Inheritable Forms of Liver Disease

Hemochromatosis

• 1.

  How do we classify the various iron-loading disorders in humans?

  The usual way to classify iron-overload syndromes is to distinguish between hereditary hemochromatosis (HH), secondary iron overload, and parenteral iron overload.

  • HH results in increased iron absorption from the gut, with preferential deposition of iron in the parenchymal cells of the liver, heart, pancreas, and other endocrine glands. Most HH (approximately 85% to 90%) is found in patients who are homozygous for the C282Y mutation found in HFE, the gene for hemochromatosis. Over the past several years, however, mutations in other genes have been found that can lead to iron overload. These include mutations in transferrin receptor-2 (TfR2), ferroportin, hemojuvelin, and hepcidin.

  • In secondary iron overload, some other stimulus causes the gastrointestinal tract to absorb increased amounts of iron. Here, the increased absorption of iron is caused by an underlying disorder rather than by an inherited defect in regulation of iron absorption. Examples include various anemias caused by ineffective erythropoiesis (e.g., thalassemia, aplastic anemia, red cell aplasia, and some patients with sickle cell anemia), chronic liver disease, and, rarely, excessive intake of medicinal iron.

  • In parenteral iron overload, patients have received excessive amounts of iron as either red blood cell transfusions or iron-dextran given parenterally. In patients with severe hypoplastic anemias, red blood cell transfusion may be necessary. Over time, patients become significantly iron loaded. Unfortunately, some physicians give iron-dextran injections to patients with anemia that is not due to iron deficiency; such patients can become iron loaded. Parenteral iron overload is always iatrogenic and should be avoided or minimized. In patients who truly need repeated red blood cell transfusions (in the absence of blood loss), a chelation program with deferoxamine should be initiated to prevent toxic accumulation of excessive iron.

• 2.

  What are neonatal iron overload and African iron overload?

  • Neonatal iron overload is a rare condition that is probably related to an immune-mediated intrauterine hepatic defect. Infants are born with modest increases in hepatic iron and many patients do very poorly; liver transplantation can be lifesaving.

  • African iron overload, previously called Bantu hemosiderosis, was thought to be a disorder in which excessive amounts of iron were ingested from alcoholic beverages brewed in iron drums. Recent studies have suggested that this disorder does have a genetic component and some patients have mutations in ferroportin. Thus black patients may be at risk for developing iron overload from an inherited disease.

• 3.

  How much iron is usually absorbed per day?

  A typical Western diet contains approximately 10 to 20 mg of iron, which usually is found in heme-containing compounds. Normal daily iron absorption is approximately 1 to 2 mg, representing approximately a 10% efficiency of absorption. Patients with iron deficiency, HH, or ineffective erythropoiesis absorb increased amounts of iron (up to 3 to 6 mg/day).

• 4.

  Where is iron normally found in the body?

  The normal adult male contains approximately 4 g of total body iron, which is roughly divided between the 2.5 g of iron in the hemoglobin of circulating red blood cells, 1 g of iron in storage sites in the reticuloendothelial system of the spleen and bone marrow and the parenchymal and reticuloendothelial system of the liver, and 200 to 400 mg in the myoglobin of skeletal muscle.

  In addition, all cells contain some iron because mitochondria contain iron both in heme, which is the central portion of cytochromes involved in electron transport, and in iron sulfur clusters, which also are involved in electron transport. Iron is bound to transferrin in both the intravascular and extravascular compartments. Storage iron within cells is found in ferritin and, as this amount increases, in hemosiderin. Serum ferritin is proportional to total body iron stores in patients with iron deficiency or uncomplicated HH and is biochemically different from tissue ferritin.

• 5.

  Discuss the genetic defect in patients with HH.

