Neonatal Hemochromatosis

CLINICAL PRESENTATION

When not stillborn, infants with NH frequently are premature or are small for gestational age. The pregnancy may be complicated by intrauterine growth retardation, oligohydramnios, placental edema, or sometimes polyhydramnios.^6,,7 Illness usually is evident within hours of birth, although some have been diagnosed at a few weeks of age.^6,,8 Patients have features of liver failure with hypoalbuminemia, hypoglycemia, coagulopathy, low fibrinogen, and, frequently, thrombocytopenia and anemia. If not present at birth, ascites develops shortly thereafter, as does hyperbilirubinemia. Transaminase levels are characteristically low.

Clearly, the onset of the liver disease is in utero, with end-stage liver disease already established even in the prematurely born infant. Hepatocellular synthetic insufficiency can explain the coagulopathy, low fibrinogen, and hypoalbuminemia. The hypoalbuminemia in turn contributes to a low intravascular oncotic pressure, edema, contracted blood volume, oliguria, and resultant oligohydramnios.⁷The edema and ascites may be attributable to anemia, heart failure, or portal hypertension. The characteristically low transaminases and hypoglycemia that is secondary to poor glycogen stores are evidence of overall hepatocellular loss. The frequently seen anemia probably is multifactorial, caused by severely limited hepatic erythropoiesis, acquired defects in erythrocyte membranes as a result of liver disease, and hypotransferrinemia and low erythropoietin levels as a result of hepatocellular synthetic insufficiency.

OTHER CLINICAL ASSOCIATIONS

The NH phenotype, with respect to clinical presentation, laboratory abnormalities, liver histology, and parenchymal iron deposition, also has been seen in children who ultimately are diagnosed with Δ⁴-3-oxosteroid 5β-reductase deficiency, a defect in bile acid synthesis.^8,,9 Clayton¹⁰pointed out, however, that this enzyme is labile, and, hence, its activity may be substantially reduced with hepatocyte damage. Consequently, Δ⁴-3-oxosteroid 5β-reductase deficiency may or may not be a primary diagnosis in a subset of NH patients. A report of an infant with NH born to a mother with Sjögren's syndrome and high levels of anti-Ro/SS-A and anti-La/SS-B antibodies raises the possibility of an autoimmune pathophysiology to this condition.¹¹

Most patients with NH do not have other significant congenital abnormalities; however, patients with 2 separate syndromes have been described with some frequency. Four children, 2 pairs of siblings, have been reported with trichomalacia, diarrhea, facial dysmorphology, and some degree of congenital heart disease; Verloes and colleagues^12–14 coined the name “Tricho-Hepato-Enteric syndrome.” In addition, 4 patients have been described with NH and renal tubular dysgenesis, also an autosomal recessive condition.^15,,16 This supports the belief that NH is the result of an in utero insult to the fetus.

GENETICS

Family analyses have been conducted to determine whether there is a genetic basis for NH and whether there is a genetic link to hereditary hemochromatosis. Transmission of the disorder has been described as autosomal recessive, codominant, and autosomal dominant with variable penetrance. There now are multiple reports of recurrence of NH in siblings^17–19 and half-siblings.²⁰In most analyses of family occurrences, an autosomal recessive pattern of inheritance has emerged.^18,,19,21 Another observation, however, cannot be ignored. Several women have had infants with NH fathered by different men, yet no man has fathered children with NH with different women. This suggests possible mitochondrial inheritance, an acquired and persistent maternal factor, or gonadal mosaicism for a dominant mutation lethal in spermatogenesis but not in oogenesis.²²

A genetic relationship with hereditary hemochromatosis is an attractive idea because the distribution of parenchymal iron and the liver histology in the 2 conditions are similar. The HFE (hereditary hemochromatosis) gene is mutated in the majority of patients with hereditary hemochromatosis. This gene is located on the short arm of chromosome 6, and there is an association with the HLA-A3 alloantigen. The HFE gene mutation has been found in parents of children with NH,²³ and parents and affected children may share the HLA-A3 alloantigen.^17,,19,24,25 Other studies have disputed this link and association, however.²⁶ Furthermore, infants with the HFE gene mutation do not necessarily have NH.²⁷

IRON METABOLISM

The bulk of the body's iron is as essential iron, specifically heme compounds: enzymes with iron-sulfur complexes. The largest store of essential iron is erythron in red blood cells, the next-largest fraction is as myoglobin in muscle, and the third largest fraction is as mitochondrial enzymes.²⁸ These iron fractions are essential for body functioning. Iron in these forms is relatively stable, limited by the life span of the cells in which it is contained.

