Liver transplantation in two children with tyrosinaemia type I: biochemical aspects

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.

Tyrosinemia type 1: metastatic hepatoblastoma with a favorable outcome

The clinical course of tyrosinemia type 1 is characterized by acute liver failure in infancy or chronic liver dysfunction and renal Fanconi syndrome in late-presenting cases. Dietary treatment may improve liver function but does not prevent the development of hepatocellular carcinoma (HCC) in late childhood. A new treatment strategy that uses 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), which prevents the production of toxic/carcinogenic metabolites, has dramatically changed the outcome of the disease by reducing the occurrence of liver cancer, especially in patients who start this treatment before the age of 2 years. We report here the case of a patient with a diagnosis of tyrosinemia type 1 at 5 months of age who was treated with NTBC and dietary restriction and in whom a liver neoplasm with lung metastases, histologically determined to be HCC, was found at the age of 15 months. A conservative approach that consisted of chemotherapy and partial hepatectomy resulted in a 12-year disease-free period. The excellent postchemotherapy course, in sharp contrast to the expected course of HCC, led to histologic reevaluation with reclassification of the neoplasm as hepatoblastoma. A diagnosis of hepatoblastoma would no longer be a mandate for a liver transplant for patients with tyrosinemia type 1 undergoing NTBC treatment. We encourage clinicians to perform more accurate evaluation of liver histology, because a neoplastic mass in a child with tyrosinemia type 1 is not the same as HCC.

Splicing mutations, mainly IVS6-1(G>T), account for 70% of fumarylacetoacetate hydrolase (FAH) gene alterations, including 7 novel mutations, in a survey of 29 tyrosinemia type I patients

Hereditary tyrosinemia type I (HTI) is an autosomal recessive disease characterized by a deficiency in fumarylacetoacetate hydrolase (FAH) activity. In this work, the FAH genotype was established in a group of 29 HTI patients, most of them from the Mediterranean area. We identified seven novel mutations-IVS8-1(G>A, IVS10-2(A>T), 938delC, E6/I6del26, W78X, Q328X, and G343W-and two previously described mutations-IVS6-1(G>T) and IVS12+5(G>A). Fully 92.8% of the patients were carriers of at least one splice site mutation, with IVS6-1(G>T) accounting for 58.9% of the total number of alleles. The splice mutation group of patients showed heterogeneous phenotypic patterns ranging from acute forms with severe liver malfunction to chronic forms with renal manifestations and slow progressive hepatic alterations. Qualitative FAH cDNA expression was the same in all IVS6-1(G>T) homozygous patients regardless of their clinical picture. One patient with a heterozygous combination of a nonsense (Q328X) and a frameshift (938delC) mutation showed an atypical clinical picture of hypotonia and repeated infections. Despite the high prevalence of IVS12+5(G>A) in the northwestern European population, we found only two patients with this mutation in our group.

Therapeutic trials in the murine model of hereditary tyrosinaemia type I: a progress report

We have studied a knockout mouse with fumarylacetoacetate hydrolase (FAH) deficiency as a model of human hereditary tyrosinaemia type (I (HT1). These mice have a phenotype very similar to the human disease, which is characterized by acute hepatic failure, renal tubular disease and hepatocarcinoma. We have previously reported on the efficacy of 2-(2-nitro-4-trifluoromethylbenzyol)-1,3-cyclohexanedione (NTBC) in preventing acute liver disease in HT1 mice. Here we present a progress report on long-term follow up (> 1 year) of high-dose NTBC therapy in combination with tyrosine restriction. In vivo retroviral gene therapy was also effective in abolishing the acute liver failure of HT1. Retrovirally treated mice remained completely healthy and active for 12 months after retroviral gene transfer. However, hepatocarcinoma developed in 2/3 treated animals after 1 year. Southern blot analysis showed that the tumours did not arise from retrovirally transduced hepatocytes but from non-corrected FAH-deficient cells. These results highlight the extreme danger for tumour formation in HT1 and indicate the need for improved gene therapy that leads to the elimination of endogenous FAH-deficient liver cells.