Gastroenterology

Gastroenterology

Volume 140, Issue 7, June 2011, Pages 2056-2063.e1
Gastroenterology

Basic—Liver, Pancreas, and Biliary Tract
Identification of Mutations in SLC40A1 That Affect Ferroportin Function and Phenotype of Human Ferroportin Iron Overload

https://doi.org/10.1053/j.gastro.2011.02.064Get rights and content

Background & Aims

Patients with ferroportin iron overload due to loss-of-function mutations in SLC40A1 have macrophage iron overload, hyperferritinemia, and normal transferrin saturation. In contrast, hepatocellular iron storage, hyperferritinemia, and increased saturation of transferrin are a distinct clinical presentation of ferroportin iron overload that results from SLC40A1 mutations that confer resistance of ferroportin to hepcidin-mediated inactivation.

Methods

SLC40A1 was sequenced in patients from 2 independent pedigrees affected by hepatic iron overload unrelated to HFE. Functions of the ferroportin variants were tested in vitro.

Results

A patient heterozygous for the variant p.W158C in SLC40A1 presented with macrophage iron overload, hyperferritinemia, and normal transferrin saturation. A patient with hepatocellular iron storage, hyperferritinemia, and increased transferrin saturation was heterozygous for p.H507R. Expression of the p.W158C form of ferroportin in 293T cells resulted in defective trafficking to the plasma membrane and reduced iron export activity; the iron export activity of cells that expressed the p.H507R form of ferroportin did not differ from cells that expressed ferroportin without this mutation. The p.H507R of ferroportin localizes normally to the plasma membrane but is resistant to hepcidin-mediated inactivation. Addition of a synthetic peptide derived from ferroportin without these mutations (amino acids 500–518) decreased the inhibitory activity of hepcidin in cells, whereas a peptide from the same region, with p.H507R, had no effect on hepcidin activity.

Conclusions

The variant p.W158C in SLC40A1 impairs intracellular trafficking of ferroportin, resulting in reduced iron export. The variant p.H507R does not bind hepcidin in vitro and results in apparent hepcidin resistance.

Section snippets

Genetic Studies

DNA was extracted from peripheral blood of the patients and unaffected family members. All 8 exons and exon-intron boundaries of SLC40A1 were sequenced in the probands. Samples from family members were evaluated for the presence/absence of mutations identified in probands. A panel of DNA samples from controls was investigated to determine the frequency of novel mutations in the general population. Polymerase chain reaction primers and polymerase chain reaction conditions were as previously

Distinct Phenotypic Presentation of Ferroportin Iron Overload

The index case of family A was a 54-year-old asymptomatic white man who was first referred for further investigation of hyperferritinemia (3015 μg/L) and a transferrin saturation of 21%. At the time of presentation, the patient was in good health; in particular, he had neither joint symptoms nor diabetes. The patient had been successfully treated for ulcerative colitis with mesalazine. His medical history was otherwise unremarkable (Figure 1A).

The index case in family B was a 41-year-old white

Discussion

Here we report on the clinicopathologic manifestations and functional consequences of 2 hitherto unknown human ferroportin variants. It has been proposed that ferroportin iron overload can be readily distinguished from HFE-associated hemochromatosis by a combination of genetic, histologic, and clinical features.1 The genetic characteristics of ferroportin iron overload are its autosomal dominant mode of inheritance and the presence of SLC40A1 mutations, of which 38 distinct variants have so far

Acknowledgments

The authors thank Anna Schlögl, Nadja Baumgartner, and Gisela Egg for excellent technical support.

References (26)

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Conflicts of interest The authors disclose no conflicts.

Funding Supported by the Austrian Science Funds FWF Project P19579 (to H.Z.).

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