Tissue iron is stored primarily in ferritin. Ferritin is a polypeptide sphere that encloses iron atoms. Ferritin is found in cellular cytoplasm and lysosomal membranes. Glycosylated, iron-free ferritin is secreted into the serum from all ferritin-producing cells and therefore reflects tissue iron stores. Ferritin secretion into serum increases, however, under conditions of inflammation, particularly when the inflammation involves ferritin-rich tissues. In lysosomes, the ferritin molecules aggregate and the degraded polypeptides and iron coalesce into hemosiderin, which can be seen with Prussian Blue staining under light microscopy.²⁸

Transferrin, the main molecule that mediates transfer of iron between tissues, is a single polypeptide with 2 iron-binding sites. Occupation of none (apoferric), 1 (monoferric), or both (diferric) of the iron-binding sites determines the degree of iron saturation. Transfer of the iron to tissues occurs by the interaction of the transferrin-iron complex with specific membrane receptors and subsequent internalization of the transferrin-iron complex.²⁸ Fibroblasts from patients with NH synthesize ferritin and transferrin receptors, and iron regulates the cellular expression of ferritin and transferrin receptors to the same degree as do fibroblasts from individuals without NH.²⁴ Furthermore, the intracellular processes by which iron is metabolized are unaffected in NH fibroblasts.²⁴ It is known now that the transferrin receptor interacts with both HFE (hereditary hemochromatosis) protein and β2-microglobulin (β2M).²⁹ Proper interaction of these molecules allows for regulated internalization and subsequent cycling back to the cell surface of the transferrin–iron–HFE protein–β2M complex, therefore maintaining correct tissue-iron concentrations. In hereditary hemochromatosis, mutation of the HFE gene results in an abnormal HFE protein that does not associate with β2M and after internalization is not transported back to the cell surface.³⁰ HFE protein is expressed in the crypt cells of the small intestine. It is believed that in individuals with homozygosity for specific HFE gene mutations (C282Y and H63D), the mutant HFE is trapped extracellularly, hence impeding the transport of iron via the transferrin-transferrin receptor interaction.³¹ Parkkila et al²⁹ found that the transferrin receptor and HFE protein–β2M complex also are located in the apical plasma membrane of the syncytiotrophoblast cells of the fetal placenta, thus playing a role in iron transport across the placenta. Placental iron levels, in turn, may regulate the expression of transferrin receptors on the syncytiotrophoblast apical plasma membrane and therefore maintains steady iron uptake into the placenta.³²

Nontransferrin-bound iron (NTBI) ligands also may play a role in hemochromatosis. In hereditary hemochromatosis, a chelator-inaccessible fraction of NTBI has been observed.³³ The identity of this presumably high-affinity ligand has not yet been elucidated. In the case of hemochromatosis, it is possible that this NTBI-ligand fraction is extruded from the cytoplasm of damaged cells. Cytoferrin (host-associated iron transfer factor), an iron-binding compound of lower molecular weight than transferrin, is found mainly in cellular cytoplasm but also in low concentrations in serum. Cytoferrin concentrations are known to increase with liver disease or in the setting of iron loading.³⁴ Knisely et al³⁴compared the serum concentration of cytoferrin among adult nonselected women, parturient women, normal infants (cord serum), and an infant with NH. The difference between parturient and nonparturient women was not significant. Cord sera from normal neonates, however, had a cytoferrin concentration twice that of the women, and sera from the NH infant had a concentration 270 times that of the women. The transplacental gradient of cytoferrin suggests that this compound may be involved in maternofetal transport of iron. The dramatic increase in cytoferrin in the NH neonate simply may be secondary to the liver disease, but its possible role in this disorder warrants additional investigation.

DIAGNOSIS

Diagnosis generally is made after other causes of neonatal liver failure are excluded (Table 1) and confirmatory tests are performed. Serum concentrations of ferritin are elevated in patients with NH; thus, an elevated ferritin will help to confirm the diagnosis. Body-iron stores normally are high in infancy; furthermore, elevated ferritin is nonspecific and simply may represent total body overload, nonspecific liver disease, or inflammation.^7,,35 When measured, the iron-binding capacity (transferrin) is low, reflecting the impaired synthetic ability of the liver. The percentage of iron saturation, however, has been reported markedly to exceed the normally high saturation seen in the cord blood of newborns without liver disease (80%),⁷ with saturations of 95% to 100% common.^6,,7

