Neonatal hemochromatosis (NH) is clinically defined as severe neonatal liver disease
in association with extrahepatic siderosis in a distribution similar to that seen
in hereditary hemochromatosis.[1]
[2]
[3]
[4] Considerable evidence indicates that it is a gestational disease in which fetal
liver injury is the dominant feature. Because of the abnormal accumulation of iron
in liver and other tissues, it has been called neonatal iron storage disease, and because of its origins before birth, it has also been called congenital hemochromatosis. Until recently, there has been little understanding of the pathophysiology of NH
including the mechanism of fetal liver injury. There is no evidence that NH is anyway
related to the family of diseases that fall under the classification of hereditary hemochromatosis. Our recent investigations have provided evidence that many cases of NH are due to
maternal alloimmunity directed at the fetal liver. Given the pathology of the liver
and the mechanism of liver injury, NH could best be classified as congenital alloimmune hepatitis.
ETIOLOGY AND PATHOGENESIS
ETIOLOGY AND PATHOGENESIS
The name hemochromatosis implies that iron is involved in the pathogenesis of NH. Thus, a brief overview of
the regulation of fetal iron homeostasis is indicated. The fetus regulates placental
iron transport to ensure adequate iron for the growth and oxygen-carrying capacity
needs of the fetus and newborn. The placenta acts as an active interface between the
mother's huge iron pool and the highly controlled and relatively small fetal iron
pool, ensuring adequate iron supply to the fetus and protecting against potentially
toxic iron overload.[5] Concepts regarding how the flux of iron from mother to fetus is regulated are currently
unfolding. It appears that many of the control mechanisms that function after birth
to control accrual of dietary iron (see review by Fleming and Bacon[6]) also function during fetal life, with the placental trophoblast functioning in
analogy to the duodenal mucosa.[7] Ferroportin is highly expressed and colocalizes with hemochromatosis gene product
(HFE) in placental trophoblast cells.[8]
[9] Ferroportin expression increases with gestational age in parallel with increasing
iron needs of the fetus.[9] Fetal hepcidin evidently regulates fetal iron stores. Disruption of the hepcidin
gene in the mouse results in a hemochromatosis phenotype,[10] and transgenic hepcidin-overexpressing mice are born profoundly anemic and iron-deficient.[11]
NH almost certainly does not result from iron overload. In contrast with hereditary
hemochromatosis where iron overload is the primary event leading to liver injury developing
over many years, it seems implausible that the severe liver injury observed in NH
could be the result of iron overload taking place over only weeks of time. Furthermore,
it has been suggested from clinical observations that liver disease appears to precede
iron deposition in NH.[12]
[13]
[14] This degree of liver injury is not observed in juvenile hereditary hemochromatosis
despite hepatic siderosis that is more severe than that seen in NH.[15]
[16] Juvenile hereditary hemochromatosis results from homozygous mutations in the genes
for hemojuvelin or hepcidin, which in either case results in failure to express hepcidin.[17] Affected individuals would be expected to accumulate excess iron in utero just as the hepcidin knockout mice do, yet none have been described with neonatal
liver disease. In addition, hepcidin knockout mice have no liver injury despite massive
iron overload.[10] This and other evidence speaks strongly against iron overload being the primary
event in the pathogenesis of NH.
It is not clear if iron overload results from liver injury in NH, indeed if it exists
at all. Most cases show clear extrahepatic siderosis, a diagnostic hallmark of NH,
and many have elevated serum iron indices. Yet, many affected babies are anemic. It
is not known if newborns with NH are actually iron-loaded, which is to say that total
body iron content has never been determined. In this model of disease where fetal
liver injury is the primary insult, the hemochromatosis phenotype likely results from
secondary iron deposition in extrahepatic tissues. There are two possibilities to
consider in regard to the mechanism of siderosis in NH. The first possibility is that
the fetus becomes iron-loaded due to poor control of iron flux across the placenta.
