Hereditary tyrosinemia type I (chronic form): pathologic findings in the liver

Liver Transplantation for Pediatric Hepatocellular Carcinoma: A Systematic Review

Simple Summary

Hepatocellular carcinoma is a type of primary liver cancer and the second most common type of liver cancer in children. Although partial hepatectomy can be curative, many children present with tumors that are not amenable to resection and thus the only potentially curative option is liver transplantation. In this systematic review, we have pooled the data from the worldwide literature and showed that survival after liver transplantation for pediatric hepatocellular carcinoma is favorable and many children do well even if their tumors exceed certain potentially restrictive criteria originally developed to select adults with hepatocellular carcinoma for liver transplantation.

Abstract

Liver transplantation (LT) is the only potentially curative option for children with unresectable hepatocellular carcinoma (HCC). We performed a systematic review of the MEDLINE, Scopus, Cochrane Library, and Web of Science databases (end-of-search date: 31 July 2020). Our outcomes were overall survival (OS) and disease-free survival (DFS). We evaluated the effect of clinically relevant variables on outcomes using the Kaplan–Meier method and log-rank test. Sixty-seven studies reporting on 245 children undergoing LT for HCC were included. DFS data were available for 150 patients and the 1-, 3-, and 5-year DFS rates were 92.3%, 89.1%, and 84.5%, respectively. Sixty of the two hundred and thirty-eight patients (25.2%) died over a mean follow up of 46.8 ± 47.4 months. OS data were available for 222 patients and the 1-, 3-, and 5-year OS rates were 87.9%, 78.8%, and 74.3%, respectively. Although no difference was observed between children transplanted within vs. beyond Milan criteria (p = 0.15), superior OS was observed in children transplanted within vs. beyond UCSF criteria (p = 0.02). LT can yield favorable outcomes for pediatric HCC beyond Milan but not beyond UCSF criteria. Further research is required to determine appropriate LT selection criteria for pediatric HCC.

Liver Disease and Risk of Hepatocellular Carcinoma in Children With Mutations in TALDO1

Mutations in the transaldolase 1 (TALDO1) gene have been described in a limited number of cases. Several organs can be affected and clinical manifestations are variable, but often include liver dysfunction and/or hepatosplenomegaly. We report 4 patients presenting with liver disease: 2 with early-onset hepatocellular carcinoma (HCC). Patients with cholestasis and mutations in TALDO1 were identified by next-generation sequencing. Clinical, laboratory, and histological data were collected. Four (1 male) patients were identified with variants predicted to be damaging in TALDO1. Three patients were homozygous (two protein truncating/one missense mutations), 1 one was compound heterozygous (two missense mutations). Median age at presentation was 4 months (range, 2-210 days) with jaundice (3), hepatosplenomegaly (3), and pancytopaenia (1). The diagnosis was corroborated by detection of minimal transaldolase enzyme activity in skin fibroblasts in two cases and raised urine polyols in the third. Three patients underwent liver transplantation (LT), 2 of whom had confirmed HCC on explanted liver. One patient suddenly died shortly after LT. The nontransplanted case has a chronic liver disease with multiple dysplastic liver nodules, but normal liver biochemistry and alpha-fetoprotein. Median follow-up was 4 years (range, 1-21). Conclusion: Transaldolase deficiency can include early-onset normal gamma-glutamyltransferase liver disease with multisystem involvement and variable progression. Patients with this disease are at risk of early-onset HCC and may require early LT.

Case of hepatocellular carcinoma in a patient with hereditary tyrosinemia in the post-newborn screening era

Hereditary tyrosinemia type 1 (HT-1) is a metabolic disorder caused by a defect in tyrosine degradation. Without treatment, symptoms of hepatomegaly, renal tubular dysfunction, growth failure, neurologic crises resembling porphyrias, rickets and possible hepatocellular carcinoma can develop. The use of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione and early diagnosis through newborn screening initiatives have resulted in a sharp decline in morbidity and mortality associated with this disease. We present a case report of a 7-year-old patient with HT-1 who was born prior to the addition of tyrosinemia to the newborn screening in her birth area. At her time of diagnosis, the patient had developed many of the symptoms associated with her disease, including chronic kidney disease, rickets, and myopathy that left her non-ambulatory. During her initial evaluation, she was also noted to have hepatocellular carcinoma. With cadaveric liver transplantation and nutritional support, her symptoms all either resolved or stabilized. Her case illustrates the severity of the disease if left untreated, the need for vigilance in populations who do not routinely receive newborn screens, and the markedly improved outcomes in patients following transplant.

