Control of iron metabolism – Lessons from neonatal hemochromatosis
Authors: Heinz Zoller, A.S. Knisely
Journal: Journal of Hepatology (2012)

Neonatal iron overload and tissue siderosis due to gestational alloimmune liver diseaseJournal of HepatologyVol. 56Issue 6PreviewGestational alloimmune liver disease is the main cause of the neonatal hemochromatosis phenotype, wherein severe neonatal liver disease is associated with iron overload and extrahepatic tissue siderosis. How fetal liver disease produces extrahepatic siderosis is not known. We hypothesized that fetal liver injury causes deficient hepcidin production and poor regulation of placental iron flux. Under the resulting conditions of iron overload, the tissue pattern of extrahepatic siderosis is determined by the normal expression of proteins involved in the import of non-transferrin-bound iron and the export of cellular iron. Full-Text PDF When hepatologists begin their investigations at the scene of liver damage, iron is certainly on the list of "usual suspects" to be rounded up. Hemochromatosis, a well-known cause of chronic liver disease, is the most prevalent genetic disorder in adults [[1]EASL clinical practice guidelines for HFE hemochromatosis. J Hepatol 2010;53:3–22.Google Scholar]. Serum iron parameters are therefore included in most guidelines on how to investigate patients with elevated transaminases or chronic liver disease [[2]Giboney P.T. Mildly elevated liver transaminase levels in the asymptomatic patient.Am Fam physician. 2005; 71: 1105-1110PubMed Google Scholar]. The hemochromatosis (HFE) genotype is an important piece of evidence in patients with liver disease and elevated transferrin saturation with hyperferritinemia, because homozygosity for the C282Y allele of HFE is considered sufficient to diagnose hemochromatosis under these circumstances [[1]EASL clinical practice guidelines for HFE hemochromatosis. J Hepatol 2010;53:3–22.Google Scholar]. Compound heterozygosity for C282Y and H63D has been almost removed from the watch-list and is currently considered a mere risk factor for liver diseases – sufficient to cause hemochromatosis or even cirrhosis only in combination with other health burdens. Hence, a partner in crime for HFE mutation must be found in patients with liver disease and C282Y/H63D compound heterozygosity [[3]Allen K.J. Gurrin L.C. Constantine C.C. Osborne N.J. Delatycki M.B. Nicoll A.J. et al.Iron-overload-related disease in HFE hereditary hemochromatosis.N Engl J Med. 2008; 358: 221-230Crossref PubMed Scopus (527) Google Scholar]. If there is evidence for iron overload in the absence of hemochromatosis-associated HFE genotypes and the hepatopathologist finds iron confined to hepatocytes, sharp investigators are well advised to search for the culprit in the genes encoding transferrin receptor 2 (TFR2) and ferroportin (SLC40A1) or even to hunt for combined mutations in these genes if a patient presents with severe iron overload or early-onset disease [[4]Fleming R.E. Ponka P. Iron overload in human disease.N Engl J Med. 2012; 366: 348-359Crossref PubMed Scopus (415) Google Scholar]. If the patient is adolescent or before the 3rd decade of life and presents with heart failure or hypogonadism in addition to – often overlooked – liver disease, other genes will be committed in custody. Mutations in HJV and HAMP, which respectively encode hemojuvelin and hepcidin, will be sufficient to identify juvenile hemochromatosis [[5]Pietrangelo A. Juvenile hemochromatosis.J Hepatol. 2006; 45: 892-894Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar]. Through the power of genetics, iron-related diseases are now subject to close scrutiny. In addition, genetic studies have greatly advanced our understanding of hemochromatosis. This progress is reflected in the proposed re-classification of human iron overload in which deficiency of the iron hormone hepcidin is the unifying feature of all disorders with hepatocellular iron accumulation [[6]Pietrangelo A. Hemochromatosis: an endocrine liver disease.Hepatology. 2007; 46: 1291-1301Crossref PubMed Scopus (164) Google Scholar]. Primary hepcidin deficiency results from mutation in HAMP. Secondary hepcidin deficiency is found in patients with mutations in HFE, TFR2, or HJV. Deficiency in the effects of hepcidin, or resistance to hepcidin's effects, through certain SLC40A1 mutations can be an alternative cause of hepatocellular iron overload [7Mayr R. Griffiths W.J. Hermann M. McFarlane I. Halsall D.J. Finkenstedt A. et al.Identification of mutations in SLC40A1 that affect ferroportin function and phenotype of human ferroportin iron overload.Gastroenterology. 