Associations of genetically determined iron status across the phenome: A mendelian randomization study.

BACKGROUND: Iron is integral to many physiological processes, and variations in its levels, even within the normal range, can have implications for health. The objective of this study was to explore the broad clinical effects of varying iron status. METHODS AND FINDINGS: Genome-wide association study (GWAS) summary data obtained from 48,972 European individuals (55% female) across 19 cohorts in the Genetics of Iron Status Consortium were used to identify 3 genetic variants (rs1800562 and rs1799945 in the hemochromatosis gene [HFE] and rs855791 in the transmembrane protease serine 6 gene [TMPRSS6]) that associate with increased serum iron, ferritin, and transferrin saturation and decreased transferrin levels, thus serving as instruments for systemic iron status. Phenome-wide association study (PheWAS) of these instruments was performed on 424,439 European individuals (54% female) in the UK Biobank who were aged 40-69 years when recruited from 2006 to 2010, with their genetic data linked to Hospital Episode Statistics (HES) from April, 1995 to March, 2016. Two-sample summary data mendelian randomization (MR) analysis was performed to investigate the effect of varying iron status on outcomes across the human phenome. MR-PheWAS analysis for the 3 iron status genetic instruments was performed separately and then pooled by meta-analysis. Correction was made for testing of multiple correlated phenotypes using a 5% false discovery rate (FDR) threshold. Heterogeneity between MR estimates for different instruments was used to indicate possible bias due to effects of the genetic variants through pathways unrelated to iron status. There were 904 distinct phenotypes included in the MR-PheWAS analyses. After correcting for multiple testing, the 3 genetic instruments for systemic iron status demonstrated consistent evidence of a causal effect of higher iron status on decreasing risk of traits related to anemia (iron deficiency anemia: odds ratio [OR] scaled to a standard deviation [SD] increase in genetically determined serum iron levels 0.72, 95% confidence interval [CI] 0.64-0.81, P = 4 × 10-8) and hypercholesterolemia (hypercholesterolemia: OR 0.88, 95% CI 0.83-0.93, P = 2 × 10-5) and increasing risk of traits related to infection of the skin and related structures (cellulitis and abscess of the leg: OR 1.25, 95% CI 1.10-1.42, P = 6 × 10-4). The main limitations of this study relate to possible bias from pleiotropic effects of the considered genetic variants and misclassification of diagnoses in the HES data. Furthermore, this work only investigated participants with European ancestry, and the findings may not be applicable to other ethnic groups. CONCLUSIONS: Our findings offer novel, to our knowledge, insight into previously unreported effects of iron status, highlighting a potential protective effect of higher iron status on hypercholesterolemia and a detrimental role on risk of skin and skin structure infections. Given the modifiable and variable nature of iron status, these findings warrant further investigation.

The Effect of Iron Status on Risk of Coronary Artery Disease: A Mendelian Randomization Study-Brief Report.

OBJECTIVE: Iron status is a modifiable trait that has been implicated in cardiovascular disease. This study uses the Mendelian randomization technique to investigate whether there is any causal effect of iron status on risk of coronary artery disease (CAD). APPROACH AND RESULTS: A 2-sample Mendelian randomization approach is used to estimate the effect of iron status on CAD risk. Three loci (rs1800562 and rs1799945 in the HFE gene and rs855791 in TMPRSS6) that are each associated with serum iron, transferrin saturation, ferritin, and transferrin in a pattern suggestive of an association with systemic iron status are used as instruments. SNP (single-nucleotide polymorphism)-iron status association estimates are based on a genome-wide association study meta-analysis of 48 972 individuals. SNP-CAD estimates are derived by combining the results of a genome-wide association study meta-analysis of 60 801 CAD cases and 123 504 controls with those of a meta-analysis of 63 746 CAD cases and 130 681 controls obtained from Metabochip and genome-wide association studies. Combined Mendelian randomization estimates are obtained for each marker by pooling results across the 3 instruments. We find evidence of a protective effect of higher iron status on CAD risk (iron odds ratio, 0.94 per SD unit increase; 95% confidence interval, 0.88-1.00; P=0.039; transferrin saturation odds ratio, 0.95 per SD unit increase; 95% confidence interval, 0.91-0.99; P=0.027; log-transformed ferritin odds ratio, 0.85 per SD unit increase; 95% confidence interval, 0.73-0.98; P=0.024; and transferrin odds ratio, 1.08 per SD unit increase; 95% confidence interval, 1.01-1.16; P=0.034). CONCLUSIONS: This Mendelian randomization study supports the hypothesis that higher iron status reduces CAD risk. These findings may highlight a therapeutic target.

