Diagnosing aceruloplasminemia: navigating through red herrings

A 58-year-old female was found to have hyperferritinemia (Serum ferritin:1683 ng/mL) during work-up for mild normocytic anemia. Transferrin saturation(TSAT) was low-normal. Magnetic resonance imaging (MRI) abdomen showed evidence of hepatic iron deposition. Liver biopsy showed 4 + hepatic iron deposition without any evidence of steatosis or fibrosis. Quantitative liver iron was elevated at 348.3 µmol/g dry liver weight [Reference range(RR): 3-33 µmol/g dry liver weight]. She was presumptively diagnosed with tissue iron overload, cause uncertain. A diagnosis of ferroportin disease (FD) was considered, but the pattern of iron distribution in the liver, mainly within the hepatic parenchyma (rather than in the hepatic Kupffer cells seen in FD), and the presence of anemia (uncommon in FD) made this less likely. She was treated with intermittent phlebotomy for over a decade with poor tolerance due to worsening normocytic to microcytic anemia. A trial of deferasirox was done but it was discontinued after a month due to significant side effects. During the course of treatment, her ferritin level decreased. Over the past 1.5 years, she developed progressively worsening neurocognitive decline. MRI brain showed areas of susceptibility involving basal ganglia, midbrain and cerebellum raising suspicion for metabolic deposition disease. Neuroimaging findings led to testing for serum copper and ceruloplasmin levels which were both found to be severely low. Low serum copper, ceruloplasmin levels and neuroimaging findings led us to consider Wilson disease however prior liver biopsy showing elevated hepatic iron rather than hepatic copper excluded the diagnosis of Wilson disease. After shared decision making, ceruloplasmin gene analysis was not pursued due to patient's preference and prohibitive cost of testing. The diagnosis of aceruloplasminemia was ultimately made. The biochemical triad of hyperferritinemia, low-normal TSAT and microcytic anemia should raise the possibility of aceruloplasminemia. Since neurological manifestations are rare in most inherited iron overload syndromes, neurological symptoms in a patient with tissue iron overload should prompt consideration of aceruloplasminemia as a differential diagnosis.

Comparative analysis of the functional properties of human and mouse ferroportin

Ferroportin (Fpn)-expressed at the plasma membrane of macrophages, enterocytes, and hepatocytes-mediates the transfer of cellular iron into the blood plasma. Under the control of the iron-regulatory hormone hepcidin, Fpn serves a critical role in systemic iron homeostasis. Whereas we have previously characterized human Fpn, a great deal of research in iron homeostasis and disorders utilizes mouse models. By way of example, the flatiron mouse, a model of classical ferroportin disease, bears the mutation H32R in Fpn and is characterized by systemic iron deficiency and macrophage iron retention. The flatiron mouse also appears to exhibit a manganese phenotype, raising the possibility that mouse Fpn serves a role in manganese metabolism. At odds with this observation, we have found that human Fpn does not transport manganese, so we considered the possibility that a species difference could explain this discrepancy. We tested the hypothesis that mouse but not human Fpn can transport manganese and performed a comparative analysis of mouse and human Fpn. We examined the functional properties of human Fpn, mouse Fpn, and mutant mouse Fpn by using radiotracer assays in RNA-injected Xenopus oocytes. We found that neither mouse nor human Fpn transports manganese. Mouse and human Fpn share identical properties with respect to substrate profile, calcium dependence, optimal pH, and hepcidin sensitivity. We have also demonstrated that Fpn is not an ATPase pump. Our findings validate the use of mouse models of ferroportin function in iron homeostasis and disease.

[Management of iron overload during pregnancy and childbirth in a patient with ferroportin disease]

An asymptomatic woman in her early 40s with a history of hyperferritinemia (5,412 ng/ml) was referred to our hospital after repeated phlebotomy for hemosiderosis. She had unexplained hyperferritinemia, low-normal transferrin saturation, and high hepcidin levels, in the absence of iron overload-induced organ injury. She was diagnosed with ferroportin disease based on detection of the SLC40A1 variant SLC40A1 c.485_487del (p.Val162del) on genetic analysis. Her ferritin levels remained stable during pregnancy, and postpartum anemia was successfully treated with 2-week oral iron therapy. Ferroportin disease is characterized by impaired iron export and preferential iron trapping in tissue macrophages. To reduce risk of anemia, a non-aggressive phlebotomy regimen is recommended in patients with ferroportin disease, which shows a milder clinical course compared with other classical hemochromatosis subtypes.

