The flatiron mutation in mouse ferroportin acts as a dominant negative to cause ferroportin disease

Ferroportin disease is caused by mutation of one allele of the iron exporter ferroportin (Fpn/IREG1/Slc40a1/MTP1). All reported human mutations are missense mutations and heterozygous null mutations in mouse Fpn do not recapitulate the human disease. Here we describe the flatiron (ffe) mouse with a missense mutation (H32R) in Fpn that affects its localization and iron export activity. Similar to human patients with classic ferroportin disease, heterozygous ffe/+ mice present with iron loading of Kupffer cells, high serum ferritin, and low transferrin saturation. In macrophages isolated from ffe/+ heterozygous mice and through the use of Fpn plasmids with the ffe mutation, we show that Fpn(ffe) acts as a dominant negative, preventing wild-type Fpn from localizing on the cell surface and transporting iron. These results demonstrate that mutations in Fpn resulting in protein mislocalization act in a dominant-negative fashion to cause disease, and the Fpn(ffe) mouse represents the first mouse model of ferroportin disease.     

A novel ferroportin mutation in a Canadian family with autosomal dominant hemochromatosis

We report a new mutation, Asn185Asp, in exon 6 of the ferroportin gene (FPN1) in 15 members of three successive generations of a Canadian family of Scandinavian origin with autosomal dominant hemochromatosis. Hyperferritinemia with low transferrin saturation was noted in younger family members, seven of whom were aged 20 years or less at the time of diagnosis. In those individuals first diagnosed with hemochromatosis in later life, marked hyperferritinemia was accompanied by high transferrin saturation. In contrast to the phenotype of high ferritin with low saturation first reported for ferroportin disease, this family demonstrates a phenotype of iron indices that varies with age.     

Autosomal dominant hereditary hemochromatosis associated with a novel ferroportin mutation and unique clinical features

Hereditary hemochromatosis is a common disorder of iron metabolism most frequently associated with mutations in the HFE gene. Hereditary hemochromatosis may be caused by other less common genetic mutations including those in the ferroportin gene. Whereas hereditary hemochromatosis associated with HFE mutations is an autosomal recessive disorder, essentially all cases of hereditary hemochromatosis associated with ferroportin mutations follow an autosomal dominant pattern of inheritance, and most cases are notable for the lack of an elevated transferrin saturation and presence of iron deposition in Kupffer cells. This report describes the clinical and laboratory features of a family with hereditary hemochromatosis associated with a previously unrecognized ferroportin mutation (Cys326Ser). Three generations of the family are described. The disease in this family is notable for young age at onset, elevated transferrin saturation values, and hepatocyte iron deposition. The distinct molecular and clinical features reflect the heterogeneous nature of this disease.     

Phenotypic expression of ferroportin disease in a family with the N144H mutation

Ferroportin is a putative transmembrane channel involved in the exit of iron out of the enterocytes, the macrophages and the hepatocytes. Mutations in the human gene coding ferroportin have been linked to an unusual form of iron overload, now referred to as "hemochromatosis type IV" or "ferroportin disease" characterized by a prevalent iron overload of macrophages and liver Küpffer cells. We report four patients from a same family with ferroportin disease associated with the N144H mutation. We show that in this family the mutation which is fully penetrant, may act through an increased iron export from macrophages as suggested by the unexpected absence of iron overload in the spleen and bone marrow detected by magnetic resonance imaging, that it co-segregates with a phenotype close to the classical form of HFE-associated hemochromatosis and was associated, in the oldest patient, with the development of hepatocellular carcinoma in a non cirrhotic liver. Our findings illustrate the existence of a genotype-phenotype relationship in "ferroportin disease", suggest that MRI may be useful in determining this phenotype and show that hepatocellular carcinoma may occur in these patients even without cirrhosis. This observation justifies careful follow-up of this subgroup of patients.     

A novel mutation in ferroportin1 is associated with haemochromatosis in a Solomon Islands patient

BACKGROUND: A severe form of iron overload with the clinicopathological features of haemochromatosis inherited in an autosomal dominant manner has been described in the Solomon Islands. The genetic basis of the disorder has not been identified. The disorder has similarities to type 4 haemochromatosis, which is caused by mutations in ferroportin1. AIMS: The aims of this study were to identify the genetic basis of iron overload in a patient from the Solomon Islands. PATIENT AND METHODS: Genomic DNA was isolated from peripheral blood leucocytes of a Solomon Islands man with severe iron overload. The entire coding region and splice sites of the ferroportin1 gene was sequenced. RESULTS AND CONCLUSIONS: A novel missense mutation (431A>C; N144T) was identified in exon 5 of the ferroportin1 gene. A novel restriction endonuclease based assay which identifies both the N144T and N144H mutations was developed which will simplify the diagnosis and screening of patients for iron overload in the Solomon Islands and other populations. This is the first identified mutation associated with haemochromatosis in the Solomon Islands population.     