2011; 140 (e2051): 2056-2063Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar, 8Ludwig J. Hashimoto E. Porayko M.K. Moyer T.P. Baldus W.P. Hemosiderosis in cirrhosis: a study of 447 native livers.Gastroenterology. 1997; 112: 882-888Abstract Full Text Full Text PDF PubMed Scopus (247) Google Scholar]. Like genetic syndromes causing hepcidin alterations, acquired conditions can also result in hepcidin deficiency or hepcidin resistance. Liver dysfunction non-specifically causes hepcidin deficiency, which explains the iron overload frequent in end-stage liver disease. Finally, recent studies suggest that in patients with dysmetabolic iron overload syndrome, acquired hepcidin resistance is involved in the pathogenesis of iron loading [[9]Zimmermann A. Zimmermann T. Schattenberg J. Pottgen S. Lotz J. Rossmann H. et al.Alterations in lipid, carbohydrate and iron metabolism in patients with non-alcoholic steatohepatitis (NASH) and metabolic syndrome.Eur J Intern Med. 2011; 22: 305-310Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar]. This new classification of adult and juvenile as genetic or acquired hemochromatosis – hepcidin-deficient or hepcidin-resistant – embraces all iron overload syndromes except neonatal hemochromatosis (NH). Despite its high recurrence rate in siblings of affected patients, this disorder has evaded genetic reconnaissance [[10]Cox T.M. Halsall D.J. Hemochromatosis-neonatal and young subjects.Blood Cells Mol Dis. 2002; 29: 411-417Crossref PubMed Scopus (30) Google Scholar]. NH until recently was an enigmatic condition in which affected patients typically present with liver failure during their first days of postnatal life and on histopathologic study exhibit siderosis of epithelia (most prominently of acini of minor salivary glands, thyroid, and pancreas) and of myocardium, with at worst scant reticuloendothelial-cell siderosis. An antioxidant cocktail with iron chelators is a small hope for cure or may help to bridge the time to liver transplantation in this usually fatal disorder [[11]Flynn D.M. Mohan N. McKiernan P. Beath S. Buckels J. Mayer D. et al.Progress in treatment and outcome for children with neonatal haemochromatosis.Arch Dis Child Fetal Neonatal Ed. 2003; 88: F124-F127Crossref PubMed Google Scholar]. Recurrence of NH after liver transplantation has not been described (Fig. 1). Findings reported in this issue of the Journal of Hepatology now position NH within the matrix of a hepcidin-based hemochromatosis classification, lodging it in the 'acquired hepcidin deficiency' group. This is one major implication of the findings from Silvana Bonilla, Joshua D. Prozialeck and their team from Peter Whitington's group at Chicago's Northwestern University [[12]Bonilla S. Prozialeck J.D. Malladi P. Pan X. Yu S. Melin-Aldana H. et al.Neonatal iron overload and tissue siderosis due to gestational alloimmune liver disease.J Hepatol. 2012; 56: 1351-1355Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar]. They report the expression of iron genes in various tissues from a small series of patients with neonatal liver failure, all of whom had a sibling with histologically proven NH. The expression of hepcidin, the main iron regulatory peptide, in livers from infants with NH was <20% of that in normal neonatal liver tissue, which provides a clue to the pathogenesis of NH. As in adult and juvenile hemochromatosis, where hepcidin deficiency is believed to mediate increased absorption of dietary iron, hepcidin deficiency in NH might be expected to dysregulate transfer of iron across the placenta, which is equipped with the same iron transporters as the gut. Evidence from the hepcidin knockout mouse shows that hepcidin modulates iron transport across the placenta [[13]Nicolas G. Bennoun M. Porteu A. Mativet S. Beaumont C. Grandchamp B. et al.Severe iron deficiency anemia in transgenic mice expressing liver hepcidin.Proc Natl Acad Sci USA. 2002; 99: 4596-4601Crossref PubMed Scopus (760) Google Scholar] although hepcidin deficiency is not known to cause fetal liver disease and, indeed, iron overload in hepcidin-deficient mice appears to be a postnatal phenomenon [[14]Lesbordes-Brion J.C. Viatte L. Bennoun M. Lou D.Q. Ramey G. Houbron C. et al.Targeted disruption of the hepcidin 1 gene results in severe hemochromatosis.Blood. 