  In 1996, the gene responsible for hemochromatosis was identified and named HFE . HFE codes for a major histocompatibility complex (MHC) type 1–like protein that is membrane spanning with a short intracytoplasmic tail, a transmembrane region, and three extracellular alpha loops. A single missense mutation results in loss of a cysteine at amino acid position 282 with replacement by a tyrosine (C282Y), which leads to disruption of a disulfide bridge and thus to the lack of a critical fold in the alpha ₁ loop. As a result, HFE fails to interact with β ₂ -microglobulin (β ₂ M), which is necessary to the function of MHC class 1 proteins.

  In 1997, it was demonstrated that the HFE /β ₂ M complex binds to transferrin receptor and is necessary for transferrin receptor–mediated iron uptake into cells. This observation linked HFE with a protein of iron metabolism. C282Y homozygosity is found in approximately 85% to 90% of patients with hemochromatosis. A second mutation, whereby a histidine at amino acid position 63 is replaced by an aspartate (H63D), is common but less important in cellular iron homeostasis. A third mutation has been characterized whereby a serine is replaced by a cysteine at amino acid position 65 (S65C). Like H63D, S65C has little effect on iron loading unless it is present as a compound heterozygote with the C282Y mutation. Additional discoveries show that hepcidin, a 25–amino acid peptide, is found to be deficient in patients with hemochromatosis and is considered the iron regulatory hormone. Thus in patients with HFE mutations and in those with mutations in TfR2, hemojuvelin, and hepcidin, there is a deficiency of hepcidin production by the liver. Hepcidin in normal amounts interferes with the activity of ferroportin at the basolateral surface of the enterocyte, preventing iron absorption. Thus when there is hepcidin deficiency, there is an increase in iron absorption despite the fact that individuals are in fact iron loaded.

• 6.

  What are the usual toxic manifestations of iron overload?

  In chronic iron overload, an increase in oxidant stress results in lipid peroxidation to lipid-containing components of the cell, such as organelle membranes. This process causes organelle damage. Hepatocellular injury or death ensues with phagocytosis by Kupffer cells. Iron-loaded Kupffer cells become activated, producing profibrogenic cytokines such as transforming growth factor β ₁ , which, in turn, activates hepatic stellate cells. Hepatic stellate cells are responsible for increased collagen synthesis and hepatic fibrogenesis.

• 7.

  What are the most common symptoms in patients with HH?

  Currently, most patients are identified by abnormal iron studies on routine screening chemistry panels or by screening family members of a known patient. When identified in this manner, patients typically have no symptoms or physical findings. Nonetheless, it is useful to be aware of the symptoms that patients with more established HH can exhibit. Typically, they are nonspecific and include fatigue, malaise, and lethargy. Other more organ-specific symptoms are arthralgias and symptoms related to complications of chronic liver disease, diabetes, and congestive heart failure.

• 8.

  Describe the most common physical findings in patients with HH.

  The way in which patients come to medical attention determines whether they have physical findings. Currently, most patients at diagnosis have no symptoms and no findings. Thus patients identified by screening tests have no abnormal physical findings. In contrast, physical findings in patients with advanced disease may include grayish or “bronzed” skin pigmentation, typically in sun-exposed areas; hepatomegaly with or without cirrhosis; arthropathy with swelling and tenderness over the second and third metacarpophalangeal joints; and other findings related to complications of chronic liver disease.

• 9.

  How is the diagnosis of hemochromatosis established?

  Patients with abnormal iron studies on screening blood work, any of the symptoms and physical findings of hemochromatosis, or a positive family history of hemochromatosis should have blood studies of iron metabolism either repeated or performed for the first time. These studies include serum iron, total iron-binding capacity (TIBC) or transferrin, and serum ferritin. The transferrin saturation (TS) should be calculated from the ratio of iron to TIBC or transferrin. If the TS is greater than 45% or if the serum ferritin is elevated, hemochromatosis should be strongly considered, especially in patients without evidence of other liver disease (e.g., chronic viral hepatitis, alcoholic liver disease, nonalcoholic steatohepatitis) known to have abnormal iron studies in the absence of significant iron overload.