Fetal hepcidin is involved in regulating placental ferroportin function, which is
intimately involved in regulating maternal-fetal iron flux. It is reasonable to speculate
that reduced hepcidin synthesis in the severely injured liver could lead to poor regulation
of ferroportin in the placenta and to iron overload. The failure to regulate ferroportin
could also contribute to the observed lack of macrophage and Kupffer cell iron. The
second possibility is that the NH fetus is not actually iron-loaded but rather has
an abnormal but discrete deposition of iron in certain tissues. With severe liver
injury, the central repository and distribution apparatus for iron in the fetus is
impaired. The transferrin saturation is high in NH, so free (non-transferrin-bound)
iron may be in excess. The tissues showing siderosis are those with a propensity to
take up non-transferrin-bound iron from plasma. These mechanisms and possibly others
deserve study.
The cause of fetal liver injury leading to the NH phenotype remains a point of debate.
There is mounting evidence, however, in support of the hypothesis that most cases
result from alloimmune liver injury.[18] The observation leading to the alloimmune hypothesis comes from the unusual pattern
and high rate of recurrence in the progeny of affected women. After the index case,
there is an ∼60% to 80% probability that each subsequent baby born to that mother
will be affected.[19]
[20]
[21] A woman may have unaffected offspring before having the first child with NH, but
thereafter most pregnancies terminate in either a fetal loss or a child born with
NH. There are several documented instances of a woman giving birth to affected babies
with different male parentage, but not vice versa.[19]
[21]
[22] It has never been recorded that female siblings of women having a baby with NH themselves
have had an affected baby. NH appears therefore to be congenital and familial but
not hereditary. This pattern of recurrence is much like that of known materno-fetal
alloimmune diseases.
The alloimmune hypothesis states that NH is an alloimmune gestational disease that
leads to severe fetal liver injury and consequently to the NH phenotype.[18] Materno-fetal alloimmunity is mediated by IgG. Maternal antibodies of the IgG class
(and only IgG) are actively transported across the placenta to the fetus from about
the 18th week of gestation. The principle function of this process is to provide humoral
immunity for the fetus and newborn against a broad array of microbiologic antigens
to which there has been no exposure. The principle of alloimmunity involves exposure
of a woman to a fetal antigen that she fails to recognize as “self,” which results
in sensitization and production of specific immunoglobulin of the IgG class capable
of recognizing and binding to the antigen. In NH, the alloimmune target appears to
be a hepatocyte cell surface antigen. In NH-sensitized mothers, transplacental passage
of maternal IgG to the fetus (in this and subsequent pregnancies) is accompanied by
movement of anti-fetal liver antigen IgG to the fetal circulation, where it binds
to the liver antigen and results in immune injury of the fetal liver.
We have examined this mechanism of fetal liver injury in a mouse model.[23] It is known that human IgG administered by intraperitoneal injection to pregnant
mice from midgestation forward is substantially transferred to the pups. In this model
of passive alloimmunity, pregnant mice received injections of whole serum or IgG from
women whose babies had bona fide NH. Compared with those injected with control sera,
which were not different from saline-injected animals, injecting NH material resulted
in markedly reduced litter size and increased numbers of stillbirths. Liver histology
from E16 to P1 pups showed extensive hepatocyte injury/necrosis and increased lobular
inflammation. No other organs or tissues were damaged. Excess iron could not be demonstrated
by staining in liver or other tissues. Findings in this in vivo murine model of passive
NH alloimmunity provide evidence of an alloimmune mechanism for NH-related liver injury.
To determine the mechanism of NH-IgG mediated liver necrosis, NH-IgG was applied to
fetal mouse hepatocytes in culture in the presence and absence of bovine complement.