Liver Cancer in Tyrosinemia Type 1

Hereditary Tyrosinemia type I (HT1) is clinically mainly characterised by severe liver disease. Most patients present in their first months of life with liver failure, but others can present later with issues of compensated cirrhosis, renal tubulopathy or acute intermittent porphyria. If patients survive the acute phase with liver failure or if they present later with compensated cirrhosis, they often develop hepatocellular carcinoma early but also later in life. The course of the disease changed after the introduction of 2-(2 nitro-4-3 trifluoro-methylbenzoyl)-1, 3-cyclohexanedione (NTBC), which blocks the tyrosine degradation pathway at an earlier step. Therefore, the toxic products did not accumulate anymore and all clinical problems resolved. However, the risk (although clearly decreased) for developing liver cancer remained, especially if NTBC treatment is initiated late, a slow decrease of the tumor marker α-fetoprotein is seen or if the α-fetoprotein concentrations remain just above the normal range. A rise of α-fetoprotein in these HT1 patients is more or less pathognomonic for liver cancer. Although hepatoblastoma development occurs in HT1 patients, most HT1 patients develop hepatocellular carcinoma (HCC) or a mixed type of carcinoma consisting of HCC and hepatoblastoma. Due to the small risk of liver cancer development, screening for liver cancer (especially HCC) is still recommended in HT1 patients using regular measures of α-fetoprotein and imaging. Ultrasound is mostly the modality of choice for surveillance, because it is widely available, it does not use radiation and is noninvasive. When a suspicious lesion is present, the higher sensitivity of MRI could be used for characterization and staging of lesions. At this moment, no HCC development in pre-symptomatically treated patients is reported. These different situations could possibly indicate that NTBC can prevent the start of the development of HCC when initiated early, but can't stop the development of HCC if it is prescribed at a later stage, stressing the importance of early diagnosis.

The Liver in Tyrosinemia Type I: Clinical Management and Course in Quebec

HT1 is a severe autosomal recessive disorder due to the deficiency of fumarylacetoacetate hydrolase (FAH), the final enzyme in the degradation of tyrosine. Before the era of treatment with 2-(2-N-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), even with newborn screening and optimal diet therapy, HT1 patients often developed liver failure. Death was common in patients who did not undergo liver transplantation. For the last two decades, NTBC has revolutionized the management of HT1 patients. In screened newborns treated within the first month of life, we have not observed hepatocarcinoma. If patients are not detected at birth by neonatal screening, the diagnosis and treatment must be performed on an emergency basis, and patients are at risk for complications. Long term adhesion to treatment and reliable early detection of hepatocellular carcinoma (HCC) are two important challenges. In this chapter, we describe the clinical, biological, histo-pathological and imaging findings of HT1 in Québec before the era of NTBC. We also describe the hepatic status of nontransplanted tyrosinemic patients in Quebec and current management practices in the Quebec NTBC Study.

Neonatal Screening for Inherited Metabolic Diseases in 2016

The scope of newborn screening (NBS) programs is continuously expanding. NBS programs are secondary prevention interventions widely recognized internationally in the "field of Public Health." These interventions are aimed at early detection of asymptomatic children affected by certain diseases, with the objective to establish a definitive diagnosis and apply the proper treatment to prevent further complications and sequelae and ensure a better quality of life. The most significant event in the history of neonatal screening was the discovery of phenylketonuria in 1934. This disease has been the paradigm of inherited metabolic diseases. The next paradigm was the introduction of tandem mass spectrometry in the NBS programs that make possible the simultaneous measurement of several metabolites and consequently, the detection of several diseases in one blood spot and in an unique analysis. We aim to review the current situation of neonatal screening in 2016 worldwide and show scientific evidence of the benefits for some diseases. We will also discuss future challenges. It should be taken into account that any consideration to expand an NBS panel should involve a rigorous process of decision-making that balances benefits against the risks of harm.

Pathology of the liver in children: Where would I (we) be without "Pepper"?

A tribute to Pepper's lasting contributions to Hepatopathology.

