Mutations in the hemochromatosis gene (HFE) and multiple sclerosis

Lack of association between C282Y and H63D polymorphisms in the hemochromatosis gene and risk of multiple sclerosis: A meta-analysis

Increasing evidence supports the potential role of iron metabolism in multiple sclerosis (MS). Previous studies examining the association between polymorphisms of the hemochromatosis gene (HFE) and susceptibility to MS have yielded inconsistent results. In the present study, a meta-analysis of 7 studies was performed conducted in populations of Caucasian origin using the Comprehensive Meta-analysis 3.0 software. The strength of association between the C282Y and H63D polymorphisms in HFE and MS risk was estimated by odds ratios with 95% confidence intervals. Cochran's Q statistic and I² tests were applied to quantify heterogeneity between studies. An Egger's test was used to estimate publication bias. The C282Y and H63D polymorphisms had no significant association with increased MS risk (all P≥0.05) in the following genetic comparison models: Dominant model (YY + CY vs. CC or DD + HD vs. HH) and allele contrast (Y vs. C or D vs. H). No apparent publication bias or significant heterogeneity was found between studies. These results suggest that the HFE polymorphisms C282Y and H63D are not associated with susceptibility to MS in populations of Caucasian origin. Further studies should be performed in a larger series of MS patients to evaluate the contribution of HFE and other genetic variants associated with iron regulation in the development and progression of MS.

The roles of iron and HFE genotype in neurological diseases

Iron accumulation is a recurring pathological phenomenon in many neurological diseases including Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, and others. Iron is essential for normal development and functions of the brain; however, excess redox-active iron can also lead to oxidative damage and cell death. Especially for terminally differentiated cells like neurons, regulation of reactive oxygen species is critical for cell viability. As a result, cellular iron level is tightly regulated. Although iron accumulation related to neurological diseases has been well documented, the pathoetiological contributions of the homeostatic iron regulator (HFE), which controls cellular iron uptake, is less understood. Furthermore, a common HFE variant, H63D HFE, has been identified as a modifier of multiple neurological diseases. This review will discuss the roles of iron and HFE in the brain as well as their impact on various disease processes.

Gene-gene interactions among coding genes of iron-homeostasis proteins and APOE-alleles in cognitive impairment diseases

Cognitive impairments of different aetiology share alterations in iron and lipid homeostasis with mutual relationships. Since iron and cholesterol accumulation impact on neurodegenerative disease, the associated gene variants are appealing candidate targets for risk and disease progression assessment. In this light, we explored the role of common single nucleotide polymorphisms (SNPs) in the main iron homeostasis genes and in the main lipoprotein transporter gene (APOE) in a cohort of 765 patients with dementia of different origin: Alzheimer’s disease (AD) n = 276; vascular dementia (VaD), n = 255; mild cognitive impairment (MCI), n = 234; and in normal controls (n = 1086). In details, four genes of iron homeostasis (Hemochromatosis (HFE: C282Y, H63D), Ferroportin (FPN1: -8CG), Hepcidin (HAMP: -582AG), Transferrin (TF: P570S)), and the three major alleles of APOE (APOE2, APOE3, APOE4) were analyzed to explore causative interactions and synergies. In single analysis, HFE 282Y allele yielded a 3-fold risk reduction in the whole cohort of patients (P<0.0001), confirmed in AD and VaD, reaching a 5-fold risk reduction in MCI (P = 0.0019). The other iron SNPs slightly associated with risk reduction whereas APOE4 allele resulted in increased risk, reaching more than 7-fold increased risk in AD homozygotes (P = 0.001), confirmed to a lower extent in VaD and MCI (P = 0.038 and P = 0.013 respectively) as well as in the whole group (P<0.0001). Comparisons of Mini Mental State Examination (MMSE) among AD showed appreciable lowering in APOE4 carriers (P = 0.038), confirmed in the whole cohort of patients (P = 0.018). In interaction analysis, the HFE 282Y allele completely extinguished the APOE4 allele associated risk. Conversely, the coexistence in patients of a substantial number of iron SNPs accrued the APOE4 detrimental effect on MMSE. Overall, the analysis highlighted how a specific iron-allele burden, defined as different combinations of iron gene variants, might have different effects on cognitive impairment and might modulate the effects of established genetic risk factors such as APOE4. Our results suggest that established genetic risk factors might be affected by specific genetic backgrounds, making patients differently suited to manage iron accumulation adding new genetic insights in neurodegeneration. The recently recognized interconnections between iron and lipids, suggest that these pathways might share more than expected. We therefore extended to additional iron gene variants the newly proposed influencing mechanisms that HFE gene has on cholesterol metabolism. Our results have a strong translational potential promoting new pharmacogenetics studies on therapeutic target identification aimed at optimally tuning brain iron levels.