In the absence of complement, hepatocytes showed substantial human IgG bound to their
surface, whereas control IgG did not bind. NH-IgG in presence of complement resulted
in extensive cell necrosis, whereas control IgG did not. These in vitro findings suggest
that NH-alloimmunity involves IgG binding to hepatocytes followed by complement-dependent
cytolysis. Much additional work is needed to confirm these findings and to further
elucidate the mechanisms of injury.
It is not known at present if all NH is alloimmune. It appears that the NH phenotype,
at least early-onset liver failure and hepatic siderosis, can occasionally result
from fetal liver injury due to genetic/metabolic disease and perinatal infection.[13]
[24]
[25] Several groups continue to search for a gene locus whose mutation might cause NH.[19]
[26] Although there is reason to believe that the majority represents a humoral alloimmune
fetal liver injury, a reliable serologic test for NH-associated antibody will be needed
to prove this. It should be possible with such a test to determine if all cases of
NH represent a single disease-alloimmune NH-or if there are some cases that are secondary
to another, perhaps sporadic, fetal liver injury. This might explain the cases where
NH does not recur for some women.
PATHOLOGY
PATHOLOGY
Autopsy specimens from stillbirths and newborns have provided most of the pathologic
descriptions of the disease. The liver injury in NH is very severe and out of proportion
to that seen in other forms of hemochromatosis.[1]
[2] Cirrhosis is evident in nearly all cases. Fibrosis is pronounced, particularly in
the lobule and around the central vein. Regenerative nodules may be present. In some
instances, almost no hepatocytes remain. The residual and/or regenerating hepatocytes
may exhibit either giant cell or pseudoacinar transformation with canalicular bile
plugs. The histopathology often resembles that seen in acute and subacute liver failure
in older individuals (Fig. [1]). Residual hepatocytes often show siderosis while Kupffer cells are spared. The
siderosis is coarsely granular, which is in contrast with the hazy iron staining of
normal newborn liver. Considerable acute and chronic inflammation is usually evident.[27]
Figure 1 Severely damaged liver in a 6-week-old baby with NH who had a liver transplant due
to liver failure. The main image shows several areas of parenchymal collapse and scarring,
with formation of thick fibrous septa and parenchymal regenerative nodules. The inset
shows severely injured hepatocytes, which show marked variation in size and shape,
pseudoacinar transformation, and severe cholestasis. (H&E-stained sections. Original
magnifications: main image, × 100; inset, × 400.)
Siderosis may affect any of several tissues outside the liver.[2]
[3]
[28]
[29] The most consistently affected are the acinar epithelium of the exocrine pancreas,
myocardium, the epithelia of the thyroid follicles, and the mucosal (“minor salivary”)
glands of the oronasopharynx and respiratory tree. Less affected are gastric and Brunner
glands, parathyroid glands, choroid plexus, thymus (Hassall corpuscles), pancreatic
islets, the adenohypophysis, and chondrocytes in hyaline cartilage. The spleen, lymph
nodes, and bone marrow contain comparatively trivial quantities of stainable iron.
Occasionally, severely affected babies exhibit renal hypoplasia, with dysgenesis of
proximal tubules.[30]
[31] Correlation with the process of normal renal development dates this arrest of renal
development to ∼24 weeks gestation. It is believed that this final stage of renal
development is dependent upon liver function, and therefore the disordered development
dates liver failure to the late second and early third trimesters.
SIGNS, SYMPTOMS, AND LABORATORY FINDINGS
SIGNS, SYMPTOMS, AND LABORATORY FINDINGS
NH is nearly always accompanied by severe fetal liver injury, and one of its most
common presentations is late-second and third trimester fetal loss as evidenced by
the gestational histories of women who have had a baby diagnosed with NH. Most affected
live-born babies show evidence of fetal insult (i.e., intrauterine growth restriction
[IUGR] and oligohydramnios), and premature birth is common.[1] Liver disease is generally apparent within hours of birth, and NH is one of the
most commonly recognized causes of liver failure in the neonate.[32]
[33]
[34] In rare cases, the liver disease takes a prolonged course and is manifest days to
weeks after birth.[35] There is a spectrum of disease, and some infants recover with supportive care.[36]
[37] Indeed, it may be that some “affected” babies have no clinical disease. Twins may
have disparate clinical findings, with one severely affected and the other minimally
so.[38]
The presenting findings are those of liver failure and usually multiorgan failure.