Raised serum ferritin concentration in hereditary hyperferritinemia cataract syndrome is not a marker for iron overload.

Hyperferritinemia and bilateral cataracts are features of the rare hereditary hyperferritinemia cataract syndrome (HHCS; OMIM #600886). HHCS is an autosomal dominant condition caused by mutations which increase expression of the ferritin light polypeptide (FTL) gene. We report a patient with HHCS who was misdiagnosed and treated as having hemochromatosis, in whom a heterozygous c.-160A>G mutation was identified in the iron responsive element (IRE) of FTL, causing ferritin synthesis in the absence of iron overload. This report demonstrates the need for clinical awareness of HHCS as a cause of hyperferritinemia in the absence of iron overload and provides a possible diagnostic schema.

Wilson's disease.

Progressive hepatolenticular degeneration, or Wilson's disease, is a genetic disorder of copper metabolism. Knowledge of the clinical presentations and treatment of the disease are important both to the generalist and to specialists in gastroenterology and hepatology, neurology, psychiatry, and paediatrics. Wilson's disease invariably results in severe disability and death if untreated. The diagnosis is easily overlooked but if discovered early, effective treatments are available that will prevent or reverse many manifestations of this disorder. Studies have identified the role of copper in disease pathogenesis and clinical, biochemical, and genetic markers that can be useful in diagnosis. There are several chelating agents and zinc salts for medical therapy. Liver transplantation corrects the underlying pathophysiology and can be lifesaving. The discovery of the Wilson's disease gene has opened up a new molecular diagnostic approach, and could form the basis of future gene therapy.

Hepatic iron concentration, fibrosis and response to venesection associated with the A77D and V162del "loss of function" mutations in ferroportin disease.

Ferroportin disease is an autosomal dominant form of hemochromatosis associated with siderosis in cells of the mononuclear phagocyte system and, to varying degrees, in hepatocytes. Ferroportin was investigated as a candidate gene in two pedigrees with hyperferritinaemia and siderosis in mononuclear phagocytes. The entire ferroportin coding region was sequenced and hepatic iron concentration, histology and response to treatment were determined. The results were compared with previously reported cases. The A77D mutation was detected in patient 1, his father (patient 2) and his brother (patient 3), who had portal fibrosis. The V162del mutation was detected in patient 4, who developed anemia after the third weekly venesection. While the disease is rare, A77D and V162del are the most common ferroportin mutations in Caucasians. The spectrum of clinical expression of these two mutations was reviewed in all cases described to date. These mutations were associated with fibrosis in about a third of cases. For A77D and V162del, this analysis confirms that the threshold hepatic iron concentration for development of fibrosis may be higher than for classical hemochromatosis. These two mutations, which both decreased iron export in cell culture studies, give rise to similar patterns of clinical expression and morbidity, although the highest hepatic iron concentrations have been observed with A77D. It is important for clinicians to consider ferroportin disease in cases where there are features of iron overload unrelated to HFE, autosomal dominant inheritance and/or iron deposition in mononuclear phagocytes.

Screening for hemochromatosis and iron overload: satisfaction with results notification and understanding of mailed results in unaffected participants of the HEIRS study.

