The nephropathy of type I tyrosinemia after liver transplantation

Liver Transplantation: A Safe and Definitive Alternative to Lifelong Nitisinone for Tyrosinemia Type 1

OBJECTIVES

To report the experience of liver transplantation (LT) for tyrosinemia type 1 (TT-1).

METHODS

Clinical data of children with TT-1 who underwent living donor LT between July 2009 and May 2020 were retrospectively analyzed. Data included pre-LT nitisinone therapy, graft type, post-LT complications, HCC incidence, and graft/patient survival.

RESULTS

Nine children were diagnosed with TT-1 at a median age of 12 mo (6-54 mo). Nitisinone was started in 6 patients at a median age of 15 mo (6-42 mo), but all had frequent interruption of therapy due to logistics with drug procurement including its cost. Median age at transplantation was 5 y (2-11 y). Explant liver showed HCC in 5 patients (55% of total cohort). The graft and patient survival are 100% with median follow-up of 58 mo (24-84 mo).

CONCLUSION

LT is curative for TT-1 and excellent results can be obtained in experienced centers. This is especially favorable in countries with limited resources where the cost of medical therapy is highly prohibitive, with lifelong diet restrictions and unclear long-term risk of HCC.

Living-donor liver transplantation for children with tyrosinemia type I

OBJECTIVE

To evaluate the efficacy of living-donor liver transplantation (LDLT) in children with tyrosinemia type I.

METHODS

Altogether 10 patients diagnosed with tyrosinemia type I underwent LDLT between June 2013 and April 2019. Cirrhosis was the indication for LDLT in all 10 patients, and hepatocellular carcinoma (HCC) was suspected in nine. Patients' outcomes, including liver function, restoration of metabolism, quality of life and physical development, were analyzed after LDLT.

RESULTS

All recipients were alive with a normal liver function after a median follow-up period of 49 months. Pathological examinations detected HCC in one patient, dysplasia in five and cirrhosis in all. Nine patients were found to have elevated alpha-fetoprotein level, and their median alpha-fetoprotein level dropped from 2520 ng/mL to a normal level after LDLT, with no recurrence of HCC detected during the follow-up. Tyrosine metabolism was restored to its normal level with normalized plasma tyrosine and succinylacetone concentrations. Moreover, urinary succinylacetone excretion decreased significantly during the follow up. LDLT improved patients' renal tubular function, as evidenced by the normalized plasma phosphate concentration and improved glomerular filtration rate. Severe rickets symptoms, including spontaneous fractures and bone pain, were also ameliorated. Improved motor function was reported by all patients' parents during the follow-up. Dietary restriction was no longer required, which was associated with a favorable catch-up in growth and improved quality of life. Complete resolution of hypertrophic cardiomyopathy was observed one year after LDLT in one patient.

CONCLUSION

LDLT is an effective treatment for patients with end-stage liver disease resulting from tyrosinemia type I.

Risk factors evaluation for urolithiasis among children

BACKGROUND

The prevalence of pediatric urolithiasis varies from 0.01-0.03%. Urolithiasis may be caused by anatomical, metabolic and environmental factors. Recurrence varies between 16 to 67%, and it is frequently associated with metabolic abnormalities. The objective of the present work was the identification of risk factors that promote urolithiasis in a child population.

METHODS

This study included 162 children with urolithiasis and normal renal function (mean age 7.5 years). Risk factors were investigated in two stages. In the first stage, 24-hour urine, and blood samples were analyzed to assess metabolic parameters and urinary tract infection. During the second stage, the effect of calcium restriction and a calcium load on renal Ca excretion were evaluated. Data were statistically analyzed.

RESULTS

Urolithiasis was observed in 0.02% of children, 50% of them with family history of urinary stones. There were multiple risk factors for urolithiasis including hypocitraturia (70%), hypomagnesuria (42%), hypercalciuria (37%; in 11/102 was by intestinal hyperabsorption, in 13/102 was unclassified. Ca resorption or renal Ca leak were not detected). We also detected alkaline urine (21%), systemic metabolic acidosis (20%), urinary infections (16%), nephrocalcinosis with urolithiasis (11%), oliguria (8%), urinary tract anomalies, hyperuricosemia and hypermagnesemia (7% each one), hypercalcemia (6%), hyperoxaluria (2%) and hypercystinuria (0.61%).

