Tyrosinaemia type I and hypertrophic obstructive cardiomyopathy

Long-Term Outcomes and Practical Considerations in the Pharmacological Management of Tyrosinemia Type 1

Tyrosinemia type 1 (TT1) is a rare metabolic disease caused by a defect in tyrosine catabolism. TT1 is clinically characterized by acute liver failure, development of hepatocellular carcinoma, renal and neurological problems, and consequently an extremely poor outcome. This review showed that the introduction of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) in 1992 has revolutionized the outcome of TT1 patients, especially when started pre-clinically. If started early, NTBC can prevent liver failure, renal problems, and neurological attacks and decrease the risk for hepatocellular carcinoma. NTBC has been shown to be safe and well tolerated, although the long-term effectiveness of treatment with NTBC needs to be awaited. The high tyrosine concentrations caused by treatment with NTBC could result in ophthalmological and skin problems and requires life-long dietary restriction of tyrosine and its precursor phenylalanine, which could be strenuous to adhere to. In addition, neurocognitive problems have been reported since the introduction of NTBC, with hypothesized but as yet unproven pathophysiological mechanisms. Further research should be done to investigate the possible relationship between important clinical outcomes and blood concentrations of biochemical parameters such as phenylalanine, tyrosine, succinylacetone, and NTBC, and to develop clear guidelines for treatment and follow-up with reliable measurements. This all in order to ultimately improve the combined NTBC and dietary treatment and limit possible complications such as hepatocellular carcinoma development, neurocognitive problems, and impaired quality of life.

Evaluation of cardiac manifestations in pediatric liver transplant candidates

Knowledge concerning the involvement of the cardiovascular system in children awaiting liver transplant is limited. Therefore, no guidelines have been established on evaluating this group of patients for cardiac disease. This review examines the diverse cardiovascular manifestations of liver disease in children. We also discuss the available testing and its applicability in screening for cardiac disease in this vulnerable population.

Cardiomyopathy in tyrosinaemia type I is common but usually benign

Tyrosinaemia type I (TTI) is an inherited multisystemic disorder of tyrosine metabolism. In addition to hepatic and renal involvement, cardiomyopathy is an important clinical manifestation.

OBJECTIVE

To evaluate the incidence and outcome of cardiomyopathy in TTI.

SUBJECTS AND METHODS

A retrospective study was performed of 20 consecutive children with TTI (12 male, 8 female) referred to a single centre between 1986 and 2002. All were initially treated with standard dietary therapy and, since 1992, with nitisinone. The indications for orthotopic liver transplantation (LT) changed during the study. Serial echocardiography was undertaken in all subjects.

RESULTS

9/20 (45%) children had an acute hepatic presentation. Five (25%) received dietary treatment followed by LT, and 14 (70%) were treated with nitisinone at presentation. 6/20 (30%) had cardiomyopathy at initial assessment, with interventricular septal hypertrophy being the commonest finding (5/6). Cardiomyopathy was significantly less common in those treated initially with nitisinone. After a median follow-up of 3.6 (0.45-13.5) years, 5/6 (83%) had complete resolution of cardiomyopathy and 1/6 showed significant improvement. No child with a normal initial echocardiography subsequently developed cardiomyopathy.

CONCLUSION

Cardiomyopathy is a common manifestation of TTI and it has a favourable long-term outcome. Children initially treated with nitisinone are less likely to develop this complication.

Successful treatment of severe cardiomyopathy with NTBC in a child with tyrosinaemia type I

We report the case of a child who developed severe obstructive hypertrophic cardiomyopathy revealing hereditary tyrosinaemia type I, who was successfully treated with NTBC. The mechanisms underlying the association are discussed.

Carnitine-deficient myopathy as a presentation of tyrosinemia type I

Carnitine deficiency secondary to renal Fanconi's tubulopathy has been described in only a few inborn errors of metabolism: cystinosis, galactosemia, and Fanconi-Bieckel syndrome. We report a 27-month-old infant who presented with a sudden change in gait owing to proximal muscle weakness. The laboratory evaluation showed carnitine deficiency associated with Fanconi's tubulopathy. Eventually, tyrosinemia type I was diagnosed. Carnitine deficiency can contribute to the clinical picture of hepatorenal tyrosinemia and should therefore be evaluated and treated.

Liver repopulation for the treatment of metabolic diseases

Orthotopic liver transplantation is the treatment of choice for several inborn errors of metabolism. Unfortunately, the supply of donor organs is limiting and therefore many patients cannot benefit from this therapy. In contrast, hepatocyte transplantation could potentially overcome the shortage in donor livers by use of cells from a single donor for multiple recipients. In classic hepatocyte transplantation, however, only 1% of the liver mass or less can be replaced by donor cells. Recently, though, it has been shown in animal models that >90% of host hepatocytes can be replaced by a small number of transplanted donor cells in a process we term 'therapeutic liver repopulation'. This phenomenon is analogous to repopulation of the haematopoietic system after bone marrow transplantation. Liver repopulation occurs when transplanted cells have a growth advantage in the setting of damage to recipient liver cells. It has been discovered that transplanted cells from extrahepatic sources such as the adult pancreas or bone marrow can also be used for liver repopulation. Because bone marrow donors are widely available, this finding raises the hope of therapeutic application of these cells in the future. Here, the current knowledge regarding therapeutic liver repopulation and the hopeful implications for treatment of liver diseases will be discussed.

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.

Pediatric gastroenterology. Update on metabolic liver disease

Wilson's disease, genetic and neonatal hemochromatosis, protoporphyria, tyrosinemia, and alpha1-antitrypsin deficiency are updated. Cost effectiveness of screening is discussed. Current therapies are evaluated, including the role of transplantation. The molecular biologic technique PCR is covered. Gene therapy is introduced.

Pharmacological correction of neonatal lethal hepatic dysfunction in a murine model of hereditary tyrosinaemia type I

Hereditary tyrosinaemia type I, a severe autosomal recessive metabolic disease, affects the liver and kidneys and is caused by deficiency of fumarylacetoacetate hydrolase (FAH). Mice homozygous for a FAH gene disruption have a neonatal lethal phenotype caused by liver dysfunction and do not represent an adequate model of the human disease. Here we demonstrate that treatment of affected animals with 2-(2-nitro-4-trifluoro-methylbenzyol)-1,3-cyclohexanedione abolished neonatal lethality, corrected liver function and partially normalized the altered expression pattern of hepatic mRNAs. The prolonged lifespan of affected animals resulted in a phenotype analogous to human tyrosinaemia type I including hepatocellular carcinoma. The adult FAH-/- mouse will serve as useful model for studies of the pathophysiology and treatment of hereditary tyrosinaemia type I as well as hepatic cancer.

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.

A pediatric perspective on liver transplantation

Liver transplantation has revolutionized the field of pediatric hepatology. The present status of this therapy is reviewed in this article from a nonsurgical perspective.