AIM: The purpose of this study was to assess the level of satisfaction and understanding of test results, by a sample of non-C282Y homozygous participants in the hemochromatosis and iron overload screening (HEIRS) study, who received serum ferritin (SF), transferrin saturation (TS), and HFE gene test results by mail. METHODS: Approximately 1 month after receiving test results by mail, participants were surveyed about understanding of and satisfaction with results notification. RESULTS: Overall, participants were satisfied with receiving test results by mail. Participants receiving results with one or two HFE mutations or TS and/or SF levels outside the normal range (an "alert value") were less likely to be satisfied with this method of notification. Participants with normal HFE test results understood their results and recommendations better than those with one or two mutations. Although all participants received results letters in their native language, English-speaking participants had higher mean understanding scores than Mandarin, Vietnamese, or Spanish-speaking participants. CONCLUSION: Participants were satisfied with receiving test results by mail. However, the level of understanding of the results was not sufficient for this mode of results notification to stand alone, especially for non-English speaking participants, and all participants with one or more test results outside the normal range.

Results communication and patient education after screening for possible hemochromatosis and iron overload: experience from the HEIRS Study of a large ethnically and linguistically diverse group.

PURPOSE: We assessed the effectiveness of educational interventions for conveying clinical findings and information about hereditary hemochromatosis (HH) and iron overload (IO) to individuals evaluated clinically after initial screening for HH/IO with serum ferritin (SF) concentration, transferrin saturation (TS), and HFE genotyping. METHODS: A questionnaire mailed to 2300 cases and controls 1 month after a letter summarizing clinical findings measured understanding of results and recommendations, knowledge of HH/IO, and satisfaction with information received. RESULTS: Of 1622 (70.5%) participants completing relevant items, 83.6% were satisfied with receiving initial screening results by mail, 93.4% found information clear and easy to understand, 89.2% generally felt they got enough information, but 47.5% still had questions. C282Y/C282Y homozygosity with normal TS/SF predicted the best understanding of genetic results. Many with no mutations thought relatives were at risk. Iron levels created most confusion, and a third incorrectly recalled treatment recommendations. Having any abnormal result, lower education, older age, and being non-white, and/or non-English speaking predicted lower understanding. CONCLUSIONS: Combining genotypic and phenotypic screening for HH/IO creates additional difficulties in communicating results-particularly to those with low health literacy. Explaining aberrant iron TS and SF levels and low-risk genotypes, follow-up recommendations, and risk to relatives will need creative, culturally appropriate strategies.

HFE gene in primary and secondary hepatic iron overload.

Distinct from hereditary haemochromatosis, hepatic iron overload is a common finding in several chronic liver diseases. Many studies have investigated the prevalence, distribution and possible contributory role of excess hepatic iron in non-haemochromatotic chronic liver diseases. Indeed, some authors have proposed iron removal in liver diseases other than hereditary haemochromatosis. However, the pathogenesis of secondary iron overload remains unclear. The High Fe (HFE) gene has been implicated, but the reported data are controversial. In this article, we summarise current concepts regarding the cellular role of the HFE protein in iron homeostasis. We review the current status of the literature regarding the prevalence, hepatic distribution and possible therapeutic implications of iron overload in chronic hepatitis C, hepatitis B, alcoholic and non-alcoholic fatty liver diseases and porphyria cutanea tarda. We discuss the evidence regarding the role of HFE gene mutations in these liver diseases. Finally, we summarize the common and specific features of iron overload in liver diseases other than haemochromatosis.

Psychosocial impact of genetic testing for hemochromatosis in the HEIRS Study: a comparison of participants recruited in Canada and in the United States.