CONCLUSIONS

Hypocitraturia and hypomagnesuria were the most frequent risk factors associated with urolithiasis, followed by hypercalciuria. High PTH values were excluded. Children presented two or more risk factors for urolithiasis.

Early nitisinone treatment reduces the need for liver transplantation in children with tyrosinaemia type 1 and improves post-transplant renal function

BACKGROUND

Tyrosinaemia type 1 (HT1) is a rare disorder of tyrosine metabolism leading to liver failure and hepatocellular carcinoma. Treatment previously consisted of dietary restriction and orthotopic liver transplantation (OLT) but was transformed by the introduction of nitisinone in 1992. We describe the impact of nitisinone on the outcome and need for OLT in a single centre.

METHODS

A retrospective analysis was performed of patients treated for HT1 at Birmingham Children's Hospital from 1989-2009.

RESULTS

Thirty eight patients were treated during the study period. Prior to 1992 6/7 (85.7 %) underwent OLT compared to 7/31 (22.6 %) after 1992 (p = 0.004) when nitisinone treatment was available. Furthermore, nitisinone-treated patients proceeding to OLT started treatment at a median age of 428 (86-821) days compared to 52 (2-990) days in those who did not (p = 0.004). Pre-OLT calculated glomerular filtration rate (cGFR) was similar in both groups but nitisinone prevented early decline after OLT (pre-nitisinone median 99.8 to 45.8 ml/min/1.73 m2, p = 0.02 versus nitisinone-treated group median 104.3 to 89.9 ml/min/1.73 m2, p = 0.5). Urinary protein:creatinine ratio (PCR) fell post-OLT to within the normal range for those treated with nitisinone but remained elevated in those not treated with nitisinone. Tubular reabsorption of phosphate (TRP) was normal or near normal in both groups pre-OLT and post-OLT. Hypertension was commoner and more severe in those not treated with nitisinone.

CONCLUSIONS

Nitisinone reduces the need for OLT particularly when started early. For those progressing to OLT the use of prior nitisinone therapy results in a preservation of their subsequent renal function.

Monogenic diseases that can be cured by liver transplantation

While the prevalence of most diseases caused by single-gene mutations is low and defines them as rare conditions, all together, monogenic diseases account for approximately 10 in every 1000 births according to the World Health Organisation. Orthotopic liver transplantation (LT) could offer a therapeutic option in monogenic diseases in two ways: by substituting for an injured liver or by supplying a tissue that can replace a mutant protein. In this respect, LT may be regarded as the correction of a disease at the level of the dysfunctional protein. Monogenic diseases that involve the liver represent a heterogeneous group of disorders. In conditions associated with predominant liver parenchymal damage (i.e., genetic cholestatic disorders, Wilson's disease, hereditary hemochromatosis, tyrosinemia, α1 antitrypsin deficiency), hepatic complications are the major source of morbidity and LT not only replaces a dysfunctional liver but also corrects the genetic defect and effectively cures the disease. A second group includes liver-based genetic disorders characterised by an architecturally near-normal liver (urea cycle disorders, Crigler-Najjar syndrome, familial amyloid polyneuropathy, primary hyperoxaluria type 1, atypical haemolytic uremic syndrome-1). In these defects, extrahepatic complications are the main source of morbidity and mortality while liver function is relatively preserved. Combined transplantation of other organs may be required, and other surgical techniques, such as domino and auxiliary liver transplantation, have been attempted. In a third group of monogenic diseases, the underlying genetic defect is expressed at a systemic level and liver involvement is just one of the clinical manifestations. In these conditions, LT might only be partially curative since the abnormal phenotype is maintained by extrahepatic synthesis of the toxic metabolites (i.e., methylmalonic acidemia, propionic acidemia). This review focuses on principles of diagnosis, management and LT results in both paediatric and adult populations of selected liver-based monogenic diseases, which represent examples of different transplantation strategies, driven by the understanding of the expression of the underlying genetic defect.

Plasma succinylacetone is persistently raised after liver transplantation in tyrosinaemia type 1

BACKGROUND

Tyrosinaemia type 1 (HT1) is a rare disorder leading to accumulation of toxic metabolites such as succinylacetone (SA) and a high risk of hepatocellular carcinoma. Children with HT1 traditionally required liver transplantation (OLT) and while the need for this has been reduced by the introduction of nitisinone some still require OLT. SA inhibits the enzyme porphobilinogen (PBG) synthase and its activity can be used as a marker of active SA. Elevated urinary SA post OLT has been reported previously. This study describes a novel finding of elevated plasma SA following OLT for HT1.

