Conceptual advances in the pathogenesis and treatment of childhood metabolic liver disease

Gene therapy for inherited diseases of liver metabolism

Gene therapy is entering the stage of initial clinical development to treat a growing number of inherited metabolic diseases. This review outlines the development of liver-directed gene therapy for diseases caused by deficiencies of enzymes that are primarily expressed in the liver and discusses the disorders that appear most promising for clinical translation.

Therapeutic targeting of misfolding and conformational change in α1-antitrypsin deficiency

Misfolding and conformational diseases are increasing in prominence and prevalence. Both misfolding and ‘postfolding’ conformational mechanisms can contribute to pathogenesis and can coexist. The different contexts of folding and native state behavior may have implications for the development of therapeutic strategies. α1-antitrypsin deficiency illustrates how these issues can be addressed with therapeutic approaches to rescue folding, ameliorate downstream consequences of aberrant polymerization and/or maintain physiological function. Small-molecule strategies have successfully targeted structural features of the native conformer. Recent developments include the capability to follow solution behavior of α1-antitrypsin in the context of disease mutations and interactions with drug-like compounds. Moreover, preclinical studies in cells and organisms support the potential of manipulating cellular response repertoires to process misfolded and polymer states.

Gene therapy for inborn errors of liver metabolism: progress towards clinical applications

The treatment for inborn errors of liver metabolism is based on dietary, drug, and cell therapies (orthotopic liver transplantation). However, significant morbidity and mortality still remain, and alternative strategies are needed. Gene replacement therapy has the potential of providing a definitive cure for patients with these diseases. Significant progress has been made in the pre-clinical arena and achievement of efficacy in different animal models has been reported using multiple gene transfer technologies. This article summarizes the gene transfer strategies being investigated, the pre-clinical data, and the available early clinical results for inborn errors of liver metabolism.

Miglustat

Miglustat is an orally administered ceramide glucosyltransferase inhibitor which prevents the lysosomal accumulation of glucocerebroside that occurs in patients with Gaucher's disease. In noncomparative trials in patients with type 1 Gaucher's disease, miglustat (50 or 100mg three times daily) for 6-12 months significantly reduced baseline liver and spleen volumes. At both 6 and 12 months, the reductions in organ volumes were greater with the higher dosage. Miglustat 50 or 100mg three times daily for 6-12 months had no significant effect on haemoglobin concentrations. Baseline platelet counts were not significantly improved by either dosage at 6 months, although the higher dosage significantly increased platelet counts at 12 months. In an open extension phase, patients continued to show further reductions in organ volume as well as significant improvements in haematological parameters at 24 and 36 months. black triangle In a 6-month randomised study in patients with type 1 Gaucher's disease who had previously received long-term enzyme replacement therapy (ERT), liver volume reduction was greater with miglustat plus ERT than with ERT alone. Diarrhoea and weight loss were the most frequent adverse events associated with miglustat therapy. Fine tremor has been reported in approximately 30% of miglustat-treated patients.

Alpha1-antitrypsin deficiency-associated liver disease progresses slowly in some children

BACKGROUND

A prospective nationwide screening study initiated more than 20 years ago in Sweden has shown that clinically significant liver disease develops in only 10% to 15% of alpha1-antitrypsin (AT)-deficient children. This study provides information about 85% to 90% of those children, many of whom had elevated serum transaminases in infancy but have no evidence of liver injury by age 18 years. However, there is relatively limited information about the course of alpha1-AT-deficient children who have cirrhosis or portal hypertension. Based on several anecdotal experiences, we have been impressed by the relatively slow progression and stable course of the liver disease in some of these children.

METHODS

We reviewed the course of patients with homozygous PIZZ alpha1-antitrypsin deficiency seen at this institution since establishing a patient database 16 years ago.

RESULTS

Of 44 patients with alpha1-AT deficiency, 17 had cirrhosis, portal hypertension, or both. Nine of the 17 patients with cirrhosis or portal hypertension had a prolonged, relatively uneventful course for at least 4 years after the diagnosis of cirrhosis or portal hypertension. Two of these patients eventually underwent liver transplantation, but seven are leading relatively healthy lives for up to 23 years while carrying a diagnosis of severe alpha1-AT deficiency-associated liver disease. Patients with the prolonged stable course could be distinguished from those with a rapidly progressive course on the basis of overall life functioning but not on the basis of any other more conventional clinical or biochemical criteria.

CONCLUSIONS

These data provide further evidence for the variable severity of liver disease associated with alpha1-AT deficiency and indicate that some patients have chronic, slowly progressing or nonprogressing cirrhosis.

Alpha 1-antitrypsin deficiency

Alpha 1-Antitrypsin deficiency (PiZ) is frequent in Caucasian populations. The predominant clinical correlates of this inborn error, i.e. chronic liver disease, emphysema, and vasculitic syndromes including their pathogenetic background are discussed in the present review.

Liver disease associated with alpha1-antitrypsin deficiency

Alpha1-ATD is the most common metabolic liver disease in children for which liver transplantation is performed and, in adults, is associated with cirrhosis, hepatocellular carcinoma, and emphysema. It appears that only a proportion of patients with the deficiency develop clinical manifestations of this disease. Moreover, recent characterization of specific cellular and physiologic events have provided the basis for future potential therapeutic interventions.

