Transmembrane Protease Serine 6 Research Articles

The association of TMPRSS6 gene polymorphism with iron status in Egyptian children (a pilot study)

Several studies have shown association of single nucleotide polymorphisms (SNPs) of hepcidin regulatory pathways genes with impaired iron status. The most common is in the TMPRSS6 gene. In Africa, very few studies have been reported. We aimed to investigate the correlation between the common SNPs in the transmembrane protease, serine 6 (TMPRSS6) gene and iron indicators in a sample of Egyptian children for identifying the suitable candidate for iron supplementation.Patients and methods One hundred and sixty children aged 5–13 years were included & classified into iron deficient, iron deficient anemia and normal healthy controls. All were subjected to assessment of serum iron, serum ferritin, total iron binding capacity, complete blood count, reticulocyte count, serum soluble transferrin receptor and serum hepcidin. Molecular study of TMPRSS6 genotyping polymorphisms (rs4820268, rs855791 and rs11704654) were also evaluated.Results There was an association of iron deficiency with AG of rs855791 SNP, (P = 0.01). The minor allele frequency for included children were 0.43, 0.45 & 0.17 for rs4820268, rs855791 & rs11704654 respectively. Genotype GG of rs4820268 expressed the highest hepcidin gene expression fold, the lowest serum ferroportin & iron store compared to AA and AG genotypes (p = 0.05, p = 0.05, p = 0.03 respectively). GG of rs855791 had lower serum ferritin than AA (p = 0.04), lowest iron store & highest serum hepcidin compared to AA and AG genotypes (p = 0.04, p = 0.01 respectively). Children having CC of rs11704654 had lower level of hemoglobin, serum ferritin and serum hepcidin compared with CT genotype (p = 0.01, p = 0.01, p = 0.02) respectively.Conclusion Possible contribution of SNPs (rs855791, rs4820268 and rs11704654) to low iron status.

Pharmacophore-based computational study on inhibitor of TMPRSS6 as hepcidin modulator in an iron overload of beta-thalassaemia

ABSTRACT TMPRSS6 (transmembrane protease, serine 6) plays an important role in the cleavage of hemojuvelin (HJV), a key protein involved in the regulation of hepcidin metabolism. TMPRSS6 cleaves HJV at specific sites, leading to the activation of the bone morphogenetic protein (BMP6-SMAD) pathway. This pathway further leads to the production of hepcidin (a liver peptide enzyme), which promotes iron absorption and removal from the bloodstream. In-silico pharmacophore analysis is used in this study to identify potential small therapeutic compounds that inhibit TMPRSS6 activity. Pharmacophore investigations of known inhibitors (peptidomimetic benzothiazole) were carried out to identify the molecules’ important properties for interacting with the target. The pharmacophore model of the TMPRSS6 (PDB ID: 6N4T) inhibitor (KD7) pharmacophore features were used to screen the small molecules library that binds to the target and modulates its activity. The docking parameters of the top 5 hit molecules had lower binding energy in comparative analysis to reference molecule. The best-fit pharmacophore feature ligands were docked at the binding site of the target protein. This study demonstrates that knocking out the enzyme reduces the effects of iron overload in conditions like hemochromatosis and beta-thalassemia. In-silico investigation discovered significant evidence of catalytic activity.

TMPRSS6 gene mutations in six Saudi families with iron refractory iron deficiency anemia

Iron-refractory iron deficiency anemia (IRIDA) is considered an autosomal recessive iron deficiency anemia due to mutations in the transmembrane protease serine 6 (TMPRSS6) gene. Variations in iron parameters and a higher risk of iron deficiency have been linked to the TMPRSS6 mutations. Furthermore, human genome-wide association studies (GWAS) identified a common mutation (rs855791) linked to abnormal hematological parameters, highlighting the importance of the TMPRSS6 gene in the regulation of iron homeostasis. This is the first study to investigate TMPRSS6 gene mutation in six Saudi families of probands with iron deficiency anemia unresponsive to oral iron and partially responsive to parenteral iron administration. Each participant provided a vacutainer tube with three blood samples (2.5 ml each) and analyzed based on hematological, biochemical iron profiles, and followed by genotyping by PCR. The TMPRSS6 gene was amplified, sequenced, and analyzed in all probands and family members. Statistical analysis was done using SPSS and SHEsis software. Few functional mutations in these families were suggested (p.W73X, p.E523K and p.V736A). The proband of family 6 presented numerous hematological abnormalities upon initial consultation, including normocytic anemia accompanied by low Hb, normal MCV, low serum iron, low serum ferritin, and normal TIBC. While the p.W73X variant was only found in 2 families, the p.V736A variant was found in all examined Saudi families with IRIDA. Given the evidence outlined for these six cases, future genotype-phenotype correlation studies in a large number of IRIDA patients in Saudi Arabia may be very informative for patient management, in addition to increasing knowledge of TMPRSS6 function during development as well as factors in the regulation of TMPRSS6 and its effect on iron levels in the body.

