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A 45-year-old man presented with jaundice, abdominal swelling due to ascites, and elevated liver function tests. He reported 1 – 2 alcoholic drinks per week and had a thin body habitus. Family history was negative for liver disease. Following diagnostic liver biopsy, he was listed for orthotopic liver transplant. A section of his explanted native liver is provided.
Archive Case and Diagnosis:
This case first appeared as Performance Improvement Program in Surgical Pathology (PIP) 2009, case 25, and is alpha-1-antitrypsin deficiency.
Criteria for Diagnosis and Comments:
The explanted liver shows features typical of alpha-1-antitrypsin (AAT) deficiency. There is a pattern of micronodular cirrhosis with expansile as well as bridging fibrosis of portal tracts. Some hepatocytes show characteristic large cytoplasmic globules visible on H&E stain, which were also highlighted by Periodic acid Schiff stain and immunohistochemistry for AAT.
AAT deficiency is the most common genetic cause of liver disease in children and a major cause of hereditary liver dysfunction in adults, second only to hereditary hemochromatosis as the leading genetic cause of liver disease in adults. AAT is a glycoprotein produced predominantly in hepatocytes that functions as an inhibitor of serine proteases. AAT deficiency is caused by mutations in the SERPINA1 gene on chromosome 14q31-32.3 and is inherited in an autosomal recessive pattern. The genetic mutation results in a conformational abnormality (misfolding) of the AAT glycoprotein, abnormal retention of a polymerized form in the endoplasmic reticulum of hepatocytes, and low serum levels of AAT (approximately 15% normal). The normal allele is designated PiM and the two most common variant alleles are PiS and PiZ, resulting from single base pair mutations in exons III and V, respectively. The resultant amino acid substitutions in the AAT protein alter the net charge of the protein and allow detection of the normal type (MM), carrier types (MS, MZ) and deficiency variants (SS, SZ, ZZ) by isoelectric focusing (Pi (protease inhibitor) typing). Hepatic cirrhosis is most often associated with PiZZ type.
AAT deficiency has an incidence of approximately 1 in 4000 livebirths, with 3.4 million AAT-deficient individuals and 116 million carriers worldwide. Although generally considered to be a disease of Caucasians from northern Europe, AAT deficiency is known to occur in all racial groups and is underdiagnosed, particularly in non-Caucasian populations. AAT deficiency results in severe liver disease in only approximately 3 – 10% of affected individuals, suggesting a role for other modifier genes and concurrent environmental factors potentiating the progression of liver disease. Age at presentation is highly variable, from the neonatal period to adulthood. Signs and symptoms of liver disease in infancy include neonatal cholestasis, conjugated hyperbilirubinemia, abdominal swelling, and poor feeding, whereas the more slowly progressive forms manifesting in late childhood or adulthood typically produce fatigue, poor appetite, abdominal swelling, asymptomatic hepatomegaly and/or splenomegaly, jaundice, pruritis, peripheral edema, and abnormal elevation of liver enzymes.
The pathologic consequences of deficient alpha-1-antitrypsin are primarily restricted to the lungs and liver. In the lung, deficiency of serum alpha-1-antitrypsin results in unopposed proteolytic destruction of alveolar tissue by neutrophil elastase, and therefore results in progressive panacinar emphysema, typically presenting in the fifth or sixth decade of life in non-smokers and fourth decade of life in smokers. Other pulmonary manifestations include chronic bronchitis, bronchiectasis, and asthma. In the liver, endoplasmic reticulum storage of the abnormal protein results in progressive liver injury, hepatitis, liver failure, and cirrhosis. The pathogenesis of liver cell injury is thought to be secondary to mitochondrial injury, activation of autophagy, and caspase activation leading to apoptosis. Hepatocellular carcinoma is also an associated complication. Other reported systemic diseases associated with AAT deficiency include necrotizing panniculitis, glomerulonephritis, arterial aneurysms, gastrointestinal bleeding, rheumatoid arthritis, anti-proteinase3-associated vasculitis (Wegener granulomatosis), and other immune-mediated vasculitis.