METHODS

A retrospective analysis was performed of patients treated for HT1 at our institution from 1989-2010.

RESULTS

Thirteen patients had an OLT for HT1. In patients who received nitisinone prior to OLT, mean urinary and plasma SA were elevated prior to treatment but normalised by the time of OLT (p ≤ 0.01). Mean PBG synthase activity increased from 0.032 to 0.99 nkat/gHb (ref range 0.58-1.25) at the time of OLT (p < 0.01). Mean urinary SA in patients not treated with nitisinone was also elevated prior to OLT; plasma levels and PBG synthase activity were not available prior to OLT for this group. Following OLT, mean urinary and plasma SA were elevated in all for the duration of follow-up and associated with low-normal PBG synthase activity.

CONCLUSION

Urinary and plasma SA levels are elevated following OLT for HT1. Low-normal PBG synthase activity suggests the plasma SA may be active. The clinical significance of this is unclear.

Long term follow-up of glomerular and tubular functions in liver transplanted patients with Wilson's disease

The aim of this study was to determine the long term outcome of renal glomerular and tubular functions in children receiving an LT for WD. Renal functions were examined in nine children with WD before and long after LT and compared with those of nine liver transplanted children with hepatic diseases other than WD. The duration of follow-up was at least two yr for both groups. GFR, fractional TRP and tubular maximum rate of phosphate reabsorption in relation to GFR (TP/GFR) as well as daily protein and Ca excretion were studied in both groups before and after LT. Pretransplant mean GFR, TRP and TP/GFR were significantly lower in the study group than the controls. A significant increase in the post-transplant TRP and TP/GFR was observed in the study group and the difference between the groups disappeared during the long term follow-up. Urinary protein excretion decreased in both groups after LT. Tubular dysfunction is frequent in patients with WD. LT for hepatic failure secondary to WD is a lifesaving procedure correcting the underlying hepatic defect as well as renal defects.

Metabolic liver disease in children

The aim of this article is to provide essential information for hepatologists, who primarily care for adults, regarding liver-based inborn errors of metabolism with particular reference to those that may be treatable with liver transplantation and to provide adequate references for more in-depth study should one of these disease states be encountered.

Metabolic liver disease in children

The aim of this article is to provide essential information for hepatologists, who primarily care for adults, regarding liver-based inborn errors of metabolism with particular reference to those that may be treatable with liver transplantation and to provide adequate references for more in-depth study should one of these disease states be encountered.

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.

Kidneys of mice with hereditary tyrosinemia type I are extremely sensitive to cytotoxicity

Children with hereditary tyrosinemia type 1 (HT1) suffer from liver failure, renal tubular dysfunction, and rickets. The disease is caused by deficiency of fumarylacetoacetate hydrolase (FAH), the last enzyme of tyrosine catabolism, and leads to accumulation of the toxic substrate fumarylacetoacetate (FAA) in hepatocytes and renal proximal tubular cells. Patients are treated with 2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3 cyclohexanedione (NTBC), which prevents accumulation of FAA by blocking an enzyme upstream of FAH. Liver transplantation is performed when patients do not respond to NTBC or develop hepatocellular carcinoma. This reduces the tyrosine load for the kidney but does not abolish renal exposure to locally produced FAA. To investigate the pathogenesis of liver and kidney damage induced by tyrosine metabolites, we challenged FAH-deficient mice with various doses of homogentisic acid (HGA), a precursor of FAA. Injecting NTBC-treated Fah-/- mice with low doses of HGA caused renal damage and death of renal tubular cells, as was shown by histologic analyses and deoxynucleotidyl transferase-mediated dUDP nick-end labeling (TUNEL) assay but did not lead to liver damage. In addition, kidney function, but not liver function, was affected after exposure to low doses of HGA. Administration of high doses of HGA led to massive cell death in both the liver and kidneys. Resistance to HGA-induced cell death was seen after withdrawing NTBC from Fah-/- mice. The finding that the kidneys of Fah-/- mice are especially sensitive to damage induced by low doses of HGA underscores the need to perform careful monitoring of the kidney function of tyrosinemia patients undergoing any form of treatment.