Treating Iron Overload Disorders with a Novel Therapeutic Antibody Targeting TMPRSS6

Iron is an essential element for almost all living organisms as it participates in a wide variety of metabolic processes. Disorders of iron metabolism are among the most prevalent human diseases, ranging from anemia to hemochromatosis. Excessive iron accumulations in major organs of iron overload patients can lead to high mortality. Hepcidin, a HAMP-encoded liver hormone, is the master regulator of iron homeostasis. By binding to the sole iron exporter ferroportin and causing internalization and degradation of the complex, hepcidin inhibits cellular iron efflux, thereby lowers plasma iron levels. Inappropriately suppressed/low hepcidin production is central to iron overload. Transmembrane protease serine-6 (TMPRSS6), a type II transmembrane serine protease primarily expressed in liver, downregulates hepcidin expression through BMP-SMAD pathway. TMPRSS6 deficiencies have been shown to cause hepcidin overexpression in both TMPRSS6-mutant mice and in patients with iron-refractory iron deficiency anemia (IRIDA). Therefore, TMPRSS6 is a viable therapeutic target for iron overload disorders.Here we report the generation of an anti-TMPRSS6 antibody through a hybridoma campaign using a DNA-based immunization approach, followed by humanization and sequence optimization. Lead antibody, hzMWTx-003 selectively binds human TMPRSS6 with low nanomolar affinity (KD: 7.6nM), and is cross-reactive to rodent (mouse and rat) and monkey (cynomolgus and rhesus) TMPRSS6. Single-dose injection of hzMWTx-003 was able to significantly elevate serum hepcidin and liver HAMP RNA levels in wildtype mice, resulting in significantly reduced serum iron level. The Hbb th3/+ mouse model of β-thalassemia, like its human counterpart, is characterized by iron overload, ineffective erythropoiesis and splenomegaly. Treatment of Hbb th3/+mice with MWTx-003 effectively increased hepcidin expression at both protein and RNA levels, leading to significantly reduced serum iron and liver non-heme iron content. MWTx-003 also dramatically improved anemia and ineffective erythropoiesis, and alleviated splenomegaly in these mice.CMC development of hzMWTx-003 confirms outstanding biophysical properties. Preliminary studies in cynomolgus monkey using GLP-grade material demonstrated good pharmacokinetics of hzMWTx-003 and expected pharmacodynamic response where reduction of serum iron could be sustained for 21 days after single dose administration. A single dose toxicology study in cynomolgus monkey revealed no safety concerns, and no production of anti-idiotype antibodies was detected. In summary, anti-TMPRSS6 antibody MWTx-003 represents a promising therapy for iron overload disorders such as β-thalassemia, and potentially other diseases where iron restriction is beneficial. DisclosuresChen: Mabwell Therapeutics Inc: Current Employment. Wang: Mabwell Therapeutics Inc: Current Employment. Zheng: Mabwell (Shanghai) Bioscience Co. Ltd: Current Employment. Huang: Mabwell Therapeutics Inc: Current Employment. Mao: Mabwell (Shanghai) Bioscience Co. Ltd.: Current Employment. Ouyang: Mabwell (Shanghai) Bioscience Co. Ltd.: Current Employment. Du: Mabwell Therapeutics Inc: Current Employment.

Association of common\xa0TMPRSS6 and TF gene variants with hepcidin and iron status in healthy rural Gambians

Genome-wide association studies in Europeans and Asians have identified numerous variants in the transmembrane protease serine 6 (TMPRSS6) and transferrin (TF) genes that are associated with changes in iron status. We sought to investigate the effects of common TMPRSS6 and TF gene SNPs on iron status indicators in a cohort of healthy Africans from rural Gambia. We measured iron biomarkers and haematology traits on individuals participating in the Keneba Biobank with genotype data on TMPRSS6 (rs2235321, rs855791, rs4820268, rs2235324, rs2413450 and rs5756506) and TF (rs3811647 and rs1799852), n = 1316. After controlling for inflammation, age and sex, we analysed the effects of carrying either single or multiple iron-lowering alleles on iron status. TMPRSS6 rs2235321 significantly affected plasma hepcidin concentrations (AA genotypes having lower hepcidin levels; F ratio 3.7, P = 0.014) with greater impact in individuals with low haemoglobin or ferritin. No other TMPRSS6 variant affected hepcidin. None of the TMPRSS6 variants nor a TMPRSS6 allele risk score affected other iron biomarkers or haematological traits. TF rs3811647 AA carriers had 21% higher transferrin (F ratio 16.0, P < 0.0001), 24% higher unsaturated iron-binding capacity (F ratio 12.8, P < 0.0001) and 25% lower transferrin saturation (F ratio 4.3, P < 0.0001) compared to GG carriers. TF rs3811647 was strongly associated with transferrin, unsaturated iron-binding capacity (UIBC) and transferrin saturation (TSAT) with a single allele effect of 8–12%. There was no association between either TF SNP and any haematological traits or iron biomarkers. We identified meaningful associations between TMPRSS6 rs2235321 and hepcidin and replicated the previous findings on the effects of TF rs3811647 on transferrin and iron binding capacity. However, the effects are subtle and contribute little to population variance. Further genetic and functional studies, including polymorphisms frequent in Africa populations, are needed to identify markers for genetically stratified approaches to prevention or treatment of iron deficiency anaemia.