Although not required for diagnosis in most cases, liver biopsy is often performed for confirmation of diagnosis, evaluation of disease progression and fibrosis, and assessment of co-morbid states. Histopathologic manifestations of AAT deficiency in the liver vary according to age at biopsy. In early infancy, the diagnosis may be challenging due to variation in histologic patterns and inconspicuous nature of cytoplasmic AAT globules. The three typical histologic patterns in early infancy include: (1) hepatocellular necrosis, (2) bile duct proliferation, and (3) bile duct paucity. The hepatocellular necrosis pattern is characterized by canalicular cholestasis, hepatocyte necrosis and ballooning, and giant cell transformation. The bile duct proliferation pattern is characterized by canalicular cholestasis, bile duct proliferation, and hepatocyte injury. The bile duct paucity pattern occurs in approximately 10% of neonates with AAT deficiency and resembles Alagille syndrome due to reduced bile duct to portal tract ratio. By late infancy, portal fibrosis may be evident, in some cases associated with bridging fibrosis or cirrhosis. Inflammatory infiltrates or hepatocyte necrosis are typically inconspicuous. In adults, the histologic manifestations of AAT deficiency may include portal inflammation and piecemeal necrosis (chronic active hepatitis), lobular hepatitis, steatosis, portal fibrosis, or cirrhosis.
The most important diagnostic feature associated with AAT deficiency is the presence of large eosinophilic cytoplasmic globules, recognizable on H&E stained sections and best highlighted by Periodic acid Schiff stain and/or immunohistochemistry for alpha-1-antitrypsin. Ultrastructural examination of these hepatocytes confirms amorphous finely granular proteinaceous material within dilated endoplasmic reticulum, often forming large pools surrounded by an electron-lucent halo. The PAS-positive diastase-resistant globules tend to be most prominent in periportal hepatocytes and are more conspicuous in older children and adults than in neonates, in whom they may be absent. It should be noted that similar globules of AAT have been associated with other liver diseases as an acute phase reactant, and correlation with serum AAT level is helpful in distinguishing AAT deficiency in such cases.
In neonates, the differential diagnosis of AAT deficiency is dependent on the histologic pattern, but includes extrahepatic biliary atresia (duct proliferation pattern), neonatal giant cell (viral) hepatitis (hepatocellular necrosis pattern), and Alagille syndrome (bile duct paucity pattern). In adults, the differential diagnosis of chronic hepatitis and cirrhosis is broad and includes alcoholic cirrhosis, hepatitis B or C viral infection, non-alcoholic fatty liver disease, autoimmune hepatitis, Wilson’s disease, and hereditary hemochromatosis. All of these are distinguished by clinical features, viral PCR and serologic studies, autoimmune serology, and special stains for iron and copper. The presence of low serum AAT and distinctive PAS-positive globules in liver tissue help to distinguish AAT deficiency from these entities. Other types of endoplasmic reticulum storage disease should also be considered in the differential diagnosis, such as alpha-1-antichymotrypsin deficiency, hereditary hypofibrinogenemia, and anti-thrombin III deficiency. Like AAT deficiency, these entities have hepatocellular cytoplasmic inclusions and dilated endoplasmic reticulum, although immunohistochemistry for AAT is negative. The protein material within the endoplasmic reticulum in alpha-1-antichymotrypsin deficiency appears amorphous and “fluffy,” whereas the protein material in hypofibrinogenemia forms curved tubular structures in a fingerprint-like pattern. Also, the inclusions associated with hypofibrinogenemia may appear more like Lafora bodies or ground-glass inclusions as in hepatitis B infection, rather than the more distinct globules of AAT deficiency. Correlation with clinical features and serum levels of each of these proteins also helps to distinguish these rare disorders.
Current therapy for AAT deficiency includes supportive care with enzyme replacement by intravenous infusion of pooled AAT to prevent progression of pulmonary emphysema. AAT replacement is ineffective for prevention of liver injury or cirrhosis, and liver transplantation is the only available therapeutic option for severe or end-stage liver disease.