Siderosis of the liver is normal in the third trimester but can be distinguished from NH hepatic siderosis by the extrahepatic siderosis with reticuloendothelial sparing. Specifically, although the iron deposition in NH is most notable in the liver, it also is present in the heart, pancreas, exocrine and endocrine organs, intestines, and gastric and salivary glands. The siderosis explicitly spares the reticuloendothelial elements, however, as it does in hereditary hemochromatosis. Siderosis of extrahepatic sites including the salivary glands makes it possible to verify the diagnosis histologically without the need for a liver biopsy. Knisely et al³⁶ showed that siderosis of acinar epithelial cells was found in the minor salivary glands of all patients who proved to have NH and none of 30 patients without liver disease. Salivary gland siderosis also was seen in patients with tyrosinemia, parvovirus B19, rubella, α-thalassemia, and renal-hepatic-pancreatic cystic dysplasia of Ivemark, but these generally could be distinguished on other clinical and laboratory grounds.

Because of the paramagnetic influence of ferric ions (Fe³⁺) on the image signal during magnetic resonance imaging (MRI), MRI can be useful in the diagnostic evaluation of an infant with possible NH. The signal alterations caused by the ferric ions cause shortening of the T1 and, more impressive, the T2 relaxation times. Any tissue containing iron therefore will have low signal intensity. In NH with T2-weighted images, the signal intensity of the liver and pancreas will be lower than that of the normal-intensity spleen.³⁷ Furthermore, the more rapid imaging possible with T2 gradient-recalled-echo can be used for morphologic and functional assessment of myocardial siderosis.³⁷ In situations in which a fetus is at risk of having NH, MRI also can be used to evaluate the infant during the third trimester of pregnancy. In this case, fetal liver intensity can be compared with other fetal tissues and with the mother's liver.³⁷

LIVER HISTOLOGY

Nodular cirrhosis with severe cholestasis typically is found at the time of biopsy or autopsy. It is not unusual to see regenerating nodules separated by wide bands of bland fibrosis containing proliferating bile ducts and multinucleated giant cells.^38,,39 Central vein sclerosis with thickened venular walls and lumens either stenosed or occluded by fibrous tissue also is common. The siderosis is always, by definition, significant. Within tubular hepatocytes, hemosiderin occupies the apical cytoplasm adjacent to the bile canaliculi.³⁹ In hepatic giant cells, the iron and bile are more diffusely distributed.³⁹ Extramedullary erythropoiesis, usually obviously apparent in the neonate, is found only in the sinusoids of liver nodules in NH³⁹ and probably contributes to the anemia in these patients. Although less common, hepatocellular carcinoma has been reported in cases of NH at the time of transplantation or autopsy,^38,40–42reinforcing the prenatal onset of this condition.

Whereas the average liver weight is lower in NH than normal livers (reflecting loss of hepatic parenchyma) even when adjustments are made for gestational age and body size, the mean hepatic iron concentration is higher in NH than comparable controls.³⁹Knisely⁷ found that the range of hepatic iron concentration in patients with NH ranged from 240 to 38 200 μg/g dry weight compared with the average weight of that of a healthy neonate (250 μg/g dry weight). It must be noted, however, that despite the clearly elevated liver iron in most cases, the range overlaps with normal perinatal hepatic iron concentration in some patients. Furthermore, there are conditions other than NH in which the iron content is elevated in the liver and other nonreticuloendothelial organs (Table 2). This elevated iron content in other organs is particularly likely with cirrhosis and may indicate a shunt siderosis similar to that frequently seen in adult liver disease.³⁹

TREATMENT AND PROGNOSIS

NH is nearly universally fatal, and experience with treatment is limited because many die before diagnosis. Deferoxamine therapy is not efficacious,^38,,43 and it has been suggested that its use may potentiate bacterial growth.⁶ Despite early preliminary reports to the contrary,^44,,45 deferoxamine combined with an antioxidant cocktail has not proved to be universally successful.

Although experience is very limited, liver transplantation has been successful in treating NH.⁴⁶ In one study of 14 infants with NH treated with an antioxidant cocktail, 5 patients survived to transplantation and 3 were alive 1 year after transplantation.⁶ In most cases, the iron overload resolves slowly after transplantation. In 1 patient, however, iron accumulated in the allograft as early as 7 days posttransplantation and the patient died of cardiac arrhythmias 2 months posttransplantation.⁴² The iron accumulation in the allograft liver was thought to be secondary to redistribution of the preexisting body iron, and the authors speculated that deferoxamine and antioxidant therapy may be beneficial after transplantation.