Genetic analysis of TMPRSS6 gene in Saudi female patients with iron deficiency anemia

Objective/backgroundMutations in transmembrane protease serine 6 (TMPRSS6) gene induce high hepcidin level, which causes iron-refractory iron deficiency anemia (IRIDA) by preventing duodenal iron absorption. This study aims to identify the common genetic variations of the TMPRSS6 gene that affect iron levels among Saudi female patients with iron deficiency anemia (IDA). MethodsAll study participants were Saudi females (12–49 years old): 32 patients with IDA, 32 patients with IRIDA, and 34 healthy individuals comprising the control group. Hematological investigations, iron profile, serum hepcidin level, and TMPRSS6 gene transcription were determined. The TMPRSS6 gene was amplified, sequenced, and analyzed among all study participants. ResultsThe mean hepcidin and TMPRSS6 RNA transcription levels in IDA and IRIDA groups were significantly lower than those in the control group. TMPRSS6 gene sequence analysis detected 41 variants: two in the 5′ untranslated region (5′UTR), 17 in introns, and 22 in exons. Thirty-three variants were previously reported in the Single Nucleotide Polymorphism Database, and eight variants were novel; one novel variant was in 5′UTR (g.-2 T > G); five novel variants were detected in exons (p.W73X, p.D479N, p.E523K, p.L674L, and p.I799I). At the time of the sequence analysis of our samples, two variants—p.D479N and p.674L—were novel. However, these variants are present at a very low allele frequency in other populations (L674L, 0.00007761 and D479N, 0.000003980). ConclusionThis is the first study to investigate the genetic variants of TMPRSS6 gene in Saudi female patients with IDA. The generated data will serve as a reference for future studies on IDA in the Arab population.

Associations of TMPRSS6 Polymorphisms with Gestational Diabetes Mellitus in Chinese Han Pregnant Women: a Preliminary Cohort Study.

Body iron status is likely to be associated with type 2 diabetes (T2DM) and gestational diabetes mellitus (GDM); transmembrane protease serine 6 (TMPRSS6) polymorphisms may be associated with T2DM risk through their effects on body iron status. However, it remains unknown whether the TMPRSS6 single nucleotide polymorphisms (SNPs) affect the risk of GDM development. We aimed to determine whether the TMPRSS6 SNPs rs855791 (V736A) and rs4820268 (D521D) are associated with the risk of GDM in pregnant women. The two SNPs in TMPRSS6 gene were genotyped and examined for their associations with body iron status and GDM risk in 398 unrelated Chinese Han pregnant women. The 2 TMPRSS6 SNPs rs855791 and rs4820268 were both significantly associated with serum iron and transferrin saturation (P < 0.01 for all) rather than ferritin. After adjustment for covariates, the C allele of rs4820268 was nominally and significantly associated with an increased risk of GDM (OR = 2.531; 95%CI = 1.044-6.136, P = 0.040); when concentrations of ferritin were further adjusted, the association was still significant (OR = 2.528; 95%CI = 1.043-6.126, P = 0.040). There was a significant trend (P = 0.065) in the association between the T allele of rs855791 and an increased GDM risk in this study population. The 2 TMPRSS6 SNPs rs855791 and rs4820268 were both significantly associated with serum iron and transferrin saturation, and TMPRSS6 variants might be associated with the risk of GDM. Furthermore, the effects of TMPRSS6 SNPs on the risk of GDM may not be completely explained by the mediation of body iron status. Further studies are warranted.

A Review on Iron-Refractory Iron-Deficiency Anemia

Anemia is a common and predominant blood disorder globally, in which the level of hemoglobin or healthy red blood cells are abnormally lower. The most common type of anemia is iron-deficiency anemia (IDA), and the treatment is iron supplementation to the individuals. In some conditions, the iron supplementation does not alter the hemoglobin range, which means the iron given is not taken up by the body of the individual. This condition is found to be iron-refractory IDA (IRIDA). It is the genetic condition, in which the hepcidin, an iron regulatory hormone expression is altered. IRIDA is a rare genetic disorder, which is autosomal recessive in inheritance pattern. Hepcidin alteration blocks the iron absorption, which in turn causes anemic condition. The transmembrane protease serine 6 (TMPRSS6) gene is involved in negative regulation of hepcidin along with the encoding of matriptase-2 enzyme, which is crucial for iron balance in the human body. Matriptase-2 regulates the iron homeostasis by balancing the hepcidin hormone. The genetic polymorphisms in the TMPRSS6 gene result in this a rare type of anemic condition. Therefore, this review particularly focuses on the IRIDA and TMPRSS6 gene, hepcidin, and matriptase-2 enzyme. The review on IRIDA is being found to be important since the clear metabolism of hepcidin and matriptase-2 in iron metabolism are still unclear.

