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Uguen K, Le Tertre M, Tchernitchko D, Elbahnsi A, Maestri S, Gourlaouen I, Férec C, Ka C, Callebaut I, Le Gac G. The dual loss and gain of function of the FPN1 iron exporter results in the ferroportin disease phenotype. HGG ADVANCES 2024; 5:100335. [PMID: 39039793 PMCID: PMC11343060 DOI: 10.1016/j.xhgg.2024.100335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2024] [Revised: 07/16/2024] [Accepted: 07/16/2024] [Indexed: 07/24/2024] Open
Abstract
Heterozygous mutations in SLC40A1, encoding a multi-pass membrane protein of the major facilitator superfamily known as ferroportin 1 (FPN1), are responsible for two distinct hereditary iron-overload diseases: ferroportin disease, which is associated with reduced FPN1 activity (i.e., decrease in cellular iron export), and SLC40A1-related hemochromatosis, which is associated with abnormally high FPN1 activity (i.e., resistance to hepcidin). Here, we report three SLC40A1 missense variants with opposite functional consequences. In cultured cells, the p.Arg40Gln and p.Ser47Phe substitutions partially reduced the ability of FPN1 to export iron and also partially reduced its sensitivity to hepcidin. The p.Ala350Val substitution had more profound effects, resulting in low FPN1 iron egress and weak FPN1/hepcidin interaction. Structural analyses helped to differentiate the first two substitutions, which are predicted to cause local instabilities, and the third, which is thought to prevent critical rigid-body movements that are essential to the iron transport cycle. The phenotypic traits observed in a total of 12 affected individuals are highly suggestive of ferroportin disease. Our findings dismantle the classical dualism of FPN1 loss versus gain of function, highlight some specific and unexpected functions of FPN1 transmembrane helices in the molecular mechanism of iron export and its regulation by hepcidin, and extend the spectrum of rare genetic variants that may cause ferroportin disease.
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Affiliation(s)
- Kevin Uguen
- University Brest, Inserm, EFS, UMR 1078, GGB, 29200 Brest, France; CHU de Brest, 29200 Brest, France
| | - Marlène Le Tertre
- University Brest, Inserm, EFS, UMR 1078, GGB, 29200 Brest, France; CHU de Brest, 29200 Brest, France
| | - Dimitri Tchernitchko
- CHU Paris Nord-Val de Seine - Hôpital Xavier Bichat-Claude Bernard, 75018 Paris, France; Centre de Recherche sur l'Inflammation, Inserm U1149, 75018 Paris, France
| | - Ahmad Elbahnsi
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005 Paris, France
| | - Sandrine Maestri
- University Brest, Inserm, EFS, UMR 1078, GGB, 29200 Brest, France
| | | | - Claude Férec
- University Brest, Inserm, EFS, UMR 1078, GGB, 29200 Brest, France; CHU de Brest, 29200 Brest, France; Association Gaétan Saleün, 29200 Brest, France
| | - Chandran Ka
- University Brest, Inserm, EFS, UMR 1078, GGB, 29200 Brest, France; CHU de Brest, 29200 Brest, France; Laboratory of Excellence GR-Ex, 75015 Paris, France
| | - Isabelle Callebaut
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005 Paris, France
| | - Gérald Le Gac
- University Brest, Inserm, EFS, UMR 1078, GGB, 29200 Brest, France; CHU de Brest, 29200 Brest, France; Laboratory of Excellence GR-Ex, 75015 Paris, France.
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Abstract
Haemochromatosis is one of the most common genetic diseases affecting patients of northern European ancestry. It is overdiagnosed in patients without iron overload and is underdiagnosed in many patients. Early diagnosis by genetic testing and therapy by periodic phlebotomy can prevent the most serious complications, which include liver cirrhosis, liver cancer, and death. This Seminar includes an update on the origins of haemochromatosis; and an overview pathophysiology, genetics, natural history, signs and symptoms, differential diagnoses, treatment with phlebotomy, outcomes, and future directions.
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Affiliation(s)
- Paul C Adams
- Department of Medicine, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada.
| | - Gary Jeffrey
- Medical School, University of Western Australia, Perth, WA, Australia
| | - John Ryan
- Royal College of Surgeons of Ireland, Dublin, Ireland
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Magnetic Resonance Liver Iron Concentration Can Guide Venesection Decision-Making in Hyperferritinemia. Dig Dis Sci 2023; 68:2704-2709. [PMID: 36929239 DOI: 10.1007/s10620-023-07873-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 02/09/2023] [Indexed: 03/18/2023]
Abstract
BACKGROUND The clinical benefit of venesection in suspected iron overload can be unclear and serum ferritin may overestimate the degree of iron overload. AIMS To help inform practice, we examined magnetic resonance liver iron concentration (MRLIC) in a cohort investigated for haemochromatosis. METHODS One hundred and six subjects with suspected haemochromatosis underwent HFE genotyping and MRLIC with time-matched serum ferritin and transferrin saturation values. For those treated with venesection, volume of blood removed was calculated as a measure of iron overload. RESULTS Forty-seven C282Y homozygotes had median ferritin 937 µg/l and MRLIC 4.83 mg/g; MRLIC was significantly higher vs non-homozygotes for any given ferritin concentration. No significant difference in MRLIC was observed between homozygotes with and without additional risk factors for hyperferritinemia. Thirty-three compound heterozygotes (C282Y/H63D) had median ferritin 767 µg/l and MRLIC 2.58 mg/g; ferritin < 750 µg/l showed 100% specificity for lack of significant iron overload (< 3.2 mg/g). 79% of C282Y/H63D had additional risk factors-mean MRLIC was significantly lower in this sub-group (2.4 mg/g vs 3.23 mg/g). 26 C282Y heterozygous or wild-type had median ferritin 1226 µg/l and MRLIC 2.13 mg/g; 69% with additional risk factors had significantly higher ferritin concentrations (with comparable MRLIC) and ferritin < 1000 µg/l showed 100% specificity for lack of significant iron overload. In 31 patients (26 homozygotes, 5 C282Y/H63D) venesected to ferritin < 100 µg/l, MRLIC and total venesection volume correlated strongly (r = 0.749), unlike MRLIC and serum ferritin. CONCLUSION MRLIC is an accurate marker of iron overload in haemochromatosis. We propose serum ferritin thresholds in non-homozygotes which, if validated, could tailor cost-effective use of MRLIC in venesection decision-making.
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