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Baas FS, Rishi G, Swinkels DW, Subramaniam VN. Genetic Diagnosis in Hereditary Hemochromatosis: Discovering and Understanding the Biological Relevance of Variants. Clin Chem 2021; 67:1324-1341. [PMID: 34402502 DOI: 10.1093/clinchem/hvab130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 06/23/2021] [Indexed: 11/13/2022]
Abstract
BACKGROUND Hereditary hemochromatosis (HH) is a genetic disease, leading to iron accumulation and possible organ damage. Patients are usually homozygous for p. Cys282Tyr in the homeostatic iron regulator gene but may have mutations in other genes involved in the regulation of iron. Next-generation sequencing is increasingly being utilized for the diagnosis of patients, leading to the discovery of novel genetic variants. The clinical significance of these variants is often unknown. CONTENT Determining the pathogenicity of such variants of unknown significance is important for diagnostics and genetic counseling. Predictions can be made using in silico computational tools and population data, but additional evidence is required for a conclusive pathogenicity classification. Genetic disease models, such as in vitro models using cellular overexpression, induced pluripotent stem cells or organoids, and in vivo models using mice or zebrafish all have their own challenges and opportunities when used to model HH and other iron disorders. Recent developments in gene-editing technologies are transforming the field of genetic disease modeling. SUMMARY In summary, this review addresses methods and developments regarding the discovery and classification of genetic variants, from in silico tools to in vitro and in vivo models, and presents them in the context of HH. It also explores recent gene-editing developments and how they can be applied to the discussed models of genetic disease.
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Affiliation(s)
- Floor S Baas
- Translational Metabolic Laboratory (TML 831), Radboudumc, Nijmegen, the Netherlands.,Hepatogenomics Research Group, School of Biomedical Sciences, Queensland University of Technology (QUT), Brisbane, QLD, Australia
| | - Gautam Rishi
- Hepatogenomics Research Group, School of Biomedical Sciences, Queensland University of Technology (QUT), Brisbane, QLD, Australia
| | - Dorine W Swinkels
- Translational Metabolic Laboratory (TML 831), Radboudumc, Nijmegen, the Netherlands
| | - V Nathan Subramaniam
- Hepatogenomics Research Group, School of Biomedical Sciences, Queensland University of Technology (QUT), Brisbane, QLD, Australia
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Dysregulated hepcidin response to dietary iron in male mice with reduced Gnpat expression. Biosci Rep 2020; 40:226001. [PMID: 32766721 PMCID: PMC7441371 DOI: 10.1042/bsr20201508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2020] [Revised: 07/13/2020] [Accepted: 08/06/2020] [Indexed: 11/17/2022] Open
Abstract
Exome sequencing has identified the glyceronephosphate O-acyltransferase (GNPAT) gene as a genetic modifier of iron overload in hereditary hemochromatosis (HH). Subjects with HFE (Homeostatic Iron Regulator) p.C282Y mutations and the GNPAT p.D519G variant had more iron loading compared with subjects without the GNPAT variant. In response to an oral iron challenge, women with GNPAT polymorphisms loaded more iron as compared with women without polymorphisms, reinforcing a role for GNPAT in iron homeostasis. The aim of the present study was to develop and characterize an animal model of disease to further our understanding of genetic modifiers, and in particular the role of GNPAT in iron homeostasis. We generated an Hfe/Gnpat mouse model reminiscent of the patients previously studied and studied these mice for up to 26 weeks. We also examined the effect of dietary iron loading on mice with reduced Gnpat expression. Gnpat heterozygosity in Hfe knockout mice does not play a role in systemic iron homeostasis; Gnpat+/− mice fed a high-iron diet, however, had lower hepatic hepcidin (HAMP) mRNA expression, whereas they have significantly higher serum iron levels and transferrin saturation compared with wildtype (WT) littermates on a similar diet. These results reinforce an independent role of GNPAT in systemic iron homeostasis, reproducing in an animal model, the observations in women with GNPAT polymorphisms subjected to an iron tolerance test.
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Secondes ES, Wallace DF, Rishi G, McLaren GD, McLaren CE, Chen WP, Ramm LE, Powell LW, Ramm GA, Barton JC, Subramaniam VN. Increased frequency of GNPAT p.D519G in compound HFE p.C282Y/p.H63D heterozygotes with elevated serum ferritin levels. Blood Cells Mol Dis 2020; 85:102463. [PMID: 32652459 DOI: 10.1016/j.bcmd.2020.102463] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 06/30/2020] [Accepted: 06/30/2020] [Indexed: 12/12/2022]
Abstract
Glyceronephosphate O-acyltransferase (GNPAT) p.D519G (rs11558492) was identified as a genetic modifier correlated with more severe iron overload in hemochromatosis through whole-exome sequencing of HFE p.C282Y homozygotes with extreme iron phenotypes. We studied the prevalence of p.D519G in HFE p.C282Y/p.H63D compound heterozygotes, a genotype associated with iron overload in some patients. Cases were Australian participants with elevated serum ferritin (SF) levels ≥300μg/L (males) and ≥200μg/L (females); subjects whose SF levels were below these cut-offs were designated as controls. Samples were genotyped for GNPAT p.D519G. We compared the allele frequency of the present subjects, with/without elevated SF, to p.D519G frequency in public datasets. GNPAT p.D519G was more prevalent in our cohort of p.C282Y/p.H63D compound heterozygotes with elevated SF (37%) than European public datasets: 1000G 21%, gnomAD 20% and ESP 21%. We conclude that GNPAT p.D519G is associated with elevated SF in Australian HFE p.C282Y/p.H63D compound heterozygotes.