  If iron studies are abnormal, mutation analysis of HFE should be performed. If patients are homozygous for the C282Y mutation or compound heterozygotes (C282Y/H63D) and younger than the age of 40 years or in those with normal liver enzymes (alanine aminotransferase and aspartate aminotransferase) and a ferritin level less than 1000 ng/mL, no further evaluation is necessary. Plans for therapeutic phlebotomy can be initiated. In patients older than the age of 40 years or with abnormal liver enzymes or markedly elevated ferritin (greater than 1000 ng/mL), the next step is to perform a percutaneous liver biopsy to obtain tissue for routine histologic examination, including Perls’ Prussian blue staining for storage iron and biochemical determination of hepatic iron concentration (HIC). The main purpose for performing a liver biopsy in these individuals is to determine the degree of fibrosis because increased fibrosis has been associated with markedly elevated ferritin levels and elevated liver enzymes. Also, biochemical determination of HIC can be obtained and then from the HIC, the hepatic iron index (HII) can be calculated. Calculation of the HII was more important in the past than it is now because we have genetic testing.

• 10.

  Are there genetic tests available for determining non–HFE-linked causes of HH?

  Yes. Diagnostic DNA laboratories have developed assays for hemojuvelin, hepcidin, ferroportin, and transferrin-receptor-2 in addition to HFE mutation analysis.

• 11.

  How commonly do abnormal iron studies occur in other types of liver diseases?

  In various studies, approximately 30% to 50% of patients with chronic viral hepatitis, alcoholic liver disease, and nonalcoholic steatohepatitis have abnormal serum iron studies. Abnormalities in serum iron studies in the absence of HH are more commonly seen in hepatocellular than cholestatic liver diseases. Usually, the serum ferritin is abnormal. In general, an elevation in TS is much more specific for HH. Thus if the serum ferritin is elevated and the TS is normal, another form of liver disease may be responsible. In contrast, if the serum ferritin is normal and the TS is elevated, the likely diagnosis is hemochromatosis, particularly in young patients. Differentiation of HH in the presence of other liver diseases is now much easier with the use of genetic testing ( HFE mutation analysis for C282Y and H63D).

• 12.

  Is computed tomography (CT) or magnetic resonance imaging (MRI) useful in diagnosing hemochromatosis?

  In massively iron-loaded patients, CT and MRI show the liver to be white or black, respectively, consistent with the kinds of changes associated with increased iron deposition. In more subtle and earlier cases, overlap is tremendous, and imaging studies are not useful. Thus in heavily iron-loaded patients, the diagnosis is usually apparent without imaging tests, and in mild or subtler cases, they are unhelpful. CT or MRI is useful only in the patient who is likely to have moderate to severe iron overload but for whom a liver biopsy is either unsafe or refused. Again, this problem is less common with the advent of genetic testing.

• 13.

  On liver biopsy, what is the typical cellular and lobular distribution of iron in HH?

  In early HH in young people, iron is found entirely in hepatocytes in a periportal (zone 1) distribution. In heavier iron loading in older patients, iron is still predominantly hepatocellular, but some iron may be found in Kupffer cells and bile ductular cells. The periportal-to-pericentral (zone 1–zone 3) gradient is maintained but may be less distinct in more heavily loaded patients. When patients develop cirrhosis, the pattern is typically micronodular, and regenerative nodules may show less intense iron staining.

• 14.

  How useful is HIC?

  Since genetic testing has become readily available, liver biopsy and determinations of HIC and HII are less important. Nonetheless, whenever a liver biopsy is performed in a patient with suspected HH, the quantitative HIC should be obtained. In symptomatic patients, HIC is typically greater than 10,000 mcg/g. The iron concentration threshold for the development of fibrosis is approximately 22,000 mcg/g. Lower iron concentrations can be found in cirrhotic HH with a coexistent toxin, such as alcohol or hepatitis C or B virus. Young people with early HH may have only moderate increases in HIC. In the past, discrepancies in HIC concentration with age were clarified by use of the HII.