Iron-related gene variants and brain iron in multiple sclerosis and healthy individuals

Brain iron homeostasis is known to be disturbed in multiple sclerosis (MS), yet little is known about the association of common gene variants linked to iron regulation and pathological tissue changes in the brain. In this study, we investigated the association of genetic determinants linked to iron regulation with deep gray matter (GM) magnetic susceptibility in both healthy controls (HC) and MS patients. Four hundred (400) patients with MS and 150 age- and sex-matched HCs were enrolled and obtained 3 T MRI examination. Three (3) single nucleotide polymorphisms (SNPs) associated with iron regulation were genotyped: two SNPs in the human hereditary hemochromatosis protein gene HFE: rs1800562 (C282Y mutation) and rs1799945 (H63D mutation), as well as the rs1049296 SNP in the transferrin gene (C2 mutation). The effects of disease and genetic status were studied using quantitative susceptibility mapping (QSM) voxel-based analysis (VBA) and region-of-interest (ROI) analysis of the deep GM. The general linear model framework was used to compare groups. Analyses were corrected for age and sex, and adjusted for false discovery rate. We found moderate increases in susceptibility in the right putamen of participants with the C282Y (+ 6.1 ppb) and H63D (+ 6.9 ppb) gene variants vs. non-carriers, as well as a decrease in thalamic susceptibility of progressive MS patients with the C282Y mutation (left: − 5.3 ppb, right: − 6.7 ppb, p < 0.05). Female MS patients had lower susceptibility in the caudate (− 6.0 ppb) and putamen (left: − 3.9 ppb, right: − 4.6 ppb) than men, but only when they had a wild-type allele (p < 0.05). Iron-gene linked increases in putamen susceptibility (in HC and relapsing remitting MS) and decreases in thalamus susceptibility (in progressive MS), coupled with apparent sex interactions, indicate that brain iron in healthy and disease states may be influenced by genetic factors.

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Magnetic susceptibility and common gene variants linked to iron were investigated.

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The C282Y and H63D alleles were associated with putamen and thalamus susceptibility changes.

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Dependent on allele status, men and women differed in deep GM susceptibility in MS.

The hemochromatosis protein HFE 20 years later: An emerging role in antigen presentation and in the immune system

Introduction

Since its discovery, the hemochromatosis protein HFE has been primarily defined by its role in iron metabolism and homeostasis, and its involvement in the genetic disease termed hereditary hemochromatosis (HH). While HH patients are typically afflicted by dysregulated iron levels, many are also affected by several immune defects and increased incidence of autoimmune diseases that have thereby implicated HFE in the immune response. Growing evidence has supported an immunological role for HFE with recent studies describing HFE specifically as it relates to MHC I antigen presentation.

Methods/Results

Here, we present a comprehensive overview of the relationship between iron metabolism, HFE, and the immune system to better understand the origin and cause of immune defects in HH patients. We further describe the role of HFE in MHC I antigen presentation and its potential to impair autoimmune responses in homeostatic conditions, a mechanism which may be exploited by tumors to evade immune surveillance.

Conclusion

Overall, this increased understanding of the role of HFE in the immune response sets the stage for better treatment and management of HH and other iron‐related diseases, as well as of the immune defects related to this condition.

HFE p.C282Y heterozygosity is associated with earlier disease onset in Friedreich ataxia

BACKGROUND

Friedreich ataxia (FRDA) generally results from reduced frataxin, a mitochondrial protein involved in iron metabolism. We assessed whether HFE p.C282Y and/or p.H63D heterozygosity modifies age at disease onset or disease severity in individuals with FRDA.