Outcome of children with hereditary tyrosinaemia following newborn screening

BACKGROUND

Nitisinone has transformed the management of hereditary tyrosinaemia type 1 (HT1). However, the risk of developing hepatocellular carcinoma is related to the age at which treatment is commenced. Little data on the outcome of children treated pre-emptively exist.

AIM

To describe the outcome of children with HT1 treated with nitisinone following selective newborn screening (NBS) and to compare their outcome with index siblings who had presented clinically.

SUBJECTS

12 children with HT1 were detected by NBS. Seven children were screened for HT1 because of an affected sibling (n=5). Four children were detected due to raised tyrosine concentrations on routine NBS and one child was born in a country with universal NBS for HT1.

OUTCOME

Nitisinone was commenced at 4 (1-52) days old. 6 children had an initial coagulopathy which resolved after 4 (1-7) days treatment. Currently at median age 8.5 (3-12.5) years all are clinically normal, with normal liver function tests and imaging. Those of school age are in normal classes but four have reported learning difficulties. Five index siblings presented clinically with acute liver failure (four) and chronic liver disease (one) at median 4 (1.5-17) months. One died of liver failure prior to nitisinone's availability. Four were treated with nitisinone; one failed to respond and underwent liver transplantation and three responded. One responder died from complications of prematurity and the remaining two have compensated liver disease.

SUMMARY

Children with HT1 treated with nitisinone following NBS have an excellent outcome.

CONCLUSIONS

Universal NBS for HT1 should be introduced in the UK.

Liver Transplant for Children With Hepatocellular Carcinoma and Hereditary Tyrosinemia Type 1

OBJECTIVES

This study sought to determine the prevalence of hepatocellular carcinoma and other premalignant lesions in children with hereditary tyrosinemia type 1 who had undergone an orthotopic liver transplant at the Shiraz Transplant Center, in Shiraz, Iran.

MATERIALS AND METHODS

Between September 2006, and June 2011, thirty-six patients with hereditary tyrosinemia type 1 received a liver transplant from a deceased (whole or split) or a living-related donor. Clinical records and pathologic specimens, before and after surgery, for each case were reviewed. In addition, ultrasound, abdominal computed tomographic imaging scan findings, and levels of alpha-fetoprotein were recorded.

RESULTS

Twenty-two patients with hepatic nodules larger than 10 mm underwent a Tru-Cut needle biopsy before their liver transplant. In 2 patients, a diagnosis of hepatocellular carcinoma was made by pathologic examination; in the other 20, cirrhosis was confirmed with no evidence of malignancy. After pathologic examination of the explanted livers, the largest nodules in the 36 patients were 35 mm. Five cases had at least 1 nodule of hepatocellular carcinoma. Three of the other patients had small cell dysplasia in some of nodules. All 5 cases with hepatocellular carcinoma were patients older than 2 years of age (19 patients were older than 2 years of age). All patients with hepatocellular carcinoma received pretransplant nitisinone treatment. All patients with hepatocellular carcinoma after their liver transplant are alive at the time of this writing.

CONCLUSIONS

The prevalence of cell dysplasia and hepatocellular carcinoma in children with hereditary tyrosinemia type 1 in our study is not as high as that reported previously, so it appears that patients older than 2 years of age require a liver transplant.

Nonalcoholic Steatohepatitis: Diagnostic Challenges

This article reviews diagnostic criteria for nonalcoholic steatohepatitis (NASH), current grading and staging methodology, and diagnostic challenges and pitfalls in routine practice. Current practice guidelines and prognostic and treatment considerations are discussed. The clinical diagnosis of nonalcoholic fatty liver disease may represent stable disease without progressive liver damage, in the form of nonalcoholic fatty liver (NAFL), or aggressive disease that will progress to advanced fibrosis, in the form of NASH. NASH is diagnosed from a liver biopsy after assessment by a pathologist to distinguish NASH from NAFL (and other histologic mimics of NASH); this distinction is critical for patient management.