Affected babies are frequently diagnosed as having overwhelming sepsis of the newborn
even with negative cultures. Hypoglycemia, marked coagulopathy, hypoalbuminemia and
edema with or without ascites, and oliguria are prominent features. Affected babies
are sometimes said to have “nonimmune hydrops” due to the anasarca they exhibit. Jaundice
develops during the first few days after birth. Most cases exhibit significant elevations
of both conjugated and nonconjugated bilirubin, with total bilirubin levels often
exceeding 30 mg/dL. Serum aminotransferase concentrations are disproportionately low
for the degree of hepatic injury, whereas circulating concentrations of α-fetoprotein
(AFP) are characteristically very high, usually 100,000 to 600,000 ng/mL (normal newborn
values < 80,000 ng/mL).[1]
[21] Elevated concentrations of AFP in NH could be due to failure to downregulate the
synthesis of AFP, which is a normal part of the switch from a fetal to a neonatal
metabolic pattern occurring near the end of pregnancy. We hypothesize that the low
aminotransferase activities reflect a similar failure of the perinatal metabolic switch,
which normally results in turning on gluconeogenic pathways that include the aminotransferases.
Exhaustion of hepatocyte mass might also contribute to the low levels; however, infants
who survive with medical therapy and thus obviously do not have exhausted hepatocyte
mass also have low serum aminotransferase levels. In these babies, recovery is often
heralded by increasing serum aminotransferase levels. Studies of iron status often
show hypersaturation of available transferrin, with hypotransferrinemia and hyperferritinemia
(values > 800 ng/mL), which though characteristic in NH are nonspecific in liver disease
of the newborn infant.[39] The low transferrin levels probably reflect severe liver disease. Notably, patients
may receive the diagnosis of tyrosinemia based on elevated serum tyrosine levels,
which are reflective of failed hepatic metabolic function. However, succinylacetone
is absent in the urine. Also, characteristic of NH is persistent patency of the ductus
venosus, which can be demonstrated by sonography,[1] the cause of which is unclear.
DIAGNOSIS
DIAGNOSIS
NH should be suspected in infants who manifest liver disease antenatally or very shortly
after birth. It should also be suspected in unexplained cases of stillbirth. Demonstration
of extrahepatic siderosis is currently necessary to prove the diagnosis. No other
disease of the newborn demonstrates the combination of severe liver disease and extrahepatic
siderosis, and thus the combination of findings is absolutely diagnostic. Caution
should be exercised in evaluating hepatocyte siderosis for the purpose of diagnosing
NH. Finding siderosis in the liver is not diagnostic. The normal newborn liver contains
sufficient stainable iron to be confused with pathologic siderosis, although they
are qualitatively different to the eyes of experienced pathologists. Furthermore,
pathologic hepatic siderosis has been described in several neonatal liver diseases;
however none in combination with extrahepatic siderosis. The absence of stainable
iron in the liver does not exclude the diagnosis of NH as in many cases few if any
hepatocytes remain, and hepatic siderosis in NH involves hepatocytes exclusively.
NH is often diagnosed at autopsy, where siderosis of many tissues can be demonstrated
if looked for. Proper stains for iron (Prussian blue, Perl's stain) should be performed
on the tissues typically involved (see “Pathology” section above) when autopsy is
performed on any baby with liver failure or suspected liver disease and in unexplained
stillbirths. Failure to do so has resulted in many missed diagnoses with dire consequences
for subsequent pregnancies of affected women. Demonstration of extrahepatic siderosis
in living babies can be by tissue biopsy or by magnetic resonance imaging (MRI) (Fig.