TMPRSS6 Gene Polymorphism and Serum Hepcidin in Iron Deficiency Anemia

Background: Iron deficiency anemia (IDA) is a global health problem and common medical condition seen in everyday clinical practice. Hepcidin which is the key regulator of iron homeostasis, that down-regulates iron export by binding to ferroportin which is expressed on the surface of iron-releasing cells, leading to its degradation thus reducing plasma iron levels. Overexpression of hepcidin leads to iron deficiency anemia. Matriptase-2 (MT-2) which is encoded by transmembrane protease serine 6 (TMPRSS6) gene regulates hepcidin expression. Objective: Was to evaluate the role of TMPRSS6 gene polymorphisms and serum hepcidin level in IDA patients. Subjects and methods: This study was carried out on 30 patients with iron deficiency anemia and 30 age and sex matched individuals as control group. Patients were subdivided into (group 1) 14 patients with acquired iron deficiency anemia (IDA) and (group 2)16 patients with iron refractory iron deficiency anemia(IRIDA).TMPRSS6 gene single nucleotide polymorphisms(SNPS), (rs4820268)and(rs855791)were evaluated using real time – polymerase chain reaction (RT-PCR) while serum hepcidin level was measured by enzyme linked immunosorbent assay (ELISA). Results: There was a significant increase in frequency of the TMPRSS6 SNPs rs855791 and rs 4820268 separately in IRIDA group compared to IDA group,(P=0.003),(P=0.007) respectivelyand to control group(P=0.000) and (P=0.000) respectively.Also, there was highly significant increase in frequency of both mutations together in IRIDA group compared to IDA group (P=0.000) and to control group (P=0.000). In IDA group there was a significant increase in the frequency of TMPRSS6 SNPs rs 855791 when compared to control group (P=0.013), and a non-significant difference in frequency of SNPs rs 4820268 when compared to control group (P=0.092).Also, there was a non-significant difference in frequency of both mutations together in IDA group in comparison to control group (P> 0.05).There was a highly significant decrease in serum hepcidin level in IDA group and highly significant increase in hepcidin levels in IRIDA group compared to control group (P=0.000).In IRIDA patients group only there was highly significant increase in hepcidin level in those with mutation in both SNPs together (rs4820268 and rs855791) than patients with one mutation or with wild type(P=0.000).There was a significant decrease in Hb and iron and highly significant decrease in MCV, MCH and ferritin in IRIDA patients with mutation of both SNPs together (rs 4820268 and rs855791) compared to one mutation or wild type (P=0.015,0.016,0.002 ,0.000, 0.006 respectively).Also, there was highly significant decrease in Hb, MCV, MCH and ferritin in IDA patients with mutation of both SNPs together(rs 4820268 and rs 855791) compared to one mutation or wild type (P= 0.002,0.002 ,0.004, 0.009 respectively). In IDA patients there was a significant positive correlation between hepcidin and ferritin (P =0.034, r = 0.279),while there was a significant negative correlation between hepcidin and MCH in IRIDA group (P =0.032, r = - 0.536).Conclusion: In IRIDA the rs4820268 and rs855791 mutations separately or in combination lack inhibitory effect on hepcidin and consequently iron profile and hemoglobin while in IDA although there was significant increase in frequency of rs855791 mutations, there was no effect on hepcidin which suggests that the rs 4820268 mutation is necessary for affecting hepcidin either alone or in combination with rs 855791 mutation. In IDA, there may be other mechanisms or mutations causing anemia.

The Association of TMPRSS6 Gene Polymorphism and Iron Intake with Iron Status among Under-Two-Year-Old Children in Lombok, Indonesia.

Multiple common variants in transmembrane protease serine 6 (TMPRSS6) were associated with the plasma iron concentration in genome-wide association studies, but their effect in young children where anemia and iron deficiency (ID) were prevalent has not been reported, particularly taking account of iron intake. This study aims to investigate whether TMPRSS6 SNPs (rs855791 and rs4820268) and iron intake are associated with a low iron and hemoglobin concentration in under-two-year-old children. The study analyzed the baseline of a randomized trial (NUPICO, ClinicalTrials.gov NCT01504633) in East Lombok, Indonesia. Children aged 6–17 months (n = 121) were included in this study. The multiple linear regressions showed that TMPRSS6 decreased serum ferritin (SF) by 4.50 g/L per copy minor allele (A) of rs855791 (p = 0.08) and by 5.00 μg/L per copy minor allele (G) of rs4820268 (p = 0.044). There were no associations between rs855791 and rs4820268 with soluble transferrin receptor (sTfR) and hemoglobin (Hb) concentration (rs855791; p = 0.38 and p = 0.13, rs4820268; p = 0.17 and p = 0.33). The finding suggests the need for further studies to explore whether the nutrient recommendation for iron should be based on genetic characteristics, particularly for children who have mutation in TMPRSS6.