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Affiliation(s)
- Eriza S Secondes
- School of Biomedical Sciences, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.
| | - Daniel F Wallace
- School of Biomedical Sciences, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.
| | - Gautam Rishi
- School of Biomedical Sciences, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.
| | - Gordon D McLaren
- Division of Hematology/Oncology, Department of Medicine, University of California, Irvine, CA, USA; Department of Veterans Affairs Long Beach Healthcare System, Long Beach, CA, USA.
| | | | - Wen-Pin Chen
- Chao Family Comprehensive Cancer Center, University of California, Irvine, CA.
| | - Louise E Ramm
- QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
| | - Lawrie W Powell
- QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
| | - Grant A Ramm
- QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
| | - James C Barton
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, USA, Southern Iron Disorders Center, Birmingham, AL, USA
| | - V Nathan Subramaniam
- School of Biomedical Sciences, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia; QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
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An P, Wang J, Wang H, Jiang L, Wang J, Min J, Wang F. Gnpat does not play an essential role in systemic iron homeostasis in murine model. J Cell Mol Med 2020; 24:4118-4126. [PMID: 32108988 PMCID: PMC7171407 DOI: 10.1111/jcmm.15068] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 01/14/2020] [Accepted: 01/16/2020] [Indexed: 12/13/2022] Open
Abstract
The GNPAT variant rs11558492 (p.D519G) was identified as a novel genetic factor that modifies the iron‐overload phenotype in homozygous carriers of the HFE p.C282Y variant. However, the reported effects of the GNPAT p.D519G variant vary among study populations. Here, we investigated the role of GNPAT in iron metabolism using Gnpat‐knockout (Gnpat−/−), Gnpat/Hfe double‐knockout (Gnpat−/−Hfe−/− or DKO) mice and hepatocyte‐specific Gnpat‐knockout mice (Gnpatfl/fl;Alb‐Cre). Our analysis revealed no significant difference between wild‐type (Gnpat+/+) and Gnpat−/− mice, between Hfe−/− and DKO mice, or between Gnpatfl/fl and Gnpatfl/fl;Alb‐Cre with respect to serum iron and tissue iron. In addition, the expression of hepcidin was not affected by deleting Gnpat expression in the presence or absence of Hfe. Feeding Gnpat−/− and DKO mice a high‐iron diet had no effect on tissue iron levels compared with wild‐type and Hfe−/− mice, respectively. Gnpat knockdown in primary hepatocytes from wild‐type or Hfe−/− mice did not alter hepcidin expression, but it repressed BMP6‐induced hepcidin expression. Taken together, these results support the hypothesis that deleting Gnpat expression has no effect on either systemic iron metabolism or the iron‐overload phenotype that develops in Hfe−/− mice, suggesting that GNPAT does not directly mediate iron homeostasis under normal or high‐iron dietary conditions.
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Affiliation(s)
- Peng An
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, China Agricultural University, Beijing, China
| | - Jiaming Wang
- School of Public Health, The First Affiliated Hospital, Institute of Translational Medicine, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, School of Medicine, Zhejiang University, Hangzhou, China
| | - Hao Wang
- Precision Nutrition Innovation Center, School of Public Health, Zhengzhou University, Zhengzhou, China
| | - Li Jiang
- School of Public Health, The First Affiliated Hospital, Institute of Translational Medicine, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, School of Medicine, Zhejiang University, Hangzhou, China
| | - Jia Wang
- Precision Nutrition Innovation Center, School of Public Health, Zhengzhou University, Zhengzhou, China
| | - Junxia Min
- School of Public Health, The First Affiliated Hospital, Institute of Translational Medicine, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, School of Medicine, Zhejiang University, Hangzhou, China
| | - Fudi Wang
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, China Agricultural University, Beijing, China.,School of Public Health, The First Affiliated Hospital, Institute of Translational Medicine, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, School of Medicine, Zhejiang University, Hangzhou, China.,Precision Nutrition Innovation Center, School of Public Health, Zhengzhou University, Zhengzhou, China
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