[2]). Biopsy of the oral mucosa is a clinically useful approach to obtain glandular
tissue in which to demonstrate siderosis.[28]
[40] Differences in magnetic susceptibility between iron-laden and normal tissues on
T2-weighted MRI can document siderosis of various tissues, particularly the pancreas
and liver.[41]
[42] The diagnostic utility of these approaches has never been formally evaluated. Oral
mucosal biopsy often fails because an inadequate specimen not containing submucosal
glands is obtained. Experience suggests that adequate biopsies contain some stainable
iron (any amount is abnormal) in more than two thirds of cases with severe liver disease,[40] whereas MRI demonstrates abnormal iron distribution in ∼90% of such cases.
Figure 2 The diagnosis of NH depends on demonstrating iron in extrahepatic tissue. The MRI
(T2-weighted) and the iron-stained section of buccal mucosa from a newborn with NH
are demonstrated. The MRI (left panel) demonstrates attenuated signal (dark) from
the liver and pancreas relative to the spleen, indicating increased iron content.
The buccal biopsy shows iron deposition in epithelium of submucosal glands (black
flecks in glandular epithelium). Both findings are diagnostic of NH in a baby with
evidence of liver disease or liver failure. This baby survived with medical therapy.
A question remains whether NH can be diagnosed in the absence of extrahepatic siderosis
and/or severe liver disease. Our growing experience drawn from sibships suggests that
there is a spectrum of both findings, assuming that severe liver disease in a sibling
of a baby with NH proved by standard criteria is due to NH. We have seen acute liver
failure with confluent hepatic necrosis in a 21-week fetus in which no siderosis could
be demonstrated in liver or other tissues. Conversely, fraternal twins of affected
babies have been minimally affected with no clinical liver disease.[38] Finally, we have seen autopsy materials from fetal products of late intrauterine
demise where autolysis and maceration prevented diagnosis of NH-associate liver disease
and no siderosis was detectable, yet subsequent offspring of the affected women had
NH proven by standard criteria. Better diagnostic tests and/or criteria are needed
before the full spectrum of this disease can be recognized.
Because a fetus in a mother who has borne an infant with NH is at risk, antenatal
diagnosis has been attempted. Fetal sonography can provide indirect evidence of liver
injury, in particular placental or fetal edema, in the third trimester. MRI has not
been useful in identifying hemochromatotic siderosis in utero.
TREATMENT AND OUTCOME
TREATMENT AND OUTCOME
The prognosis in severe NH is generally very poor.[1]
[34]
[43]
[44] The average life expectancy of the average severely affected baby is days to a few
weeks. NH is a frequent indication for liver transplantation in the first 3 months
of life.[32]
[33]
[45]
[46]
[47] When performed for NH, the difficulties attendant to transplanting newborns are
frequently compounded by prematurity, small size for gestational age, and multiorgan
failure. Furthermore, it is clear that babies with clinical liver failure due to NH
can fully recover with medical support.[36]
[37]
[43]
[44] Thus, caution is indicated when considering treating an affected baby with liver
transplantation.
Current medical treatment is less than satisfactory. A cocktail containing both antioxidants
and an iron chelator has been used to treat NH.[1]
[43]
[48] Success rates with medical treatment have been reported to be 10% to 20%, and it
is not clear what factors determine a successful outcome. Within the spectrum of severe
NH, it may be that patients with more hepatic reserve profit from it, whereas more
severely affected patients fail to respond. This therapy was based on the hypothesis
that oxidative injury due to iron overload was central to disease pathogenesis, which
appears not to be the case. Treatment of neonates severely affected with alloimmune
(i.e., thrombocytopenia) and passive autoimmune (i.e., lupus heart block) diseases
is based on one principle: remove the maternal IgG to preclude further immune injury.