The pathophysiological consequences of somatostatin receptor internalization and resistance

Somatostatin receptors expressed on tumor cells form the rationale for somatostatin analog treatment of patients with somatostatin receptor-positive neuroendocrine tumors. Nevertheless, although somatostatin analogs effectively control hormonal hypersecretion by GH-secreting pituitary adenomas, islet cell tumors, and carcinoid tumors, significant differences are observed among patients with respect to the efficacy of treatment. This may be related to a differential expression of somatostatin receptor subtypes among tumors. In addition, the property of somatostatin receptor subtypes to undergo agonist-induced internalization has important consequences for visualizing, as well as for therapy, of receptor-positive tumors using radioisotope- or chemotherapeutic-compound-coupled somatostatin analogs. This review covers the pathophysiological role of somatostatin receptor subtypes in determining the efficacy of treatment of patients with somatostatin receptor-positive tumors using somatostatin analogs, as well as the preclinical and clinical consequences of agonist-induced receptor internalization for somatostatin receptor-targeted radio- and chemotherapy. Herein, the development and potential role of novel somatostatin analogs is discussed.     

Hepcidin‐dependent and hepcidin‐independent regulation of erythropoiesis in a mouse model of anemia of chronic inflammation

Increased hepcidin antimicrobial peptide correlates with hypoferremia and anemia in various disease states, but its requirement for anemia of inflammation has not been adequately demonstrated. Anemia of inflammation is usually described as normocytic and normochromic, while diseases associated with over expression of hepcidin, alone, are often microcytic and hypochromic. These differences in erythrocyte parameters suggest anemia in many inflammatory states may not be fully explained by hepcidin‐mediated iron sequestration. We used turpentine‐induced sterile abscesses to model chronic inflammation in mice with targeted disruption of Hepcidin 1 [Hepc1 (?/?)] or its positive regulator, Interleukin‐6 [IL‐6 (?/?)], to determine whether these genes are required for features characteristic of anemia of inflammation. Although hemoglobin levels did not decline in Hepc1 (?/?) mice with sterile abscesses, erythrocyte numbers were significantly reduced compared to untreated Hepc1 (?/?) mice. In contrast, both hemoglobin concentration and erythrocyte number declined significantly in wild type and IL‐6 (?/?) mice with sterile abscesses. Both Hepc1 (?/?) and IL‐6 (?/?) mice had increased erythrocyte mean cell volume and mean cell hemoglobin following sterile abscesses, while wild types had no change. Thus, IL‐6 (?/?) mice with sterile abscesses exhibit an intermediate phenotype between wild type and Hepc1 (?/?). Our results demonstrate the requirement of Hepc1 for the development of anemia in this rodent model. Simultaneously, our results demonstrate hepcidin‐independent effects of inflammation on the suppression of erythropoiesis. Our results suggest chronic anemia associated with inflammation may benefit from interventions protecting erythrocyte number in addition to anti‐hepcidin interventions aimed at enhancing iron availability. Am. J. Hematol. 89:470–479, 2014. © 2014 Wiley Periodicals, Inc.     

Autosomal dominant iron overload due to a novel mutation of ferroportin1 associated with parenchymal iron loading and cirrhosis

We report the identification of a novel mutation in ferroportin1 in an Australian family with autosomal dominant iron overload. The phenotype of iron overload in one member of this family is associated with high serum ferritin concentration and elevated transferrin saturation. The pattern of iron overload in the liver shows accumulation predominantly in parenchymal cells with some Kupffer cell iron loading. Although some cases of type 4 haemochromatosis have been associated with the development of liver fibrosis this is the first report of a patient with fully established cirrhosis at a relatively young age (32 years). The coexistence of sarcoidosis in this patient may contribute to the more severe phenotype. This report highlights the phenotypic variability that can occur in type 4 haemochromatosis. Some patients have predominant reticuloendothelial iron loading and normal transferrin saturation whereas others have predominant parenchymal iron loading and elevated transferrin saturation. The reasons for this variability remain to be determined. Interestingly this is the third mutation to affect asparagine 144, reinforcing the important role for this amino acid in the function of ferroportin1.     