METHODS

One hundred seventy individuals with FRDA were assessed for the association of HFE p.C282Y and p.H63D with (1) age at disease onset and (2) Friedreich Ataxia Rating Scale (FARS) score.

RESULTS

After adjusting for the smaller FXN GAA repeat size and sex, individuals with FRDA and heterozygous for p.C282Y had disease onset on average 3.72 years earlier than those homozygous for the wild-type amino acid (P = 0.02). Neither mutation affected disease severity as measured by FARS.

CONCLUSIONS

It is hypothesized that the association between p.C282Y heterozygosity and an earlier age at FRDA onset relates to exacerbation of the already dysregulated iron metabolism that plays a major role in the pathogenesis of FRDA.

The WT hemochromatosis protein HFE inhibits CD8⁺ T-lymphocyte activation

MHC class I (MHC I) antigen presentation is a ubiquitous process by which cells present endogenous proteins to CD8(+) T lymphocytes during immune surveillance and response. Hereditary hemochromatosis protein, HFE, is involved in cellular iron uptake but, while structurally homologous to MHC I, is unable to bind peptides. However, increasing evidence suggests a role for HFE in the immune system. Here, we investigated the impact of HFE on CD8(+) T-lymphocyte activation. Using transient HFE transfection assays in a model of APCs, we show that WT HFE (HFEWT ), but not C282Y-mutated HFE, inhibits secretion of MIP-1β from antigen-specific CD8(+) T lymphocytes. HFEWT expression also resulted in major decreases in CD8(+) T-lymphocyte activation as measured by 4-1BB expression. We further demonstrate that inhibition of CD8(+) T-lymphocyte activation was independent of MHC I surface levels, β2-m competition, HFE interaction with transferrin receptor, antigen origin, or epitope affinity. Finally, we identified the α1-2 domains of HFEWT as being responsible for inhibiting CD8(+) T-lymphocyte activation. Our data imply a new role for HFEWT in altering CD8(+) T-lymphocyte reactivity, which could modulate antigen immunogenicity.

Brain iron accumulation in aging and neurodegenerative disorders

Over the decades, various studies have established an association between accumulation of iron and both aging and neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. Excess levels of iron can lead to increased oxidative stress through Fenton chemistry, and depletion of iron can similarly have deleterious effects. In addition, metal ions are known to be involved in both Alzheimer's disease and Parkinson's disease protein aggregation. Metal ion chelators have been extensively investigated in preclinical models, and may prove to be appropriate for modulating brain iron levels in age-related neurodegenerative disorders. Investigating age-related iron deposition is vital, and can possibly aid in determining at-risk groups and diagnosing neurodegenerative diseases at an early stage. Novel imaging methods have enabled researchers to examine iron deposition in vivo, and offer a noninvasive method of monitoring the progression of accumulation, and possible therapeutic effects of chelating compounds.

The conundrum of iron in multiple sclerosis--time for an individualised approach

Although the involvement of immune mechanisms in multiple sclerosis (MS) is undisputed, some argue that there is insufficient evidence to support the hypothesis that MS is an autoimmune disease, and that the difference between immune- and autoimmune disease mechanisms has yet to be clearly delineated. Uncertainties surrounding MS disease pathogenesis and the modest efficacy of currently used disease modifying treatments (DMTs) in the prevention of disability, warrant the need to explore other possibilities. It is evident from the literature that people diagnosed with MS differ widely in symptoms and clinical outcome--some patients have a benign disease course over many years without requiring any DMTs. Attempting to include all patients into a single entity is an oversimplification and may obscure important observations with therapeutic consequences. In this review we advocate an individualised approach named Pathology Supported Genetic Testing (PSGT), in which genetic tests are combined with biochemical measurements in order to identify subgroups of patients requiring different treatments. Iron dysregulation in MS is used as an example of how this approach may benefit patients. The theory that iron deposition in the brain contributes to MS pathogenesis has caused uncertainty among patients as to whether they should avoid iron. However, the fact that a subgroup of people diagnosed with MS show clinical improvement when they are on iron supplementation emphasises the importance of individualised therapy, based on genetic and biochemical determinations.