A rational approach to treating NH based on its alloimmune causation would be to combine
the cocktail with double volume exchange transfusion (with blood reconstituted from
packed red blood cells and fresh-frozen plasma from unrelated donors) to remove the
maternal alloantibody followed by administration of intravenous immunoglobulin to
restore broad humoral immunity. This approach might be expected to reduce ongoing
immune-mediated injury and perhaps improve function but would not necessarily be effective
in reversing advanced disease including cirrhosis. A limited experience with this
approach suggests that it offers some improvement in outcome.[49]
Limited published experience exists with regard to the outcome of babies who survive
severe NH with medical therapy. Our experience with 6 such babies suggests that full
recovery is likely. All were in clinical liver failure shortly after birth and had
clinical evidence of cirrhosis including a hard liver, ascites, and caput medusa.
All were treated with the antioxidant/chelation cocktail. Four of the 6 experienced
at least 1 episode of sepsis possibly related to the use of desferrioxamine, which
is toxic to neutrophils. Recovery from liver failure to ability to discharge to home
varied from 1 to 4 months. All 6 babies ultimately recovered fully with no residual
clinical liver disease after a period of 1 to 2 years. In a unique experience, 2 of
these babies who are siblings underwent liver biopsy as neonates and again after 2
to 4 years.[50] The initial biopsies demonstrated typical histology of severe NH with a pathologic
diagnosis of cirrhosis. The repeat biopsies demonstrated normal histology with no
pathologic findings. Although a very limited experience, this suggests that the neonatal
liver affected with NH is quite plastic and capable of recovery even from severe injury.
Accumulating experience indicates that recurrence of severe NH can be prevented by
treatment during gestation.[21]
[51] The treatment consists of intravenous immunoglobulin (IVIG) derived from pooled
serum of multiple donors administered weekly at a dose of 1 g/kg body weight from
the 18th week until the end of gestation. This is a modification of the treatment
commonly used to reduce the severity of other gestational alloimmune diseases. Women
whose most recent gestation was affected with proven NH should be treated in lieu
of any other marker for high risk of recurrence. At the time of writing, 46 babies
have been born to mothers receiving gestational treatment. No IUGR, fetal liver disease,
or other evidence of fetal distress has been detected in any case. Few babies born
after gestational treatment have had significant clinical liver disease. However,
biochemical evidence suggests that ∼80% of babies were affected: elevated serum AFP
(range, 100,820 to 670,000 ng/mL) and/or elevated serum ferritin (range, 1250 to 15,948
ng/mL). This growing experience suggests that treatment with high-dose IVIG during
gestation modifies recurrent NH so that it is not lethal to the fetus or the newborn.
CONCLUSION
CONCLUSION
NH is a prominent cause of severe fetal liver injury and should be suspected in cases
of late intrauterine fetal demise in the absence of other definable cause. It should
be suspected in any very sick newborn with evidence of liver disease as it is the
cause of most cases of newborn liver failure and/or cirrhosis. Diagnosis is confirmed
by demonstrating extrahepatic siderosis. However, there is a spectrum of NH-related
phenotypes that can include minimally affected siblings of affected babies and acute
liver failure in the absence of extrahepatic siderosis. NH appears to be the manifestation
of maternal alloimmunity in many cases. The risk for recurrence in subsequent offspring
of an affected woman is very high, though prevention of recurrent severe NH by gestational
treatment using IVIG has been very effective. Thus, it is imperative to diagnose NH
in an affected fetus or baby through proper study including autopsy. Ongoing research
should lead to better approaches to diagnosis and treatment.
ABBREVIATIONS
ABBREVIATIONS
-
AFP α-fetoprotein
-
H&E hematoxylin and eosin
-
HFE hemochromatosis gene
-
IgG immunoglobulin G
-
IUGR intrauterine growth restriction
-
IVIG intravenous immunoglobulin
-
MRI magnetic resonance imaging
-
NH neonatal hemochromatosis