Activation of nuclear factor E2-related factor 2 in hereditary tyrosinemia type 1 and its role in survival and tumor development

In tyrosinemia type 1 (HT1), accumulation of toxic metabolites results in oxidative stress and DNA damage, leading to a high incidence of hepatocellular carcinomas. Nuclear factor erythroid-2 related factor 2 (Nrf2) is a key transcription factor important for cellular protection against oxidative stress and chemical induced liver damage. To specifically address the role of Nrf2 in HT1, fumarylacetoacetate hydrolase (Fah)/Nrf2(-/-) mice were generated. In acute HT1, loss of Nrf2 elicited a strong inflammatory response and dramatically increased the mortality of mice. Following low grade injury, Fah/Nrf2(-/-) mice develop a more severe hepatitis and liver fibrosis. The glutathione and cellular detoxification system was significantly impaired in Fah/Nrf2(-/-) mice, resulting in increased oxidative stress and DNA damage. Consequently, tumor development was significantly accelerated by loss of Nrf2. Potent pharmacological inducers of Nrf2 such as the triterpenoid analogs 1[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole have been developed as cancer chemoprevention agents. Pretreatment with 1[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole dramatically protected Fah(-/-) mice against fumarylacetoacetate (Faa)-induced toxicity. Our data establish a central role for Nrf2 in the protection against Faa-induced liver injury; the Nrf2 regulated cellular defense not only prevents acute Faa-induced liver failure but also delays hepatocarcinogenesis in HT1.

Current strategies for the treatment of hereditary tyrosinemia type I

Hereditary tyrosinemia type I (HT-I) is the most common of the three known diseases caused by defects in tyrosine metabolism. This type of tyrosinemia is caused by a mutation in the gene coding for fumarylacetoacetate hydrolase; several mutations in this gene have been identified. The main clinical features of HT-I are caused by hepatic involvement and renal tubular dysfunction. Dietary intervention with restriction of phenylalanine and tyrosine together with supportive measures can ameliorate the symptoms, but given the high risk for hepatocellular carcinoma, a cure for these patients has so far been possible only with liver transplantation. Pharmacologic treatment with nitisinone, a peroral inhibitor of the tyrosine catabolic pathway, offers an improved means of treatment for patients with HT-I. However, longer follow-up periods are needed to establish the role of this drug in ultimately protecting patients from end-stage organ involvement and hepatocellular carcinoma. Experimental work in mice has provided some promise for the future management of tyrosinemia with gene therapy.

The efficacy of liver transplantation in malignant liver tumors associated with tyrosinemia: clinical and laboratory findings of five cases

To evaluate clinical and laboratory findings of these patients and the efficacy of liver transplantation in children with hepatocellular carcinoma (HCC) and hepatoblastoma (HB) associated with tyrosinemia. Among 113 children with liver tumors diagnosed between 1972 and 2004 five patients had HCC or HB associated with tyrosinemia. The age at diagnosis of the HCC or HB ranged from 9.5 to 17 yr and male:female ratio was 1:4. During regular clinic visits for tyrosinemia, elevated alpha-fetoprotein (AFP) was detected in all patients. AFP levels ranged between 13.7 and 29 340 IU/mL. Radiological studies including ultrasound, computed tomography and magnetic resonance imaging showed heterogeneous parenchyma and nodules in the liver. The patients did not have any metastatic disease. The time from diagnosis of tyrosinemia to HCC or HB ranged from 9.25 to 15.25 yr. Histopathologically, four patients have been diagnosed as HCC and one patient had HB. All patients were given chemotherapy including cisplatin and adriamycin. In three patients, living-related liver transplantation was performed. They had no treatment after transplantation. All of them are disease free. One patient was treated with chemotherapy and right hepatectomy. She had no suitable donor for living-related liver transplantation. Three months after completing chemotherapy, she had recurrent tumor in the left lobe of the liver and she died with progressive disease. The last patient whose parents were not suitable as donors for living-related liver transplantation is waiting for a deceased donor graft. All patients had limited disease to liver due to close clinical and radiological follow up for tyrosinemia. In these patients liver transplantation is curative both for liver tumor and tyrosinemia.