Genetic and clinical heterogeneity of ferroportin disease

Ferroportin is encoded by the SLC40A1 gene and mediates iron export from cells by interacting with hepcidin. SLC40A1 gene mutations are associated with an autosomal type of genetic iron overload described as haemochromatosis type 4, or HFE4 (Online Mendelian Inheritance in Man number 606069), or ferroportin disease. We report three families with this condition caused by novel SLC40A1 mutations. Denaturing high-performance liquid chromatography was employed to scan for the SLC40A1 gene. A D181V (A846T) mutation in exon 6 of the ferroportin gene was detected in the affected members of an Italian family and shown to have a de novo origin in a maternal germinal line. This mutation was associated with both parenchymal and reticuloendothelial iron overload in the liver, and with reduced urinary hepcidin excretion. A G80V (G543T) mutation in exon 3 was found in the affected members of an Italian family with autosomal hyperferritinaemia,. Finally, a G267D (G1104A) mutation was identified in exon 7 in a family of Chinese descent whose members presented with isolated hyperferritinaemia. Ferroportin disease represents a protean genetic condition in which the different SLC40A1 mutations appear to be responsible for phenotypic variability. This condition should be considered not only in families with autosomal iron overload or hyperferritinaemia, but also in cases of unexplained hyperferritinaemia.     

A male patient with ferroportin disease B and a female patient with iron overload similar to ferroportin disease B

Reticuloendothelial iron overload is associated with secondary hemochromatosis including repeated transfusions and iron over-supplementation. Ferroportin disease B is a severe subtype of hereditary iron overload syndrome with an activated reticuloendothelial system. The iron exporter ferroportin may be insensitive to hepcidin 25 in this subtype. However, the interactions between the hepcidin–ferroportin system and modifiers of reticuloendothelial iron overload have not yet been elucidated. We describe two patients with iron overload conditions that were compatible with ferroportin disease B, but their genetic backgrounds and habitual states differed. Both patients had diabetes, periportal fibrosis with severe iron deposits in their hepatocytes and Kupffer cells, and adequate levels of circulating hepcidin 25. However, the first patient was heterozygous for a mutation in the FP gene and free from the acquired factors of iron overload, while the second patient was a heavy drinker with a heterozygous mutation in the TFR2 gene and no mutations in the FP gene. The first patient was the second reported case of ferroportin disease B in Japan. Our study on these 2 patients suggests that liver fibrosis associated with compound iron overload of reticuloendothelial cells and hepatocytes may occur via multi-etiological backgrounds.     

Clinical, pathological, and molecular correlates in ferroportin disease: a study of two novel mutations

BACKGROUND/AIMS: Clinico-pathological manifestations of ferroportin (Fpn) disease (FD) are heterogeneous, with some patients presenting with iron overload predominantly in macrophages ("M" phenotype), others predominantly in hepatocytes ("H" phenotype). This appears to reflect functional heterogeneity of Fpn mutants, with loss-of-function generally resulting in the M type. METHODS: Two unrelated probands with "non-HFE" hemochromatosis were screened for Fpn mutations. Mutants were functionally characterized by immunofluorescence microscopy, evaluation of their ability to bind hepcidin and export iron, and by expressing them in zebrafish. RESULTS: Two novel Fpn mutations were identified: I152F in patient-1, presenting with typical M phenotype; and L233P in patient-2, presenting with ambiguous features (massive overload in both macrophages and hepatocytes). Molecular studies suggested loss of function in both cases. The I152F, normally localized on cell membrane and internalized by hepcidin, showed a unique "primary" deficit of iron export capability. The L233P did not appropriately traffic to cell surface. Loss of function was confirmed by expressing both mutants in vivo in zebrafish, resulting in iron limited erythropoiesis. Clinical manifestations were likely enhanced in both patients by non-genetic factors (HCV, alcohol). CONCLUSIONS: The combination of careful review of clinico-pathological data with molecular studies can yield compelling explanations for phenotype heterogeneity in FD.     

A Japanese family with ferroportin disease caused by a novel mutation of SLC40A1 gene: hyperferritinemia associated with a relatively low transferrin saturation of iron

Ferroportin disease, autosomal-dominant reticuloendothelial iron overload, may be more prevalent than hemochromatosis in Japan. Hyperferritinemia of 822 ng/ml with 24.8% transferrin saturation of iron was incidentally noted in a 43-year-old man. His iron overload was selective in Kupffer cells of the liver. Subsequently, his father was found to have asymptomatic hyperferritinemia of 2,283 ng/ml with 62.1% saturation. These affected subjects were heterozygous for 1467A>C (R489S) in SLC40A1, and without other mutations of the hemochromatosis genes. Here, we report a Japanese family with ferroportin disease, characterized by hyperferritinemia with relatively low transferrin saturations of iron.