• 15.

  How is the HII used in diagnosing HH?

  The HII, introduced in 1986, is based on the observation that HIC increases progressively with age in patients with homozygous HH. In contrast, in patients with secondary iron overload or in heterozygotes, there is no progressive increase in iron over time. Therefore the HII was thought to distinguish patients with homozygous HH from patients with secondary iron overload and heterozygotes. The HII is calculated by dividing the HIC (in μmol/g) by the patient’s age (in years). A value greater than 1.9 was thought to be consistent with homozygous HH. With the advent of genetic testing, we have learned that many C282Y homozygotes do not have phenotypic expression to the degree that would cause an elevated HII and they will not have increased iron stores. Thus the HII is no longer the gold standard for the diagnosis of HH. The HII is not useful in patients with parenteral iron overload.

• 16.

  How do you treat a patient with HH?

  Treatment of HH is relatively straightforward and includes weekly or twice-weekly phlebotomy of 1 unit of whole blood. Each unit of blood contains approximately 200 to 250 mg of iron, depending on the hemoglobin. Therefore a patient who presents with symptomatic HH and who has up to 20 g of excessive storage iron requires removal of more than 80 units of blood, which takes close to 2 years at a rate of 1 unit of blood per week. Patients need to be aware that this treatment can be tedious and prolonged. Some patients cannot tolerate removal of 1 unit of blood per week, and occasionally schedules are adjusted to remove only $\frac{1}{2}$ unit every other week. In contrast, in young patients who are only mildly iron-loaded, iron stores may be depleted quickly with only 10 to 20 phlebotomies. The goal of initial phlebotomy treatment is to reduce tissue iron stores, not to create iron deficiency. Once the ferritin is less than 50 ng/mL and the TS is less than 50%, the majority of excessive iron stores has been successfully depleted, and most patients can go into a maintenance phlebotomy regimen (1 unit of blood removed every 2 to 3 months).

• 17.

  What kind of a response to treatment can you expect?

  Many patients feel better after phlebotomy therapy has begun, even if they were asymptomatic before treatment. Energy level may improve, with less fatigue and less abdominal pain. Liver enzymes typically improve once iron stores have been depleted. Increased hepatic size diminishes. Cardiac function may improve, and approximately 50% of patients with glucose intolerance are more easily managed. Unfortunately, advanced cirrhosis, arthropathy, and hypogonadism do not improve with phlebotomy.

• 18.

  What is the prognosis for a patient with hemochromatosis?

  Patients who are diagnosed and treated before the development of cirrhosis can expect a normal life span. The most common causes of death in hemochromatosis are complications of chronic liver disease and hepatocellular cancer. Patients who are diagnosed and treated early should not experience any of these complications.

• 19.

  Because hemochromatosis is an inherited disorder, what is the practitioner’s responsibility to family members once a patient has been identified?

  Once a patient has been fully identified, all first-degree relatives should be offered screening with genetic testing ( HFE mutation analysis for C282Y and H63D) and tests for TS and ferritin. If genetic testing shows that the relative is a C282Y homozygote or a compound heterozygote (C282Y/H63D) and has abnormal iron studies, HH is confirmed. A liver biopsy may not be necessary. Human leukocyte antigen studies are no longer performed.

• 20.

  Should general population screening be done to evaluate for hemochromatosis?

  With the advent of genetic testing, it was suggested that HH may be a good disease for population screening. This was because genetic testing was available, phenotypic expression was easy to determine, there was a long latent period between diagnosis and disease manifestations, and treatment is effective and safe. Several large-scale population studies have been performed and demonstrate that approximately half of C282Y homozygotes have evidence of phenotypic expression with increased iron stores. Thus interest in population screening has waned because many people would be identified with a genetic disorder who do not go on to develop iron overload.