Hepatocellular carcinoma in children and effect of living-donor liver transplantation on outcome

Hepatocellular carcinoma (HCC) is primarily observed in the older children and in most cases it develops in association with liver cirrhosis. Liver transplantation offers a good chance for long-term cure. To evaluate the outcome of children with HCC and the impact of living-donor orthotopic liver transplantation (OLT) on survival a retrospective review of radiographic, laboratory, pathologic, and therapeutic data in 13 children (six female and seven male) with chronic liver disease accompanied with HCC were studied. The patients were divided into two groups according to therapeutic modality: transplanted and non-transplanted patients. Kaplan-Meier survival curves in various therapeutic groups were plotted. The mean age of patients was 6.4 +/- 4.8 yr. Pediatric end-stage liver disease score was adapted to model for end-stage liver disease score for HCC and ranged between 1-44 and 18-44, respectively. The underlying liver diseases were tyrosinemia type 1 (n = 6), chronic hepatitis B infection (n = 6), glycogen storage disease type 1 (n = 1). Alfa-feto protein levels were elevated in all patients except one. Median number of tumor nodules was three (1-10), median maximal diameter of tumor nodules was 3.4 cm (0.5-8). Eleven patients were eligible for OLT whereas two patients were not eligible. Seven of the 11 patients considered for transplantation underwent living-donor OLT. Remaining four patients died while waiting on cadaveric transplant list. Overall 1 and 4-yr survival rates for all patients were 53.3 and 26.6%, respectively, and were found significantly higher in transplanted children than non-transplanted children (72%, 72% vs. 33% and 16.6%). No patient had tumor recurrence at median of 36-month follow-up after OLT. OLT is a life-saving procedure for children with chronic liver disease accompanying with HCC. Living-donor OLT avoids the risk of tumor progression and transplant ineligibility in these children.

Epidemiology and carcinogenesis of hepatocellular carcinoma

The incidence of hepatocellular carcinoma (HCC) shows marked variation worldwide but the magnitude of this tumor is reflected by the occurrence of at least 1 million new cases annually and the uniformly dismal outlook with median survivals of <25 months after resection and <6 months with symptomatic treatment. The strikingly uneven distribution of this tumor parallels the prevalence of hepatitis B infection with rising incidence in western countries attributed to hepatitis C infection. Chronic hepatitis and cirrhosis constitute the major preneoplastic conditions in the majority of HCCs and may be related to other etiologic agents such as environmental chemical carcinogens including nitrites, hydrocarbons, solvents, organochlorine pesticides, and the chemicals in processed foods, cleaning agents, cosmetics and pharmaceuticals, as well as plant toxins such as anatoxins produced by fungi that cause spoilage of grain and food in the tropics. Genetic diseases such as genetic hematochromatosis, Wilson's disease, alpha-1-antitrypsin deficiency, and the inborn errors of metabolism including hereditary tyrosinemia and hepatic porphyria, are known to be associated with HCC. Numerous genetic alterations and the modulation of DNA methylation are recognized in HCC and it is likely that these genetic and epigenetic changes combine with factors involved in chronic hepatocyte destruction and regeneration to result in neoplastic growth and multiple molecular pathways may be involved in the production of subsets of hepatocellular tumors.

Inherited metabolic diseases of the liver

Many inherited metabolic diseases affect the liver in neonates, children, or adults. The histopathologic changes are diverse and may be acute or chronic. They can be considered primary (when the injury is from the cytopathic effect of an accumulated metabolite) or secondary (e.g., an infection caused by an immune deficiency). All forms of liver disease are described: for example, intrahepatic cholestasis, neonatal hepatitis with giant-cell transformation, paucity of bile ducts, steatosis, steatohepatitis, necroinflammatory diseases (acute or chronic), fibrosis, cirrhosis, and neoplasms (benign or malignant). Familiarity with the morphologic changes is important in clinicopathologic correlation, diagnosis, and understanding of pathogenetic mechanisms.

Hepatocellular kinetics and the expression of growth hormone (GH) in the livers and liver tumours of GH-transgenic mice

Although it is well known that transgenic mice that overexpress growth hormone (GH) frequently develop liver tumours, the precise nature of the relationship between the overexpression of GH and hepatocarcinogenesis is not clear. The current study was designed to investigate the relationship between the expression of the GH transgene and changes in hepatocyte morphology and kinetics, prior to and during hepatocarcinogenesis in GH-transgenic mice. In young mice (1-month-old) prior to tumour development, GH protein, as detected by immunohistochemistry, was observed in the cytoplasm of essentially all hepatocytes. In liver tissues of older animals, apoptotic cells and hypertrophic hepatocytes did not express immunoreactive GH, even though GH was expressed strongly in the smaller hepatocytes. A relatively high proportion of large dysplastic hepatocytes (>50 microm) were apoptotic (TUNEL positive), whereas smaller hepatocytes featured more prominently in the proliferative phase, as measured by BrdU incorporation. GH expression in tumour tissue, as detected by immunohistochemistry, was often variable and generally decreased with tumour development. Northern blot analysis showed that equivalent levels of GH mRNA were present in tumour tissue and adjacent liver. However, there was no clear trend when the levels of GH mRNA extracted from adenoma, and hepatocellular carcinoma, were compared. These observations help clarify some of the mechanisms by which GH promotes hepatocarcinogenesis in GH-transgenic mice.