Polymorphisms in the genes coding for iron binding and transporting proteins are associated with disability, severity, and early progression in multiple sclerosis

BACKGROUND

Iron involvement/imbalance is strongly suspected in multiple sclerosis (MS) etiopathogenesis, but its role is quite debated. Iron deposits encircle the veins in brain MS lesions, increasing local metal concentrations in brain parenchyma as documented by magnetic resonance imaging and histochemical studies. Conversely, systemic iron overload is not always observed. We explored the role of common single nucleotide polymorphisms (SNPs) in the main iron homeostasis genes in MS patients.

METHODS

By the pyrosequencing technique, we investigated 414 MS cases [Relapsing-remitting (RR), n=273; Progressive, n=141, of which: Secondary (SP), n=103 and Primary (PP), n=38], and 414 matched healthy controls. Five SNPs in 4 genes were assessed: hemochromatosis (HFE: C282Y, H63D), ferroportin (FPN1: -8CG), hepcidin (HEPC: -582AG), and transferrin (TF: P570S).

RESULTS

The FPN1-8GG genotype was overrepresented in the whole MS population (OR=4.38; 95%CI, 1.89-10.1; P<0.0001) and a similar risk was found among patients with progressive forms. Conversely, the HEPC -582GG genotype was overrepresented only in progressive forms (OR=2.53; 95%CI, 1.34-4.78; P=0.006) so that SP and PP versus RR yielded significant outputs (P=0.009). For almost all SNPs, MS disability score (EDSS), severity score (MSSS), as well as progression index (PI) showed a significant increase when comparing homozygotes versus individuals carrying other genotypes: HEPC -582GG (EDSS, 4.24±2.87 vs 2.78±2.1; P=0.003; MSSS, 5.6±3.06 vs 3.79±2.6; P=0.001); FPN1-8GG (PI, 1.11±2.01 vs 0.6±1.31; P=0.01; MSSS, 5.08±2.98 vs 3.85±2.8; P=0.01); HFE 63DD (PI, 1.63±2.6 vs 0.6±0.86; P=0.009). Finally, HEPC -582G-carriers had a significantly higher chance to switch into the progressive form (HR=3.55; 1.83-6.84; log-rank P=0.00006).

CONCLUSIONS

Polymorphisms in the genes coding for iron binding and transporting proteins, in the presence of local iron overload, might be responsible for suboptimal iron handling. This might account for the significant variability peculiar to MS phenotypes, particularly affecting MS risk and progression paving the way for personalized pharmacogenetic applications in the clinical practice.

Iron and ER stress in neurodegenerative disease

Neurodegenerative disease is a condition in which subpopulations of neuronal cells of the brain and spinal cord are selectively lost. A common event in many neurodegenerative diseases is the increased level of endoplasmic reticulum (ER) stress caused by accumulation and deposits of inclusion bodies that contain abnormal aggregated proteins. However, the basis of how ER stress contributes to the selective neuronal vulnerability and degeneration remain elusive. Iron accumulation in the central nerve system is consistently present in many neurodegenerative diseases. In the past 5 years we have begun to show a relationship between polymorphisms in the HFE (high iron) gene and the risk of neurodegenerative disorders. Recent findings have suggested a connection between ER stress and iron metabolism and neurodegeneration. Here we review how the different levels of chronic ER stress contribute to the different fates of neurons, namely the adaptive response and neuronal death. And, we discuss the roles of iron and HFE genotype in selective neuronal vulnerability and degeneration through modifying the ER stress level.

Pathogenic implications of iron accumulation in multiple sclerosis

Iron, an essential element used for a multitude of biochemical reactions, abnormally accumulates in the CNS of patients with multiple sclerosis (MS). The mechanisms of abnormal iron deposition in MS are not fully understood, nor do we know whether these deposits have adverse consequences, that is, contribute to pathogenesis. With some exceptions, excess levels of iron are represented concomitantly in multiple deep gray matter structures often with bilateral representation, whereas in white matter, pathological iron deposits are usually located at sites of inflammation that are associated with veins. These distinct spatial patterns suggest disparate mechanisms of iron accumulation between these regions. Iron has been postulated to promote disease activity in MS by various means: (i) iron can amplify the activated state of microglia resulting in the increased production of proinflammatory mediators; (ii) excess intracellular iron deposits could promote mitochondria dysfunction; and (iii) improperly managed iron could catalyze the production of damaging reactive oxygen species (ROS). The pathological consequences of abnormal iron deposits may be dependent on the affected brain region and/or accumulation process. Here, we review putative mechanisms of enhanced iron uptake in MS and address the likely roles of iron in the pathogenesis of this disease.