Renal function following liver transplantation in children

The literature regarding the etiology and incidence of short and long-term renal functional impairment in pediatric liver allograft recipients was reviewed. Most of the reports include recipients receiving cyclosporine as the primary immunosuppressant. Using calculated glomerular filtration rate (cGFR), creatinine clearance or the serum creatinine level will lead to an overestimation of GFR. In contrast to data in adults, there are a limited number of pediatric recipients whose renal dysfunction has progressed to chronic kidney disease or end-state renal disease. Calcineurin inhibitors minimization has proven effective in reversing or preventing progressive deterioration of GFR; however, rejection episodes and complications have limited efficacy of this approach. Future multicenter studies using optimal GFR measurements are required to delineate the magnitude of renal dysfunction in pediatric recipients.

Glomerular and tubular function following orthotopic liver transplantation in children

Since its advent, cyclosporine nephrotoxicity has been a major concern to pediatricians attending to liver transplant recipients. The aims of this study were to examine glomerular and tubular function after orthotopic liver transplantation (OLT) in children, their correlation to CsA, and how they differed according to the underlying disease.

PATIENTS AND METHODS

Glomerular and tubular function was examined in 28 patients aged 7 months to 14 yr at the time of transplantation (mean 4.0 +/- 3.6), retrospectively examining creatinine clearance, tubular phosphate reabsorption (TRP), calcium/creatinine ratio, sodium excretion fraction, and protein/creatinine ratio. The group with metabolic disease and an underlying tubulopathy was compared with the group with liver disease only. The effect of CsA trough levels and cumulated dose on these indices was examined, as was the effect of antihypertensives on creatinine clearance. Both glomerular and tubular functions improved significantly following liver transplantation. In patients on CsA (n = 21), CrCl decreased significantly at 1 month post-OLT (42.6 +/- 26.6 mL/min/1.73 m(2)) when compared with pretransplantation, and 3, 12 and 60 months post-OLT (p < 0.05). It improved between 12 and 60 months post-OLT (p < 0.05). It was correlated with cyclosporine trough levels (p < 0.03), and with total dose of CsA at 12 months. This was not true for patients on tacrolimus (n = 7). Overall pretransplant TRP was below normal (73.7% +/- 19.6), which was significantly lower than the values at years 2, 3, and 5 post-OLT (p < 0.05), owing mainly to the metabolic group which recovered normal proximal tubular function by the end of the second week post-OLT. Calcium/creatinine ratio was significantly worse in the group with liver disease only (p < 0.01). Protein/creatinine ratio normalized rapidly in both groups. Urinary sodium excretion fraction (FENa) was very abnormal in the early postoperative phase, normalizing thereafter in both groups. Kidney function improved after liver transplantation in patients with and without pre-existing kidney dysfunction. Overall, creatinine clearance was correlated to CsA trough levels suggesting CsA did not have an irreversible 'sclerosing' effect in the medium term. Combined antihypertensive therapy using nifedipine and enalapril may be the optimal choice for patients requiring medical management of their hypertension, although the observed effect on creatinine clearance did not reach statistical significance in this study. Tubular dysfunction is frequent in both groups of patients, pre- and post-transplant, and may contribute to bone mineral density as well as to metabolic disturbances in this population.

Genetic Hypercalciuria

Hypercalciuria is an important, identifiable, and reversible risk factor in stone formation. The foremost and most fundamental step in dissecting the genetics of hypercalciuria is understanding its pathophysiology. Hypercalciuria is a complex trait. This article outlines the various factors that compromise the attempt to dissect the genetics of hypercalciuria, summarizes the clinical and experimental monogenic causes of hypercalciuria, and outlines the initial results from attempts in studying polygenic hypercalciuria. Finally, the problem is set in perspective of the current database, technologic advances and limitations are highlighted, and prospects of further advances in the field are speculated upon.