Tyrosinemia: a review

Hypertyrosinemia encompasses several entities, of which tyrosinemia type I (or hepatorenal tyrosinemia, HT1) results in the most extensive clinical and pathological manifestations involving mainly the liver, kidney, and peripheral nerves. The clinical findings range from a severe hepatopathy of early infancy to chronic liver disease and rickets in the older child; gradual refinements in the diagnosis and medical management of this disorder have greatly altered its natural course, mirroring recent advances in the field of metabolic diseases in the past quarter century. Hepatorenal tyrosinemia is the inborn error with the highest incidence of progression to hepatocellular carcinoma, likely due to profound mutagenic effects and influences on the cell cycle by accumulated metabolites. The appropriate follow-up of patients with cirrhosis, the proper timing of liver transplantation in the prevention of carcinoma, and the long-term evolution of chronic renal disease remain important unresolved issues. The introduction of a new pharmacologic agent, NTBC, holds the hope of significantly alleviating some of the burdens of this disease. Mouse models of this disease have permitted the exploration of newer treatment modalities, such as gene therapy by viral vectors, including ex vivo and in utero methods. Finally, recent observations on spontaneous genetic reversion of the mutation in HT1 livers challenge conventional concepts in human genetics.

Hereditary tyrosinaemia type I: from basics to progress in treatment

Hereditary tyrosinaemia type I is the most common of the diseases caused by defects in tyrosine metabolism. The underlying genetic defect is a mutation in the gene for fumarylacetate hydrolase (FAH), and more than 30 different mutations in this gene have been identified. The main clinical consequences of this defect include hepatic involvement, with a high risk for liver cancer, and renal tubular dysfunction. Restriction of phenylalanine and tyrosine from the diet along with supportive measures can ameliorate the symptoms, but cure has so far been possible only with liver transplantation. Recent discovery of a pharmacological treatment with a peroral inhibitor of tyrosine catabolic pathway, 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), offers a new promising tool for the treatment of patients with hereditary tyrosinaemia type I. Mouse models of FAH deficiency have been successfully used in experimental gene therapy, and these studies indicate that future management of tyrosinaemia with a gene therapeutic approach may become feasible.

Deficient DNA-ligase activity in the metabolic disease tyrosinemia type I

Hereditary tyrosinemia type I (HT1) is an autosomal recessive inborn error of metabolism caused by the deficiency of fumarylacetoacetate hydrolase, the last enzyme in the tyrosine catabolism pathway. This defect results in accumulation of succinylacetone (SA) that reacts with amino acids and proteins to form stable adducts via Schiff base formation, lysine being the most reactive amino acid. HT1 patients surviving beyond infancy are at considerable risk for the development of hepatocellular carcinoma, and a high level of chromosomal breakage is observed in HT1 cells, suggesting a defect in the processing of DNA. In this paper we show that the overall DNA-ligase activity is low in HT1 cells (about 20% of the normal value) and that Okazaki fragments are rejoined at a reduced rate compared with normal fibroblasts. No mutation was found by sequencing the ligase I cDNA from HT1 cells, and the level of expression of the ligase I mRNA was similar in normal and HT1 fibroblasts, suggesting the presence of a ligase inhibitor. SA was shown to inhibit in vitro the overall DNA-ligase activity present in normal cell extracts. The activity of purified T4 DNA-ligase, whose active site is also a lysine residue, was inhibited by SA in a dose-dependent manner. These results suggest that accumulation of SA reduces the overall ligase activity in HT1 cells and indicate that metabolism errors may play a role in regulating enzymatic activities involved in DNA replication and repair.

Histopathologic approach to metabolic liver disease: Part 2

In this, part 2 of the histopathologic approach to the diagnosis of metabolic disease of the liver, the steatotic, cirrhotic, and neoplastic groups are addressed. See the previous issue, Volume 1, Number 3, of Pediatric and Developmental Pathology for part 1 [1]. The perspective concludes with a tabulated assessment of the likelihood of diagnostic ascertainment.