The Hemochromatosis and Iron Overload Screening (HEIRS) Study screened 101,168 participants recruited from primary-care clinics in Canada and the United States. The present study investigated differences in the psychological effects of genetic screening for hemochromatosis (HFE mutation analysis) in participants from each country. Study participants comprised a subset of 2,654 individuals who donated blood for HFE mutation analysis. The initial screening and 1-month post-result questionnaires included measures of General Health, Mental Health (SF-36), and a measure of the percentage of individuals who experienced at least one example of worry in response to the genetic testing. Participants reported similar changes in general health and mental health, regardless of mutation result, or country. Although a significantly lower percentage of Canadian participants than U.S. participants indicated at least one negative emotional response to the genetic testing, greater than 50% of C282Y homozygote participants (the gene mutation most strongly associated with hemochromatosis) from both countries experienced such in response to testing. Thus, although not serious enough to affect individuals' mental or physical health, there was evidence of at least one element of negative emotional response to the genetic testing. These findings suggest that population screening for common HFE mutations associated with hemochromatosis risk has similar psychological effects on Canadian and U.S. individuals, although fewer Canadians may experience a negative response to such testing.

Fatty liver in H63D homozygotes with hyperferritinemia.

To study the clinical correlates of the H63D mutation we have analysed the phenotype of H63D homo-zygotes identified through mutation analysis in a referral laboratory. A total of 366 blood samples referred for HFE analysis were screened for C282Y and H63D mutations. Four H63D homozygotes were identified. All had raised serum ferritin but normal transferrin saturation. They were negative for hepatitis B and C and only one patient consumed excess alcohol. In all 4 cases ultrasonography revealed fatty liver. In two patients a liver biopsy was done and showed mild siderosis with an unusual distribution and macrovesicular steatosis. These data confirm the association between fatty liver, hyperferritinaemia and increased hepatic iron, but do not clarify whether siderosis was related to steatosis rather than homozygosity for the H63D mutation. Patients with fatty liver may complicate the interpretation of data in population studies of the expression of H63D homozygosity.

Predictors of belief that genetic test information about hemochromatosis should be shared with family members.

We queried 101,951 white, Hispanic, black, Asian, American Indian (i.e., American Indian or Alaska Native in the United States and North American Indian, Metis, or Inuit in Canada) and Pacific Islander (including Native Hawaiian) adults who agreed to be genotypically and phenotypically screened for hemochromatosis as part of the Hemochromatosis and Iron Overload Screening (HEIRS) study about their views on sharing genetic test information with family members. Multiple logistic regression (adjusting for study site, age group, race/ethnicity, preferred language, gender, education group, income group, SF-36 General Health and Mental Health subscales, perceived benefits and limitations of genetic testing, and belief that genetic testing is a good idea) evaluated independent predictors of responding "Strongly Agree" or "Agree" versus "Disagree" or "Strongly Disagree" to the statement "Information about a person's genetic risk should be shared with family members". Agreement that genetic risk information should be shared with family members was high (93% in the overall sample of 78,952 who answered this question), but differed among racial/ethnic groups. Hispanics were significantly less likely to agree that genetic test information should be shared with family members (i.e., 88% versus 92% or more among all other ethnicities). The relationship of perceived limitations and benefits of testing, gender, and age group to the belief that information should be shared differed among racial/ethnic groups, with Spanish-preferring Hispanics being the most different from other subgroups.

Replication and Characterization of Association between ABO SNPs and Red Blood Cell Traits by Meta-Analysis in Europeans.

Red blood cell (RBC) traits are routinely measured in clinical practice as important markers of health. Deviations from the physiological ranges are usually a sign of disease, although variation between healthy individuals also occurs, at least partly due to genetic factors. Recent large scale genetic studies identified loci associated with one or more of these traits; further characterization of known loci and identification of new loci is necessary to better understand their role in health and disease and to identify potential molecular mechanisms. We performed meta-analysis of Metabochip association results for six RBC traits-hemoglobin concentration (Hb), hematocrit (Hct), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular volume (MCV) and red blood cell count (RCC)-in 11 093 Europeans from seven studies of the UCL-LSHTM-Edinburgh-Bristol (UCLEB) Consortium. We identified 394 non-overlapping SNPs in five loci at genome-wide significance: 6p22.1-6p21.33 (with HFE among others), 6q23.2 (with HBS1L among others), 6q23.3 (contains no genes), 9q34.3 (only ABO gene) and 22q13.1 (with TMPRSS6 among others), replicating previous findings of association with RBC traits at these loci and extending them by imputation to 1000 Genomes. We further characterized associations between ABO SNPs and three traits: hemoglobin, hematocrit and red blood cell count, replicating them in an independent cohort. Conditional analyses indicated the independent association of each of these traits with ABO SNPs and a role for blood group O in mediating the association. The 15 most significant RBC-associated ABO SNPs were also associated with five cardiometabolic traits, with discordance in the direction of effect between groups of traits, suggesting that ABO may act through more than one mechanism to influence cardiometabolic risk.