Identification of an iron-responsive subtype in two children diagnosed with relapsing-remitting multiple sclerosis using whole exome sequencing

BackgroundMultiple sclerosis is a disorder related to demyelination of axons. Iron is an essential cofactor in myelin synthesis. Previously, we described two children (males of mixed ancestry) with relapsing-remitting multiple sclerosis (RRMS) where long-term remission was achieved by regular iron supplementation. A genetic defect in iron metabolism was postulated, suggesting that more advanced genetic studies could shed new light on disease pathophysiology related to iron. MethodsWhole exome sequencing (WES) was performed to identify causal pathways. Blood tests were performed over a 10 year period to monitor the long-term effect of a supplementation regimen. Clinical wellbeing was assessed quarterly by a pediatric neurologist and regular feedback was obtained from the schoolteachers. ResultsWES revealed gene variants involved in iron absorption and transport, in the transmembrane protease, serine 6 (TMPRSS6) and transferrin (TF) genes; multiple genetic variants in CUBN, which encodes cubilin (a receptor involved in the absorption of vitamin B12 as well as the reabsorption of transferrin-bound iron and vitamin D in the kidneys); SLC25A37 (involved in iron transport into mitochondria) and CD163 (a scavenger receptor involved in hemorrhage resolution). Variants were also found in COQ3, involved with synthesis of Coenzyme Q10 in mitochondria. Neither of the children had the HLA-DRB1*1501 allele associated with increased genetic risk for MS, suggesting that the genetic contribution of iron-related genetic variants may be instrumental in childhood MS. In both children the RRMS has remained stable without activity over the last 10 years since initiation of nutritional supplementation and maintenance of normal iron levels, confirming the role of iron deficiency in disease pathogenesis in these patients. ConclusionOur findings highlight the potential value of WES to identify heritable risk factors that could affect the reabsorption of transferrin-bound iron in the kidneys causing sustained iron loss, together with inhibition of vitamin B12 absorption and vitamin D reabsorption (CUBN) and iron transport into mitochondria (SLC25A37) as the sole site of heme synthesis. This supports a model for RRMS in children with an apparent iron-deficient biochemical subtype of MS, with oligodendrocyte cell death and impaired myelination possibly caused by deficits of energy- and antioxidant capacity in mitochondria.

Transmembrane Protease, Serine 6 (TMPRSS6) Antisense Oligonucleotide (IONIS-TMPRSS6-LRX) Reduces Plasma Iron Levels of Healthy Volunteers in a Phase 1 Clinical Study

Iron overload is the major cause of morbidity and mortality in beta-thalassemia patients. The low levels of beta-globin and ineffective erythropoiesis in these patients result in the suppression of hepcidin. The inappropriately low levels of hepcidin trigger an increased absorption of dietary iron and increased iron release from storage, causing iron overload. Expression of hepcidin, which is predominately produced in the liver, is negatively regulated by the transmembrane protease, serine 6 (TMPRSS6). Mouse and human genetic data indicated that lowering TMPRSS6 expression could up-regulate hepcidin and ameliorate many of the disease symptoms associated with beta-thalassemia. Previously we identified a highly specific and potent antisense oligonucleotide (ASO) targeting either the murine (Guo et al. J Clin Invest. 2013; 123(4):1531-41) or the human (Aghajan et al, Blood 2016; 128:1013) TMPRSS6 mRNA. Downregulation of TMPRSS6 with ASO treatment resulted in dose-dependent hepcidin upregulation, leading to dramatic reductions in serum iron and transferrin saturation in animal models This in turn ameliorated the anemia and iron overload phenotypes in a mouse model of beta-thalassemia (th3/+ mice), which recapitulates beta-thalassemia intermedia in humans.Herein, we are reporting the initial clinical safety and pharmacodynamics of IONIS-TMPRSS6-LRX. This GalNAc-conjugated, TMPRSS6 ASO was evaluated in a placebo-controlled, double-blind, randomized, single-center Phase 1 clinical study enrolling healthy volunteers. During an 8-week period, placebo or IONIS-TMPRSS6-LRX was administered subcutaneously four times (Weeks 1, 4, 6 and 8) at doses of 20, 40 or 60 mg. At doses of 20 and 40 mg, mean (±SEM) levels of serum iron were reduced 34±10% and 49±7% on week 10 (The 60 mg treatment cohort is ongoing). Consistent with the reduction of plasma iron, the mean (+/-SEM) percent transferrin saturation was reduced from baseline levels of 28±3% and 30±1% to 14±2% and 13±2%, for 20 and 40 mg groups, respectively, at Week 10. Furthermore, plasma hepcidin levels were increased from 2.1±0.6 and 2.5±0.6 nM to 2.7±0.6 and 6.7±0.9 nM, respectively. During this time period, there were small reductions in Hgb (-9±2%), reticulocyte Hgb (-13±2%) at the 40 mg dose. There were no serious adverse events in the study and the treatment-emergent adverse events were generally mild. In summary, IONIS-TMPRSS6-LRX, a novel antisense oligonucleotide targeting TMPRSS6, effectively reduces plasma iron levels and has the potential as a therapeutic for patients with beta-thalassemia and related disorders. The safety profile of IONIS-TMPRSS6-LRX supports further development. DisclosuresMcCaleb:Ionis Pharmaceuticals, INC: Employment, Equity Ownership. Lickliter:Nucleus Network: Employment. Dibble:Ionis Pharmaceuticals, INC: Employment. Schneider:Ionis Pharmaceuticals, INC: Employment, Other: shareholders. Aghajan:Ionis Pharmaceuticals, Inc: Employment. Guo:Ionis Pharmaceuticals, Inc: Employment. Hughes:Ionis Pharmaceuticals, INC: Employment, Other: shareholders. Geary:Ionis Pharmaceuticals, INC: Employment, Other: shareholders. Monia:Ionis Pharmaceuticals, Inc: Employment, Other: Intellectual property rights.