Chemistry and biology of heme. Effect of metal salts, organometals, and metalloporphyrins on heme synthesis and catabolism, with special reference to clinical implications and interactions with cytochrome P-450

Although free porphyrins occur in nature in small quantities, no known function has been assigned to them. In contrast, heme and cobalamin, which are Fe and Co chelates of porphyrins or porphyrin derivatives, respectively, carry out crucial biological functions. Heme is the prosthetic group for a number of hemoproteins. These include myoglobin and hemoglobin, which carry out oxygen binding or transport; mitochondrial cytochromes aa3, b, c, and c3, which are important in transferring electrons; microsomal cytochrome P-450, which catalyzes mixed-function oxidations; catalase, which decomposes H2O2; peroxidase, which activates H2O2; and tryptophan pyrrolase, which catalyzes the oxidation of tryptophan. Recently, heme has also been shown to be the prosthetic group of prostaglandin and peroxide synthetase and indoleamine dioxygenase. The elegant studies of the biochemical pathway for the formation of heme demonstrated the arrangement in the porphyrin macrocycle of the carbon and nitrogen atoms originating from the eight glycine and the succinic acid molecule that are the precursors of porphyrins. There are eight enzymes involved in the synthesis of heme. The first and last three of these enzymes are localized in mitochondria, while the intermediate enzymes are localized in cytosol. The catalytic site of HMOX recognizes metalloporphyrins with central metal atoms other than iron; it favors some of these metalloporphyrins over heme as a potential substrate, sometimes by a large factor, permitting the synthetic heme analogue to serve as a potent competitive inhibitor of HMOX reaction. Since these synthetic metalloporphyrins do not bind molecular oxygen, they are not metabolically degraded by ring rupture and do not add to the body pool of bile pigment. One possible consequence of this competitive inhibition of heme degradation is suppression of bile pigment formation to such a degree that excessive plasma levels of bilirubin may be diminished. The studies of Drummond and Kappas (1981) and later studies in rats, mice, monkeys, and man, and also our studies have proved the latter phenomenon. The compound does not appear to affect the metabolic disposition of preformed bilirubin but inhibits biliary bilirubin excretion derived from the metabolism of endogenous or exogenous heme. Whether some of the effect of Sn-PP on naturally occurring or experimentally induced jaundice in animals reflects diversion of heme to nonheme to oxygenase-dependent pathways of heme metabolism, or whether a pathway which is normally latent becomes activated concurrent with HMOX inhibition is not known.(ABSTRACT TRUNCATED AT 400 WORDS)

Deficiency of an enzyme of tyrosine metabolism underlies altered gene expression in newborn liver of lethal albino mice

Mice homozygous for albino deletions encompassing the locus alf/hsdr-1 die shortly after birth. Lethality is thought to be the consequence of hypoglycemia, which results from the failure to activate hormone-dependent genes in liver and kidney encoding enzymes important for gluconeogenesis. Within the region in which alf/hsdr-1 has been defined by physical mapping, we identified the gene encoding fumarylacetoacetate hydrolase (FAH), an enzyme of tyrosine metabolism. Lack of FAH activity should lead to accumulation of toxic tyrosine metabolites. In man, genetically determined FAH deficiency is the primary defect in tyrosinemia type I, a fatal liver disease of infants. Northern blot and in situ hybridization analysis of mouse tissues showed that the cell types that normally express FAH correspond to those that exhibit a phenotype in alf/hsdr-1 deletion mice. Moreover, we could mimic aspects of the alf/hsdr-1 deletion phenotype in vitro by treating primary hepatocyte cultures with an intermediate of tyrosine metabolism. These findings strongly suggest that alf/hsdr-1 encodes FAH and that absence of FAH is responsible for neonatal lethality in albino deletion mice. Mechanisms by which this metabolic defect might bring about alterations in gene expression characteristic of the alf/hsdr-1 deletion phenotype are discussed.