2006; 108: 1402-1405Crossref PubMed Scopus (199) Google Scholar]. Iron is transferred across the placenta through the hepcidin receptor ferroportin, which releases ferrous iron. After oxidation of ferrous iron by ceruloplasmin, the metal is bound by transferrin. Transferrin, which is – like hepcidin – mainly produced in the liver, is also significantly reduced in NH. Hypotransferrinemia, perhaps potentiated by increased transplacental iron transfer, in a toxic alliance with reduced fetal hepcidin, results in increased non-transferrin-bound iron (NTBI). NTBI is implicated in the hemochromatotic siderosis of atransferrinemia [15Bernstein S.E. Hereditary hypotransferrinemia with hemosiderosis, a murine disorder resembling human atransferrinemia.J Lab Clin Med. 1987; 110: 690-705PubMed Google Scholar, 16Craven C.M. Alexander J. Eldridge M. Kushner J.P. Bernstein S. Kaplan J. Tissue distribution and clearance kinetics of non-transferrin-bound iron in the hypotransferrinemic mouse: a rodent model for hemochromatosis.Proc Natl Acad Sci USA. 1987; 84: 3457-3461Crossref PubMed Scopus (219) Google Scholar], a condition in which hepcidin handling has not been studied. Are NTBI concentrations elevated in fetuses and infants with NH? An anecdotal report suggests that they may be [[17]Knisely A.S. Grady R.W. Kramer E.E. Jones R.L. Cytoferrin, maternofetal iron transport, and neonatal hemochromatosis.Am J Clin Pathol. 1989; 92: 755-759PubMed Google Scholar]. Determinations of NTBI [[18]Singh S. Hider R.C. Porter J.B. A direct method for quantification of non-transferrin-bound iron.Anal Biochem. 1990; 186: 320-323Crossref PubMed Scopus (135) Google Scholar] nowadays approaching the clinical routine [[19]Prezelj M. Knap B. Automated assay for non-transferrin-bound iron in serum samples.Clin Chem Lab Med. 2010; 48: 1427-1432Crossref PubMed Google Scholar] are yet to be performed systematically in NH patients. Nor has plasma hepcidin been quantitated in such patients. To explain the distinct pattern of iron overload in NH, the Northwestern University investigators further assessed iron transport protein expression in extrahepatic tissues of affected infants and control tissue. Tissues most severely iron-loaded in NH, such as epithelium of pancreatic acini or thyroid follicles, stained strongly for the metal transport protein ZIP14, encoded by SLC39A14, but did not mark substantially for the iron export protein ferroportin. Further evidence in support of ZIP14 as an iron transporter of importance came from co-localization studies showing that cells with increased stainable iron express ZIP14. The interplay between ZIP14 and NTBI remains unclear [[12]Bonilla S. Prozialeck J.D. Malladi P. Pan X. Yu S. Melin-Aldana H. et al.Neonatal iron overload and tissue siderosis due to gestational alloimmune liver disease.J Hepatol. 2012; 56: 1351-1355Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar]. Case closed? Perhaps not. One must bear in mind that this study was limited to patients with gestational alloimmune liver disease (GALD)-associated NH (GALD-NH). Immunohistochemical analysis of liver of affected infants showed deposition of complement factors as pathognomonic in GALD [[20]Whitington P.F. Pan X. Kelly S. Melin-Aldana H. Malladi P. Gestational alloimmune liver disease in cases of fetal death.J Pediatr. 2011; 159: 612-616Abstract Full Text Full Text PDF PubMed Scopus (37) Google Scholar]. Based on the hypothesis that NH is generally caused by maternal antibodies against a fetal liver antigen, administration of intravenous immunoglobulin has been shown to ameliorate or even to prevent recurrence of NH within sibships [[21]Whitington P.F. Hibbard J.U. High-dose immunoglobulin during pregnancy for recurrent neonatal haemochromatosis.Lancet. 2004; 364: 1690-1698Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar]. GALD might be one of the commonest causes of NH, but a phenotype of neonatal liver failure with significant hepatic and extrahepatic iron overload is not exclusive to GALD-NH. Mitochondrial DNA depletion syndromes [22Pronicka E. Weglewska-Jurkiewicz A. Taybert J. Pronicki M. Szymanska-Debinska T. Karkucinska-Wieckowska A. et al.Post mortem identification of deoxyguanosine kinase (DGUOK) gene mutations combined with impaired glucose homeostasis and iron overload features in four infants with severe progressive liver failure.J Appl Genet. 