Biology of the iron efflux transporter, ferroportin

Iron, the most common metal in the earth, is also an essential component for almost all living organisms. While these organisms require iron for many biological processes, too much or too little iron itself poses many issues; this is most easily recognized in human beings. The control of body iron levels is thus an important metabolic process which is regulated essentially by controlling the expression, activity and levels of the iron transporter ferroportin. Ferroportin is the only known iron exporter. The function and activity of ferroportin is influenced by its interaction with the iron-regulatory peptide hepcidin, which itself is regulated by many factors. Here we review the current state of understanding of the mechanisms that regulate ferroportin and its function.

Splicing analysis of SLC40A1 missense variations and contribution to hemochromatosis type 4 phenotypes

Hemochromatosis type 4, or ferroportin disease, is considered as the second leading cause of primary iron overload after HFE-related hemochromatosis. The disease, which is predominantly associated with missense variations in the SLC40A1 gene, is characterized by wide clinical heterogeneity. We tested the possibility that some of the reported missense mutations, despite their positions within exons, cause splicing defects. Fifty-eight genetic variants were selected from the literature based on two criteria: a precise description of the nucleotide change and individual evidence of iron overload. The selected variants were investigated by different in silico prediction tools and prioritized for midigene splicing assays. Of the 15 variations tested in vitro, only two were associated with splicing changes. We confirm that the c.1402G>A transition (p.Gly468Ser) disrupts the exon 7 donor site, leading to the use of an exonic cryptic splicing site and the generation of a truncated reading frame. We observed, for the first time, that the p.Gly468Ser substitution has no effect on the ferroportin iron export function. We demonstrate alternative splicing of exon 5 in different cell lines and show that the c.430A>G (p.Asn144Asp) variant promotes exon 5 inclusion. This could be part of a gain-of-function mechanism. We conclude that splicing mutations rarely contribute to hemochromatosis type 4 phenotypes. An in-depth investigation of exon 5 auxiliary splicing sequences may help to elucidate the mechanism by which splicing regulatory proteins regulate the production of the full length SLC40A1 transcript and to clarify its physiological importance.

Genetic iron overload disorders

Due to its pivotal role in orchestrating vital cellular functions and metabolic processes, iron is an essential component of the human body and a main micronutrient in the human diet. However, excess iron causes an increased production of reactive oxygen species leading to cell dysfunction or death, tissue damage and organ disease. Iron overload disorders encompass a wide spectrum of pathological conditions of hereditary or acquired origin. A number of 'iron genes' have been identified as being associated with hereditary iron overload syndromes, the most common of which is hemochromatosis. Although linked to at least five different genes, hemochromatosis is recognized as a unique syndromic entity based on a common pathogenetic mechanism leading to excessive entry of unneeded iron into the bloodstream. In this review, we focus on the pathophysiologic basis and clinical aspects of the most common genetic iron overload syndromes in humans.

Copper Accumulates in Hemosiderins in Livers of Patients with Iron Overload Syndromes

In biology, redox reactions are essential and sometimes harmful, and therefore, iron metabolism is tightly regulated by cuproproteins. Since the state of copper in iron overload syndromes remains unclear, we investigated whether copper metabolism is altered in these syndromes. Eleven patients with iron overload syndromes participated in this study. The clinical diagnoses were aceruloplasminemia (n=2), hemochromatosis (n=5), ferroportin disease (n=2), and receiving excess intravenous iron supplementation (n=2). Liver specimens were analyzed using a light microscope and transmission electron microscope equipped with an X-ray analyzer. In addition to a large amount of iron associated with oxygen and phosphorus, the iron-rich hemosiderins of hepatocytes and Kupffer cells contained small amounts of copper and sulfur, regardless of disease etiology. Two-dimensional imaging clearly showed that cuproproteins were distributed homogenously with iron complexes within hemosiderins. Copper stasis was unlikely in noncirrhotic patients. The enhanced induction of cuproproteins by excess iron may contribute to copper accumulation in hemosiderins. In conclusion, we have demonstrated that copper accumulates in hemosiderins in iron overload conditions, perhaps due to alterations in copper metabolism.