Portal vein thrombosis: what is the role of genetics?

The aetiology of portal vein thrombosis (PVT) in adults is complex. Risk factors include local precipitating factors and acquired and inherited factors, an area in which there has been much recent progress. Although PVT in the absence of cirrhosis may be regarded as a somewhat different disorder to PVT in the presence of cirrhosis, in both cases most studies support a role of the prothrombin G20210A mutation. Some differences in risk factors observed between different studies may relate partly to referral patterns or study design, although individual patients may develop PVT as a result of differing combinations of risk factors. The demonstration of an inherited thrombophilic mutation in a subset of PVT may ultimately inform clinical management regarding the use and duration of anticoagulation therapy, although there is a need for evidence from randomized-controlled clinical trial data.

Demonstration of the presence of the "deleted" MIR122 gene in HepG2 cells.

MicroRNA 122 (miR-122) is highly expressed in the liver where it influences diverse biological processes and pathways, including hepatitis C virus replication and metabolism of iron and cholesterol. It is processed from a long non-coding primary transcript (~7.5 kb) and the gene has two evolutionarily-conserved regions containing the pri-mir-122 promoter and pre-mir-122 hairpin region. Several groups reported that the widely-used hepatocytic cell line HepG2 had deficient expression of miR-122, previously ascribed to deletion of the pre-mir-122 stem-loop region. We aimed to characterise this deletion by direct sequencing of 6078 bp containing the pri-mir-122 promoter and pre-mir-122 stem-loop region in HepG2 and Huh-7, a control hepatocytic cell line reported to express miR-122, supported by sequence analysis of cloned genomic DNA. In contrast to previous findings, the entire sequence was present in both cell lines. Ten SNPs were heterozygous in HepG2 indicating that DNA was present in two copies. Three validation isolates of HepG2 were sequenced, showing identical genotype to the original in two, whereas the third was different. Investigation of promoter chromatin status by FAIRE showed that Huh-7 cells had 6.2 ± 0.19- and 2.7 ± 0.01- fold more accessible chromatin at the proximal (HNF4α-binding) and distal DR1 transcription factor sites, compared to HepG2 cells (p=0.03 and 0.001, respectively). This was substantiated by ENCODE genome annotations, which showed a DNAse I hypersensitive site in the pri-mir-122 promoter in Huh-7 that was absent in HepG2 cells. While the origin of the reported deletion is unclear, cell lines should be obtained from a reputable source and used at low passage number to avoid discrepant results. Deficiency of miR-122 expression in HepG2 cells may be related to a relative deficiency of accessible promoter chromatin in HepG2 versus Huh-7 cells.

Genetic counseling gone awry: miscommunication between prenatal genetic service providers and Mexican-origin clients.

Amniocentesis, and other prenatal genetic tests, have become a well-established feature of modern prenatal care. But these tests place a considerable decision-making burden on the expectant mothers to whom they are offered: the genetic issues involved are complex and the appropriate course of action sometimes ambiguous. Genetic counseling aims to help pregnant clients make an informed decision about prenatal genetic tests. But the clientele of prenatal genetic counseling has changed significantly in the years since the practice was established. Clients were once a self-selected group of women well-informed about the genetic services being offered. In contrast, clients now include an increasing number of women, particularly ethnic minority women, who had no prior knowledge of genetic testing, but were found to be at risk of birth defects after routine screening. Little is known about how well genetic counseling serves the needs of this new clientele. This paper investigates the possibility that miscommunication between genetic counselors and their Mexican-origin clients contributed to the higher rates of amniocentesis refusal. We interviewed 156 pregnant Mexican-origin women who screened positive on a blood test routinely offered in California to detect birth defects. We also observed the genetics consultations of a sub-sample of the women. We identified five common sources of miscommunication: (1) Medical jargon; (2) The non-directive nature of counseling; (3) The inhibitions of counselors stemming from misplaced cultural sensitivity; (4) Problems of translation; (5) Problems of trust. We found that many Mexican-origin women are skeptical of genetic testing and do not easily surrender their own lay theories about the causes of their condition. In order to dislodge the misunderstandings of their clients, counselors must give clients the opportunity to air their own views, however contrary to those of genetics professionals these may be.