HFE gene polymorphisms and severity in Portuguese patients with multiple sclerosis

BACKGROUND

High iron concentrations have been reported in oligodendrocytes, myelin and macrophages in multiple sclerosis (MS) lesions. It has been proposed that HFE gene polymorphisms could have a role in MS.

METHODS

The C282Y and H63D HFE variants frequencies were determined in 373 patients with MS and compared with a normal population.

RESULTS

No significant association was found between HFE polymorphisms and disease susceptibility. An analysis of the association of genotypes with disease severity was performed, and the C282Y allele was more frequent in the aggressive group.

CONCLUSIONS

Patients carrying the C282Y variant seem to have a worse prognosis.

HFE mutations and transferrin C1/C2 polymorphism among Croatian patients with schizophrenia and schizoaffective disorder

The aim of this study was to investigate the possible influence of hemochromatosis gene mutations (HFE-C282Y and H63D) and transferrin gene C2 variant (TF-C2) on susceptibility to schizophrenia and schizoaffective disorder and/or age at first hospital admission. Genotyping was performed in 176 Croatian patients and 171 non-psychiatric Croatian controls using PCR-RFLP analyses. Regarding the H63D mutation, allele and genotype frequencies reached boundary statistical significance. Other allele and genotype distributions were not significantly different between two groups. We also analyzed age at first hospital admission as a continuous variable using the non-parametric Mann-Whitney U-test and Kruskal-Wallis test, and multiple regression analysis. The results of these tests were negative. We concluded that investigated HFE mutations and TF-C2 variant are not high-risk genetic variants for schizophrenia/schizoaffective disorder in our population. Also our data do not support their impact on age at onset of the first psychotic symptoms.

Mutant HFE H63D protein is associated with prolonged endoplasmic reticulum stress and increased neuronal vulnerability

A specific polymorphism in the hemochromatosis (HFE) gene, H63D, is over-represented in neurodegenerative disorders such as amyotrophic lateral sclerosis and Alzheimer disease. Mutations of HFE are best known as being associated with cellular iron overload, but the mechanism by which HFE H63D might increase the risk of neuron degeneration is unclear. Here, using an inducible expression cell model developed from a human neuronal cell line SH-SY5Y, we reported that the presence of the HFE H63D protein activated the unfolded protein response (UPR). This response was followed by a persistent endoplasmic reticulum (ER) stress, as the signals of UPR sensors attenuated and followed by up-regulation of caspase-3 cleavage and activity. Our in vitro findings were recapitulated in a transgenic mouse model carrying Hfe H67D, the mouse equivalent of the human H63D mutation. In this model, UPR activation was detected in the lumbar spinal cord at 6 months then declined at 12 months in association with increased caspase-3 cleavage. Moreover, upon the prolonged ER stress, the number of cells expressing HFE H63D in early apoptosis was increased moderately. Cell proliferation was decreased without increased cell death. Additionally, despite increased iron level in cells carrying HFE H63D, it appeared that ER stress was not responsive to the change of cellular iron status. Overall, our studies indicate that the HFE H63D mutant protein is associated with prolonged ER stress and chronically increased neuronal vulnerability.

Mutations in the hemochromatosis gene and the clinical outcome of multiple sclerosis

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system unsurpassed for its variability in disease outcome. Given a possible role for dysregulation of iron metabolism in MS disease pathogenesis, we investigated whether or not mutations in the HFE gene influence the prognosis of the disease. A cohort of sporadic MS cases, taken from opposite extremes of the putative distribution of long-term outcome using the most stringent clinical criteria to date, was used to determine the role of HFE on MS disease severity. This approach increases the effective sample size by some 40-fold. Genotyping the two sets of MS patients (112 benign and 51 malignant) provided no evidence to suggest that mutations in HFE have any outcome modifying activity, although small effects cannot be ruled out. The frequency of HFE mutations was not different in MS compared to the general population.