Genome-wide association study of iron traits and relation to diabetes in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL): potential genomic intersection of iron and glucose regulation?

Genetic variants contribute to normal variation of iron-related traits and may also cause clinical syndromes of iron deficiency or excess. Iron overload and deficiency can adversely affect human health. For example, elevated iron storage is associated with increased diabetes risk, although mechanisms are still being investigated. We conducted the first genome-wide association study of serum iron, total iron binding capacity (TIBC), transferrin saturation, and ferritin in a Hispanic/Latino cohort, the Hispanic Community Health Study/Study of Latinos (>12 000 participants) and also assessed the generalization of previously known loci to this population. We then evaluated whether iron-associated variants were associated with diabetes and glycemic traits. We found evidence for a novel association between TIBC and a variant near the gene for protein phosphatase 1, regulatory subunit 3B (PPP1R3B; rs4841132, β = -0.116, P = 7.44 × 10-8). The effect strengthened when iron deficient individuals were excluded (β = -0.121, P = 4.78 × 10-9). Ten of sixteen variants previously associated with iron traits generalized to HCHS/SOL, including variants at the transferrin (TF), hemochromatosis (HFE), fatty acid desaturase 2 (FADS2)/myelin regulatory factor (MYRF), transmembrane protease, serine 6 (TMPRSS6), transferrin receptor (TFR2), N-acetyltransferase 2 (arylamine N-acetyltransferase) (NAT2), ABO blood group (ABO), and GRB2 associated binding protein 3 (GAB3) loci. In examining iron variant associations with glucose homeostasis, an iron-raising variant of TMPRSS6 was associated with lower HbA1c levels (P = 8.66 × 10-10). This association was attenuated upon adjustment for iron measures. In contrast, the iron-raising allele of PPP1R3B was associated with higher levels of fasting glucose (P = 7.70 × 10-7) and fasting insulin (P = 4.79 × 10-6), but these associations were not attenuated upon adjustment for TIBC-so iron is not likely a mediator. These results provide new genetic information on iron traits and their connection with glucose homeostasis.

Common Variants and Haplotypes in the TF, TNF-α, and TMPRSS6 Genes Are Associated with Iron Status in a Female Black South African Population1–3

Background: It is unknown whether single nucleotide polymorphisms (SNPs), associated with iron status in European and Asian populations, have the same relation within the African population.Objectives: We investigated associations of reported SNPs with iron markers in a South African cohort.Methods: Hemoglobin concentration, serum ferritin (SF) and soluble transferrin receptor (sTfR) concentrations, and body iron (BI) stores were measured in women (n = 686; range, 32–86 y) who were part of the Prospective Urban and Rural Epidemiology study. Thirty-two SNPs in 12 genes were selected based on existing genome-wide association study data.Results: In the transferrin (TF) gene, SF and BI were significantly lower in the heterozygote genotype (AG) of reference SNP (rs) 1799852 (P = 0.01 and 0.03, respectively) and sTfR concentrations were significantly higher (P = 0.004) than the homozygote minor allele genotype (AA), whereas transferrin receptor and BI concentrations were significantly lower in the heterozygote genotype (AG) of rs3811647 (both P = 0.03) than the homozygote wild-type (AA) and minor allele groups (GG). The chromosome 6 allele combination (AAA) consisting of rs1799964 and rs1800629 both in tumor necrosis factor-α (TNF-α) and rs2071592 in nuclear factor κB inhibitor–like protein 1 (NFKBIL1) was associated with higher odds for low SF concentrations (SF < 15 μg/L; OR: 1.86; 95% CI: 1.23, 2.79) than the allele combinations AGA, GGT, and AGT. The chromosome 22 allele combination (GG) consisting of rs228918 and rs228921 in the transmembrane protease serine 6 (TMPRSS6) gene was associated with lower odds for increased sTfR concentrations (sTfR > 8.3mg/L; OR: 0.79; 95% CI: 0.63, 0.98) than the allele combination AA.Conclusions: Various SNPs and allele combinations in the TF, TNF-α, and TMPRSS6 genes are associated with iron status in black South African women; however, these association patterns are different compared with European ancestry populations. This stresses the need for population-specific genomic data.