Hemochromatosis and Iron Overload Screening (HEIRS) study design for an evaluation of 100,000 primary care-based adults.

BACKGROUND: The HEIRS Study will evaluate the prevalence, genetic and environmental determinants, and potential clinical, personal, and societal impact of hemochromatosis and iron overload in a multiethnic, primary care-based sample of 100,000 adults over a 5-year period. Participants are recruited from 5 Field Centers. Laboratory testing and data management and analysis are performed in a Central Laboratory and Coordinating Center, respectively. METHODS: Participants undergo testing for serum iron measures and common mutations of the hemochromatosis gene ( ) on chromosome 6p and answer questions on demographics, health, and genetic testing attitudes. Participants with elevated values of transferrin saturation and serum ferritin and/or C282Y homozygosity are invited to undergo a comprehensive clinical examination (CCE), as are frequency-matched control subjects. These examinations provide data on personal and family medical history, lifestyle characteristics, physical examination, genetic counseling, and assessment of ethical, legal, and social implications. Primary and secondary causes of iron overload will be distinguished by clinical criteria. Iron overload will be confirmed by quantification of iron stores. Recruiting family members of cases will permit DNA analysis for additional genetic factors that affect iron overload. RESULTS: Of the first 50,520 screened, 51% are white, 24% are African American, 11% are Asian, 11% are Hispanic, and 3% are of other, mixed, or unidentified race; 63% are female and 37% are male. CONCLUSIONS: Information from the HEIRS Study will inform policy regarding the feasibility, optimal approach, and potential individual and public health benefits and risks of primary care-based screening for iron overload and hemochromatosis.

Defective tumor necrosis factor release from Crohn's disease macrophages in response to Toll-like receptor activation: relationship to phenotype and genome-wide association susceptibility loci.

BACKGROUND: Recent work provides evidence of a failure of acute inflammation in Crohn's disease (CD), and suggests that the primary defect operates at the level of the macrophage and cytokine release. Here we extend the characterization of the innate immune defect in CD by investigating the macrophage response to Toll-like receptor (TLR) agonists and assess potential links between genome-wide association study (GWAS) susceptibility loci, disease phenotype, and therapeutic regimens on tumor necrosis factor α (TNF) release. METHODS: Peripheral blood-derived macrophages were cultured from control subjects and patients with CD, stimulated with TLR ligands, and the release of TNF measured. Genomic DNA was purified from blood and genotyped for 34 single nucleotide polymorphisms (SNPs) identified as being associated with CD by GWAS. RESULTS: All stimuli resulted in a reduction (32%-48%) in TNF release from macrophages derived from CD patients (n = 28-101) compared to those from healthy control (HC) subjects. All phenotypes demonstrated impaired TNF release, with the greatest defect in patients with colonic disease. There was no detectable relationship between the level of TNF released and the presence of GWAS susceptibility loci in CD patients. Reduced TNF levels were not influenced by age, gender, or use of aminosalicylate (5-ASA) medication. CONCLUSIONS: This study supports the hypothesis of defective proinflammatory cytokine secretion and an innate immunodeficiency in CD. Abnormal TNF secretion is evident downstream of multiple TLRs, affects all disease phenotypes, and is unrelated to 34 polymorphisms associated with CD by GWAS.