Liver transplantation for hemochromatosis, Wilson's disease, and other metabolic disorders

Liver transplantation provides an effective means for replacing a failing liver, in addition to correcting the underlying abnormality in many metabolic disorders. Results of liver transplantation for metabolic diseases have been generally encouraging, with the exception of hereditary hemochromatosis, in which infectious and cardiac complications appear to increase post-transplant mortality. Better pretransplant diagnosis of hemochromatosis, utilizing the recently identified putative gene, may help reduce post-transplant complications. In metabolic diseases, improved understanding of the underlying genetic and molecular defects will lead to advances in medical therapy and perhaps a decreased need for liver transplantation. NTBC therapy for hereditary tyrosinemia and purified glucocerebroside therapy for Gaucher disease are two such examples. The prospects of gene therapy are being actively pursued for many metabolic diseases, such as CF, hemophilia, and familial hypercholesterolemia. Until such investigation leads directly to clinical practice, however, liver transplantation remains an effective option for therapy for a wide range of metabolic diseases.

Serine protease inhibitors in patients with chronic viral hepatitis

BACKGROUND/AIMS

This study aimed to determine whether deficiency of the major serine protease inhibitors (alpha1-antitrypsin (AAT) or alpha1-antichymotrypsin (ACT)) is associated with increased risk for chronic hepatitis B or C virus (HBV or HCV) infection.

METHODS

We studied 709 adults with chronic liver disease who had undergone liver biopsy during the 14-year period 1978-92. Anti-HCV testing was carried out with second-generation ELISA and immunoblot assays (RIBA 2). HBV markers were tested with commercially available radioimmunoassays. ACT and AAT concentrations in plasma were measured with electroimmunoassay and immune nephelometry. Plasma samples were screened for the AAT PiZ deficiency with ELISA technique and phenotyped by isoelectric focusing. The 229Pro-->Ala mutation for ACT deficiency was identified by PCR techniques.

RESULTS

Of the 709 patients, 132 (18.6%) were positive for anti-HCV according to RIBA 2. PiZ AAT deficiency was found in 44 (6.2%) of patients (one PiZZ, 38 PiMZ, and PiSZ), while subnormal ACT levels were found in 33 (4.6%) patients, frequencies that were higher than expected in the general population (p=0.0375 and p<0.0001, respectively). Of the PiZ-carriers, 8/44 (18%) were found to be anti-HCV positive according to RIBA 2, as compared to 123/662 (19%) non-PiZ-carriers (p>0.05). One of these patients had cirrhosis, four chronic active hepatitis, and three chronic persistent hepatitis. In contrast, 17/33 (51.5%) of the patients with subnormal ACT were anti-HCV positive (OR=5.2, CI=2.6-10.6; p<0.0001). No relationship was found between HBV infection and AAT deficiency or subnormal ACT levels. Only one patient with subnormal ACT levels was heterozygous for the 229Pro-->Ala mutation of ACT deficiency. There was no significant difference in the histological findings when the patients with subnormal ACT levels or PiZ allele were subgrouped according to HCV status.

CONCLUSIONS

There is no overrepresentation of chronic HBV or HCV in heterozygous AAT deficiency, although an association with more severe liver disease in such patients cannot be excluded. In contrast, low plasma levels of ACT that may be acquired or hereditary, due to mutations other than 229Pro-->Ala, are frequent in HCV infection.

Review: alpha 1-antitrypsin deficiency associated liver disease

alpha 1-Antitrypsin (alpha 1-AT) deficiency is the most common genetic cause of liver disease in children and genetic disease for which children undergo liver transplantation. It also causes cirrhosis and hepatocellular carcinoma in adults. Studies by Sveger in Sweden have shown that only a subgroup of the population with homozygous PiZZ alpha 1-AT deficiency develop clinically significant liver injury. Other studies have shown that the mutant alpha 1-AT Z molecule undergoes polymerization in the endoplasmic reticulum and that a subpopulation of alpha 1-AT-deficient individuals may be susceptible to liver injury because they also have a trait that reduces the efficiency by which the mutant alpha 1-AT Z molecule is degraded in the endoplasmic reticulum.

Alpha-1-antitrypsin deficiency: biochemistry and clinical manifestations

Alpha-1-antitrypsin (alpha 1-AT) deficiency is a well known cause of emphysema in adults. A subgroup of deficient individuals develops liver injury during infancy and childhood. In fact, it is the most common genetic cause of liver disease in children. Although lung injury is due to the decrease in alpha 1-AT function in the lung, allowing uninhibited elastolytic destruction of its connective tissue integrity, liver injury is probably due to retention of the mutant alpha 1-AT molecule in the endoplasmic reticulum (ER) of liver cells. Recent studies have shown that the mutant alpha 1-AT molecule polymerizes in the ER by a novel loop-sheet insertion mechanism. Other recent studies show that the subgroup of deficient individuals is susceptible to liver injury by virtue of unlinked genetic traits and/or environmental factors which interfere with degradation of the mutant alpha 1-AT molecules within the ER.

Recent pulmonary observations in alpha 1-antitrypsin deficiency, primary biliary cirrhosis, chronic hepatitis C, and other hepatic problems

Patients with metabolic, immunologic, viral, and other types of hepatic disorders can have a spectrum of complicating pulmonary abnormalities. The natural history of these associations is poorly understood. Significant reversibility in hepatic and pulmonary dysfunction, however, has been well documented in the era of organ transplantation. The continued relationship among pulmonologists, hepatologists, and transplant surgeons hopefully will provide enlightening data on these interesting clinical associations, their natural histories, and their response to evolving therapeutic approaches.