Orthotopic liver transplantation in liver-based metabolic disorders

The efficacy of orthotopic liver transplantation (OLT) in the management of more common liver-based metabolic disorders associated with severe liver damage, alpha-1-antitrypsin deficiency (PIZZ), Wilson disease and tyrosinaemia has been demonstrated and indications defined. An early mortality in excess of 15% and finite resources limit its use. Phenotypic heterogeneity make the precise indication in other disorders less certain. In disorders in which endstage liver disease is less frequent such as cystic fibrosis, haemochromatosis and galacosaemia it has been a very effective therapy. It has been used with encouraging results in disorders in which the liver is structurally normal such as Crigler-Najjar type I, primary hyperoxaluria type I and primary hypercholesterolaemia. In these it should be performed before there is permanent damage to brain, kidneys or heart. OLT in the short term prevents hyperammonaemic coma in urea cycle defects and may prevent extrahepatic disease in glycogen storage disease type IV. Its limitation in reversing all metabolic effects in these and other disorders is discussed. It is ineffective in protoporphyria or Niemann Pick disease type II (Sea Blue Histiocyte syndrome) in which the transplanted liver acquires the lesions of the initial disorder and extrahepatic features progress. Early referral provides optimum circumstances to assess the benefits of OLT as compared with those of other forms of management and to achieve transplantation at the ideal time. The place of OLT in management will require constant review as metabolic disorders are better defined, new forms of therapy evolve and as techniques of liver transplantation and modes of immunosuppression improve.

Treatment of inherited metabolic disorders by liver transplantation

Among the worldwide accepted indications for liver transplantation, inherited metabolic disorders play an increasing role. In some paediatric centres this indication runs second after extrahepatic biliary atresia. The aim of liver transplantation in inherited metabolic disorders is twofold: the first is to save a patient's life, the second is to accomplish phenotypic and functional cure of his disease. These aims may be achieved in disorders presenting with cirrhosis, hepatoma, life-threatening progression or failure of other organs with preserved liver function. The timing of liver transplantation has become easier with development of surgical techniques of reduced-size donor livers. These techniques enable the performance of liver transplantation with ABO blood group compatible organs of almost any size if indicated either by deterioration of liver function or impending complications such as hepatoma or life-threatening progression. In comparison with other indications such as extrahepatic biliary atresia, postnecrotic liver cirrhosis or acute liver failure, the results of transplantation in patients with inherited metabolic disorders seem to be better, reaching up to 78-95% actuarial 1-year survival rates. However, lifelong immunosuppressive therapy is necessary. This seems to be acceptable even in disorders with only partial liver function defects.

Tyrosinaemia type I--an update

Tyrosinaemia type I is a recessively inherited disorder caused by a deficiency of fumarylacetoacetase (FAH), the last enzyme in tyrosine degradation. The presumed toxic agents are fumaryl- and maleylacetoacetate which are converted to succinylacetone (SA), a metabolite found in increased amounts in urine and plasma of the patients. The major clinical features are progressive liver damage and renal tubular defects with hypophosphataemic rickets. Renal tubular dysfunctions with secondary rickets may be lacking altogether, even in chronic patients. Hepatocellular carcinoma is a major cause of death in the chronic form. Diagnosis of the disorder is made by assay of SA in urine and serum and by determination of FAH in lymphocytes or fibroblasts. Prenatal diagnosis is performed by SA assay in amniotic fluid supernatant and FAH analysis in cultured amniotic fluid cells or chorionic villus material. Presence of a 'pseudodeficiency' gene for FAH prevents prenatal diagnosis by enzyme analysis in some families, and this gene also precludes identification of heterozygotes outside tyrosinaemia families. Immunoblot analyses show that acute patients and some chronic patients lack immunoreactive FAH protein. cDNA probes for FAH have been developed and several polymorphisms related to the FAH gene have been reported, which may allow prenatal diagnosis in families with complex genotypes. The gene for FAH has been mapped to chromosome 15 q23-q25. Liver transplantation is the ultimate treatment; most patients continue to excrete SA in urine after liver transplantation and therefore there is a possibility of kidney disease after transplantation.

Liver transplantation for metabolic disorders

Liver transplantation for metabolic disorders continues to be an expanding field, both in the range of indications and patient numbers. In most large series it accounts for approximately 7% of all adult transplants and 29% of all childhood transplants. As the results of medical therapy are improved so too are the results of liver transplantation, and hence more patients are being considered for the latter therapy. The benefits of this treatment are not only the prolongation of and improvement in the quality of life for the patient, it has also given insight into the basic metabolic defects of many disorders.