Erratum to: Inter-ethnic differences in genetic variants within the transmembrane protease, serine 6 (TMPRSS6) gene associated with iron status indicators: a systematic review with meta-analyses.

Transmembrane protease, serine 6 (TMPRSS6), is likely to be involved in iron metabolism through its pleiotropic effect on hepcidin concentrations. Recently, genome-wide association studies have identified common variants in the TMPRSS6 gene to be linked to anaemia and low iron status. To get a more precise evaluation of identified TMPRSS6 single nucleotide polymorphism associations with iron status in cohorts of differing continental ancestry, we conducted a systematic review with meta-analyses. We searched the literature using HuGE Navigator, Pubmed and Scopus databases for primarily genome-wide association studies using TMPRSS6 as a free term. Fixed-effects meta-analysis was used to obtain summary estimates of associations. Eleven studies comprised Caucasian populations, four included an Asian population and one study included an African-American population. Differences in minor allele frequencies of 8 TMPRSS6 SNPs (rs855791, rs4820268, rs2111833, rs1421312, rs228921, rs228918, rs228919 and rs575620) across ethnic groups were observed, with the MAF of rs855791 significantly higher in Asian populations than in Caucasians (0.55 vs 0.42, P < 0.0001). In the meta-analysis, the A allele of rs855791 was associated with lower Hb and ferritin concentrations in all populations. This allele was also associated with increased serum transferrin receptor and transferrin concentrations. We observed similar associations for the G allele in rs4820268. Clear disparities in associations were found for the African-American population, although not statistically significant. Associations between TMPRSS6 SNPs and anaemia are consistent across Caucasian and Asian populations. This study highlights the need to conduct studies in African populations where iron deficiency is of utmost public health significance.

Inter-ethnic differences in genetic variants within the transmembrane protease, serine 6 (TMPRSS6) gene associated with iron status indicators: a systematic review with meta-analyses.

Transmembrane protease, serine 6 (TMPRSS6), is likely to be involved in iron metabolism through its pleiotropic effect on hepcidin concentrations. Recently, genome-wide association studies have identified common variants in the TMPRSS6 gene to be linked to anaemia and low iron status. To get a more precise evaluation of identified TMPRSS6 single nucleotide polymorphism associations with iron status in cohorts of differing continental ancestry, we conducted a systematic review with meta-analyses. We searched the literature using HuGE Navigator, Pubmed and Scopus databases for primarily genome-wide association studies using TMPRSS6 as a free term. Fixed-effects meta-analysis was used to obtain summary estimates of associations. Eleven studies comprised Caucasian populations, four included an Asian population and one study included an African-American population. Differences in minor allele frequencies of 8 TMPRSS6 SNPs (rs855791, rs4820268, rs2111833, rs1421312, rs228921, rs228918, rs228919 and rs575620) across ethnic groups were observed, with the MAF of rs855791 significantly higher in Asian populations than in Caucasians (0.55 vs 0.42, P<0.0001). In the meta-analysis, the A allele of rs855791 was associated with lower Hb and ferritin concentrations in all populations. This allele was also associated with increased serum transferrin receptor and transferrin concentrations. We observed similar associations for the G allele in rs4820268. Clear disparities in associations were found for the African-American population, although not statistically significant. Associations between TMPRSS6 SNPs and anaemia are consistent across Caucasian and Asian populations. This study highlights the need to conduct studies in African populations where iron deficiency is of utmost public health significance.

Functional and clinical impact of novel TMPRSS6 variants in iron-refractory iron-deficiency anemia patients and genotype-phenotype studies.

Iron-refractory iron-deficiency anemia (IRIDA) is a rare autosomal-recessive disorder characterized by hypochromic microcytic anemia, low transferrin saturation, and inappropriate high levels of the iron hormone hepcidin. The disease is caused by variants in the transmembrane protease serine 6 (TMPRSS6) gene that encodes the type II serine protease matriptase-2, a negative regulator of hepcidin transcription. Sequencing analysis of the TMPRSS6 gene in 21 new IRIDA patients from 16 families with different ethnic origin reveal 17 novel mutations, including the most frequent mutation in Southern Italy (p.W590R). Eight missense mutations were analyzed in vitro. All but the p.T287N variant impair matriptase-2 autoproteotylic activation, decrease the ability to cleave membrane HJV and inhibit the HJV-dependent hepcidin activation. Genotype-phenotype studies in IRIDA patients have been so far limited due to the relatively low number of described patients. Our genotype-phenotype correlation analysis demonstrates that patients carrying two nonsense mutations present a more severe anemia and microcytosis and higher hepcidin levels than the other patients. We confirm that TMPRSS6 mutations are spread along the gene and that mechanistically they fully or partially abrogate hepcidin inhibition. Genotyping IRIDA patients help in predicting IRIDA severity and may be useful for predicting response to iron treatment.

