mutant and native proteins were equally efficient at donating iron. Accordingly, no relationship was found between Tf concentration, iron status, and the G277S variant in pregnant women [5]. The G277S Tf mutation did not affect iron absorption in iron-deficient women more than the wild genotype [6]. With this finding in mind, the role of G277S polymorphisms in iron deficiency anemia also needs to be clarified. The G277S mutation may be associated with other Tf mutations and/or other polymorphisms located in other genes.
It is widely known that hemochromatosis (HFE) and hepcidin (HAMP) genes are involved in iron metabolism. HFE mutations C282Y and H63D are responsible for iron overload [7], [8]. However, their role in iron deficiency remains controversial. According to Beutler [9], the prevalence of nonanemic iron deficiency in a large cohort of patients with HFE mutations was significantly lower in female carriers of the C282Y mutation than in those with wild-type HFE. However, prevalence of iron deficiency anemia did not differ significantly among genotypes. Datz et al [10] suggest that the C282Y mutation may protect against iron deficiency in young women. C282Y-heterozygous women showed significantly higher values for hemoglobin (Hb), serum iron, and Tf saturation than those homozygous for the wild-type allele, but there was no significant difference in the prevalence of iron deficiency anemia or iron depletion between these groups. Similarly, Rossi et al [11] found significantly higher mean hemoglobin levels among C282Y/H63D compound heterozygotes than among wild-type homozygotes. These authors reported no significant difference between genotypes with regard to the prevalence of subjects with iron depletion (defined as ferritin [Ft] <20 μg or ferritin <12 μg/L and a Tf saturation <15%). The H63D mutation is relevant in certain geographical areas, such as Spain [12], [13], [14], but its frequency and clinical penetrance has been studied to less extent than C282Y. None of these studies have looked into the possible association between the C282Y and H63D mutations and other mutations in iron metabolism proteins.
The HAMP gene codes for hepcidin, which plays an essential role in iron homeostasis [15]. This peptide is a novel, hepatic, antimicrobial hormone that could provide the link between iron stores and intestinal absorption [16]. At the molecular level, it seems to be the key systemic regulator of iron absorption [17]. In mice, the predominant issue in regulating the HAMP gene appears to be anemia [18]. Given that this gene plays such an important role in iron homeostasis, its mutations are likely to produce distinctive, iron-related phenotypes [19], [20].
The study of Tf/HFE/HAMP haplotypes may reveal strong associations between the iron deficiency phenotype and genotype. The aim of this work is to determine HAMP, Tf (exon 7), and HFE mutations and their possible value in predicting the iron deficiency phenotype in women.
Section snippets
Subjects
Volunteer recruitment was carried out through announcements on the Complutense University campus and short talks about the study between lectures. One hundred sixty-two 18- to 45-year-old, nonpregnant, nonsmoking, white, menstruating women were recruited. Volunteers had not been treated with iron during the previous 12 months. All subjects underwent a prestudy screening, which included a blood test and health questionnaire. This study was approved by the ethics committee of the Clínica Puerta
Results
In accordance with the hemoglobin (g/dL) and ferritin (μg/L) values obtained among the 162 subjects, 63 were iron-sufficient (Hb ≥12, Ft ≥20), 77 were iron-deficient (Hb ≥12 and Ft <20 or Hb <12 and Ft ≥20) and 22 were iron-deficient anemic (Hb <12 and Ft <20). Table 1 contains the hematologic and biochemical parameter data of the 3 iron status groups. Values for the other iron status indicators examined (total iron-binding capacity, Tf saturation, hematocrit, and mean corpuscular volume) were
Discussion
Percentages of iron-deficient, menstruating white women within the G277G Tf genotype are comparable to those described by Lee et al [3], who worked with a larger group of white women (n = 1511) and obtained a higher prevalence of iron deficiency in menstruating white women with G277S/G277S and G277S/G277G genotypes than in wild-type subjects. In concordance with their findings, we obtained a higher prevalence of iron deficiency in women with genotype G277S/G277G (18.7%) compared to those of the
Acknowledgment
The authors wish to thank the volunteers who took part in the study and Laura Barrios for the statistical analysis. This research is part of the scientific activities included in the Framework Agreement between the Spanish Research Council, the Complutense University of Madrid, and the General Direction of Public Health of the Community of Madrid, Spain.
References (29)
- et al.
Nutrigenomics, proteomics, metabolomics and the practice of dietetics
J Am Diet Assoc
(2006) Iron storage disease: facts, fiction and progress
Blood Cells Mol Dis
(2007)Understanding iron homeostasis through genetic analysis of hemochromatosis and related disorders
Blood
(2005)- et al.
The solution structure of human hepcidin, a peptide hormone with antimicrobial activity that is involved in iron uptake and hereditary hemochromatosis
J Biol Chem
(2002) - et al.
The orchestration of body iron intake: how and where do enterocytes receive their cues?
Blood Cells Mol Diseases
(2003) - et al.
Molecular characterization of a case of atransferrinemia
Blood
(2000) - et al.
Molecular characterization of a third case of human atransferrinemia
Blood
(2004) - et al.
Assessing iron status of a population
Am J Clin Nutr
(1979) - et al.
Relative importance of female-specific and non–female-specific effects on variation in iron stores between women
Br J Haematol
(2003) - et al.
Human transferrin G277S mutation: a risk factor for iron deficiency anaemia
Br J Haematol
(2001)
The G277S mutation in transferrin does not disturb function
Br J Haematol
Human transferrin G277S mutation and iron deficiency in pregnancy
Br J Haematol
The G277S transferrin mutation does not affect iron absorption in iron deficient women
Eur J Nutr
Haematological effects of the C282Y HFE mutation in homozygous and heterozygous states among subjects of northern and southern European ancestry
Br J Haematol
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This study was funded by the European Commission (Brussels, Belgium), Marie Curie European Reintegration Grants (MERG-CT-2003-506368) and the Spanish government (AGL 2002-04411-C02-02 ALI). Santiago Navas-Carretero received a fellowship grant from the Comunidad de Madrid and European Social Funds.