Hypothetical molecular mechanisms by which local iron overload facilitates the development of venous leg ulcers and multiple sclerosis lesions

This paper presents a hypothetical model of role for iron in the development of venous leg ulcers and multiple sclerosis. Elevated concentrations of iron were found in the skin affected by venous hypertension and also in the areas of brain with multiple sclerosis lesions. Individuals with hemochromatosis gene (HFE) mutations: C282Y and H63D, which result in a less efficient transport of iron by macrophages, are characterized by an increased risk for venous leg ulcer and multiple sclerosis. Multiple sclerosis is a T cell-mediated disease, and T cells probably participate in the development of venous ulcers. This deleterious role of ferric ions could be related to the regulation of T cell proliferation and apoptosis. Under normal conditions excessive accumulation of T cells cannot take place, because nitric oxide and interferon-gamma drive these cells toward apoptosis. However, in tissues with a high concentration of iron, T lymphocytes proliferate instead of undergoing apoptosis. This is possible due to the internalization of the INF-gammaR2 chain of the interferon-gamma receptor, the downregulation of inducible nitric oxide synthase expression in macrophages and the inactivation of the active site of caspases. Yet, it should be emphasized that this hypothesis does not claim for the increased concentration of iron as a direct causal factor for the development of venous ulcerations or multiple sclerosis, but rather, iron is a factor that modulates and exaggerates the autoimmune process. Iron chelators, administered systemically or locally, should potentially exhibit therapeutic and prophylactic activity against venous leg ulcers and multiple sclerosis.

Hereditary hemochromatosis genotypes and risk of ischemic stroke

OBJECTIVE

We tested the hypothesis that the HFE genotypes H63D/H63D, H63D/wild type, C282Y/H63D, C282Y/C282Y, and C282Y/wild type are risk factors for symptomatic carotid atherosclerosis, ischemic cerebrovascular disease (ICVD), and ischemic stroke.

METHODS

We performed an age- and gender-matched case-control study of 701 cases with symptomatic carotid atherosclerosis vs 2,777 controls, and a prospective study of 9,178 individuals from the Danish general population followed for 24 years, during which 504 developed ICVD, of whom 393 had ischemic stroke.

RESULTS

Genotype was not consistently associated with symptomatic carotid atherosclerosis. The cumulative incidences of ICVD and ischemic stroke by age were increased for H63D/H63D vs wild type/wild type (log-rank: p = 0.003 and p < 0.001). H63D/H63D vs wild type/wild type had an age- and multifactorially adjusted hazard ratio of 2.0 (95% CI: 1.2 to 3.2; p = 0.007) and 2.1 (1.3 to 3.5; p = 0.004) for ICVD and of 2.4 (1.4 to 4.0; p = 0.001) and 2.8 (1.7 to 4.6; p < 0.001) for ischemic stroke; these remained significant after correction for multiple comparisons. Other hereditary hemochromatosis genotypes were not associated with ICVD or ischemic stroke.

CONCLUSIONS

Hereditary hemochromatosis H63D homozygosity predicts a two- to threefold risk of ICVD and ischemic stroke.

Lack of clinical manifestation of hereditary haemochromatosis in South African patients with multiple sclerosis

Caucasian South African patients with multiple sclerosis (MS) were screened for the most common hereditary haemochromatosis (HH) mutations, H63D and C282Y, in order to determine the impact of iron overload on clinical outcome of MS. DNA screening for mutations H63D and C282Y in 118 apparently unrelated MS patients did not reveal significant differences in allele frequencies in comparison with a control group from the same population. Of 17 MS patients heterozygous for C282Y, 3 had below normal and none had above normal transferrin saturation levels. One of the index MS patients, and subsequently also her sister who also has MS, tested positive for two copies of mutation C282Y. Determination of iron status revealed high serum ferritin and transferrin saturation levels in both patients. However, the index patient, being unaware of her C282Y status, had received treatment for iron deficiency in the past and her MS symptoms were less severe than those of her sister who has been wheelchair bound for the past 12 years and who did not take iron supplements. Lack of clinical manifestation of HH without any signs of organ damage in the C282Y homozygous MS patients is in accordance with a role of iron dysregulation in the aetiology of MS.