Iron and hepcidin: a story of recycling and balance

To avoid iron deficiency and overload, iron availability is tightly regulated at both the cellular and systemic levels. The liver peptide hepcidin controls iron flux to plasma from enterocytes and macrophages through degradation of the cellular iron exporter ferroportin. The hepcidin-ferroportin axis is essential to maintaining iron homeostasis. Genetic inactivation of proteins of the hepcidin-activating pathway causes iron overload of varying severity in human and mice. Hepcidin insufficiency and increased iron absorption are also characteristic of anemia due to ineffective erythropoiesis in which, despite high total body iron, hepcidin is suppressed by the high erythropoietic activity, worsening both iron overload and anemia in a vicious cycle. Hepcidin excess resulting from genetic inactivation of a hepcidin inhibitor, the transmembrane protease serine 6 (TMPRSS6) leads to a form of iron deficiency refractory to oral iron. Increased hepcidin explains the iron sequestration and iron-restricted erythropoiesis of anemia associated with chronic inflammatory diseases. In mice, deletion of TMPRSS6 in vivo has profound effects on the iron phenotype of hemochromatosis and beta-thalassemia. Hepcidin manipulation to restrict iron is a successful strategy to improve erythropoiesis in thalassemia, as shown clearly in preclinical studies targeting TMPRSS6; attempts to control anemia of chronic diseases by antagonizing the hepcidin effect are ongoing. Finally, the metabolic pathways identified from iron disorders are now being explored in other human pathologic conditions, including cancer.

Genetic Variants Influencing Biomarkers of Nutrition Are Not Associated with Cognitive Capability in Middle-Aged and Older Adults

AbstractSeveral investigations have observed positive associations between good nutritional status, as indicated by micronutrients, and cognitive measures; however, these associations may not be causal. Genetic polymorphisms that affect nutritional biomarkers may be useful for providing evidence for associations between micronutrients and cognitive measures. As part of the Healthy Ageing across the Life Course (HALCyon) program, men and women aged between 44 and 90 y from 6 UK cohorts were genotyped for polymorphisms associated with circulating concentrations of iron [rs4820268 transmembrane protease, serine 6 (TMPRSS6) and rs1800562 hemochromatosis (HFE)], vitamin B-12 [(rs492602 fucosyltransferase 2 (FUT2)], vitamin D ([rs2282679 group-specific component (GC)] and β-carotene ([rs6564851 beta-carotene 15,15'-monooxygenase 1 (BCMO1)]. Meta-analysis was used to pool within-study effects of the associations between these polymorphisms and the following measures of cognitive capability: word recall, phonemic fluency, semantic fluency, and search speed. Among the several statistical tests conducted, we found little evidence for associations. We found the minor allele of rs1800562 was associated with poorer word recall scores [pooled β on Z-score for carriers vs. noncarriers: −0.05 (95% CI: −0.09, −0.004); P = 0.03, n = 14,105] and poorer word recall scores for the vitamin D–raising allele of rs2282679 [pooled β per T allele: −0.03 (95% CI: −0.05, −0.003); P = 0.03, n = 16,527]. However, there was no evidence for other associations. Our findings provide little evidence to support associations between these genotypes and cognitive capability in older adults. Further investigations are required to elucidate whether the previous positive associations from observational studies between circulating measures of these micronutrients and cognitive performance are due to confounding and reverse causality.

Administration of recombinant erythropoietin alone does not improve the phenotype in iron refractory iron deficiency anemia patients

Mutations in transmembrane protease, serine 6 (TMPRSS6) cause iron refractory iron deficiency anemia (IRIDA). Parenteral iron administration may slightly improve hemoglobin level but is troublesome for patients. Optimal treatment has yet to be determined. We identified five patients from four independent families displaying the IRIDA picture with truncating biallelic mutations in TMPRSS6, one of which is novel. Liver iron determined by superconducting quantum interference device biosusceptometry ranged from 390 to 720 µg Fe/g wet weight (normal range 100-500; n = 3). Intestinal iron absorption (12 and 32 %, normal range 10-50; n = 2) and 59Fe erythrocyte incorporation after ingestion of 59Fe (57 and 38 %, normal range 70-90; n = 2) were inadequately low for iron-deficient anemic individuals. Baseline serum erythropoietin was elevated or borderline high in four patients. Administration of recombinant human erythropoietin (rhEPO) at up to 273 and 188 U/kg body weight/week alone did not improve anemia or result in a decrease of urinary hepcidin in two individuals. In conclusion, the ability of exogenous rhEPO to increase hemoglobin level appears to be impaired in IRIDA.