2011; 52: 61-66Crossref PubMed Scopus (38) Google Scholar, 23Hanchard N.A. Shchelochkov O.A. Roy A. Wiszniewska J. Wang J. Popek E.J. et al.Deoxyguanosine kinase deficiency presenting as neonatal hemochromatosis.Mol Genet Metab. 2011; 103: 262-267Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar] or Down syndrome with megakaryocytic transient myeloproliferative disorder [24Miyauchi J. Ito Y. Kawano T. Tsunematsu Y. Shimizu K. Unusual diffuse liver fibrosis accompanying transient myeloproliferative disorder in Down's syndrome: a report of four autopsy cases and proposal of a hypothesis.Blood. 1992; 80: 1521-1527PubMed Google Scholar, 25Ruchelli E.D. Uri A. Dimmick J.E. Bove K.E. Huff D.S. Duncan L.M. et al.Severe perinatal liver disease and Down syndrome: an apparent relationship.Hum Pathol. 1991; 22: 1274-1280Abstract Full Text PDF PubMed Scopus (74) Google Scholar] also are associated with a NH phenotype. These findings support the hypothesis that any genetic, immunological or metabolic defect that causes intrauterine liver failure will result in both hypotransferrinemia and low fetal hepcidin expression, perhaps with dysregulated iron transfer across the placenta from the mother to the fetus. Support for this hypothesis comes from reports of infants with NH whose mothers developed severe and refractory gestational iron deficiency [[26]Kelly A.L. Lunt P.W. Rodrigues F. Berry P.J. Flynn D.M. McKiernan P.J. et al.Classification and genetic features of neonatal haemochromatosis: a study of 27 affected pedigrees and molecular analysis of genes implicated in iron metabolism.J Med Genet. 2001; 38: 599-610Crossref PubMed Scopus (94) Google Scholar]; in contrast, however, are findings in earlier quantitative work indicating that redistribution of iron within the conceptus – away from the liver and into other sites – rather than absolute iron overload is found in NH [[27]Silver M.M. Valberg L.S. Cutz E. Lines L.D. Phillips M.J. Hepatic morphology and iron quantitation in perinatal hemochromatosis. Comparison with a large perinatal control population, including cases with chronic liver disease.Am J Pathol. 1993; 143: 1312-1325PubMed Google Scholar]. Is NH therefore a final common manifestation of intrauterine liver failure rather than a defined disease entity? This would explain why it has been impossible to identify a genetic cause of NH [[10]Cox T.M. Halsall D.J. Hemochromatosis-neonatal and young subjects.Blood Cells Mol Dis. 2002; 29: 411-417Crossref PubMed Scopus (30) Google Scholar] or even to define a clear mode of inheritance. NH is a devastating condition. Progress in treatment and prevention of NH also includes improving the diagnosis. Findings reported here suggest a model in which fetal hepcidin deficiency contributes to NH. Novel therapeutic developments could therefore aim at reducing transplacental iron transport or aim at supplementing fetal hepcidin – possibly with recently developed mini-hepcidins [[28]Preza G.C. Ruchala P. Pinon R. Ramos E. Qiao B. Peralta M.A. et al.Minihepcidins are rationally designed small peptides that mimic hepcidin activity in mice and may be useful for the treatment of iron overload.J Clin Invest. 2011; 121: 4880-4888Crossref PubMed Scopus (167) Google Scholar]. The most immediate implications, however, of recent developments and current findings regarding NH in clinical practice are probably that NH is better recognized as a syndrome rather than as an independent entity and that physicians and researchers involved in the care of NH patients and affected families must continue investigations to identify the underlying cause of liver failure to improve patient care and for correct counseling. Quantitative studies of NTBI and hepcidin levels in NH, for instance, will be of considerable value in understanding the abnormalities in iron handling that mark the disorder. Beyond basic research, accurate diagnosis of underlying conditions is important. GALD, mitochondrial DNA depletion syndromes and inborn errors of metabolism or hemopoiesis associated with liver failure all may incite NH. Each condition has a specific prognosis, recurrence rate, mode of inheritance and management. Pediatric hepatologists and genetic counselors are therefore well advised not to conclude their investigations when 'NH' is diagnosed in an infant. To do so risks arresting only the 'hitman' and not the 'true offender'. The authors declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.