Renal function in tyrosinaemia type I after liver transplantation: a long-term follow-up

Hereditary tyrosinaemia type I is an autosomal recessive inborn error of tyrosine catabolism caused by a deficiency of the enzyme fumarylacetoacetase that results in liver failure, hepatocellular carcinoma, renal tubular dysfunction and acute intermittent porphyria. When treated with liver transplantation, tyrosinaemia type I was considered to be cured. Some years after the first liver transplantations in these patients, some reports focused on the renal function after transplantation. These reports showed that urinary succinylacetone excretion remained but that tubular function normalized. In this report we discuss the long-term renal follow-up (mean follow-up time 11 years, range 7-14 years) after liver transplantation in 9 patients with tyrosinaemia type I treated by liver transplantation in our centre. An evaluation was made of renal function and succinylacetone excretion in urine. In all patients we found a persistent excretion of succinylacetone in the urine. With respect to the glomerular function, we can conclude that there is no clear change in GFR. At the same time, tubulopathy persisted in some patients. We consider that excretion of metabolites such as succinylacetone will be an important contributing factor to tubular dysfunction after liver transplantation in patients with tyrosinaemia type I. Therefore, notwithstanding the major effect of liver transplantation on tyrosine metabolism, renal tubular dysfunction remains at risk and needs careful monitoring. Progressive tubular dysfunction can cause glomerular damage. The use of low-dose NTBC might be considered after liver transplantation in case of tubulopathy to prevent progression of tubular and glomerular dysfunction.

Liquid chromatography–tandem mass spectrometry method for the simultaneous determination of δ-ALA, tyrosine and creatinine in biological fluids

BACKGROUND

Several acquired and congenital human disorders perturb the concentrations of delta-aminolevulinate (delta-ALA), creatinine and tyrosine in biological fluids. There is currently no facile, sensitive and specific method to measure these analytes simultaneously.

METHOD

We developed an LC-MS/MS method to quantify delta-ALA, creatinine and tyrosine in urine that requires minimal sample preparation and no derivatization. The method is also applicable to the analysis of tyrosine in plasma.

RESULTS

All calibration plots were linear, with R(2)>or=0.996. Intra- and interday CVs were <10%. The limit of quantitation for delta-ALA was approximately 0.1 micromol/l, and for creatinine and tyrosine it was well below the lowest measured physiological concentrations. The method was applied to analyze urine from 75 healthy volunteers and 43 patients with hereditary tyrosinemia type I (HT I). The mean urinary concentration of delta-ALA in patients (38+/-35 micromol/l, 53+/-30 mg/g creatinine) was higher than that measured in healthy subjects (5.5+/-2.6 micromol/l, 0.9+/-0.2 mg/g creatinine; p<0.001). Treatment with 2-(2-nitro-4-trifluoromethylbenzyl)-1,3-cyclohexanedione (NTBC), an inhibitor of an early step in tyrosine catabolism, decreased urinary delta-ALA (6.4+/-4.8 micromol/l, 13+/-24 mg/g creatinine; p<0.001). The average plasma tyrosine concentration in healthy volunteers (56+/-14 micromol/l) was within normal reference interval used in clinical practice.

CONCLUSIONS

The method is simple, specific and precise and allows simultaneous quantitation of delta-ALA, creatinine and tyrosine at concentrations present under physiological or pathophysiological conditions.

Renal proximal tubular cells acquire resistance to cell death stimuli in mice with hereditary tyrosinemia type 1

BACKGROUND

Hereditary tyrosinemia type 1 (HT1), which is associated with severe liver and kidney damage, is caused by deficiency of fumarylacetoacetate hydrolase (FAH), the last enzyme of the tyrosine breakdown cascade. HT1-associated liver and kidney failure can be prevented by blocking an enzyme upstream of FAH in the tyrosine breakdown pathway with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC). FAH knockout mice develop the HT1 phenotype when NTBC treatment is discontinued.

METHODS

The occurrence of cell death was investigated in kidneys of Fah(-/-) mice on and off NTBC either unchallenged or injected with 800 mg/kg of homogentisic acid (HGA), an intermediate of tyrosine breakdown.

RESULTS

No cell death could be detected in kidneys of Fah(-/-) mice on NTBC. A slight increase of cleaved caspase-3 was the only apoptosis-related feature that could be detected in kidneys of Fah(-/-) mice off NTBC. Challenge of Fah(-/-) mice on NTBC with HGA led to massive death of renal proximal tubular cells, with positive terminal deoxynucleotidyl transferase-mediated deoxyuridine diphosphate (dUDP) nick-end labeling (TUNEL) and DNA fragmentation assays, but hardly any cleavage of caspase-9 and caspase-3. Fah(-/-) mice off NTBC acquired resistance to HGA-induced renal cell death and the kidneys exhibited relatively few features of apoptosis upon challenge with HGA, with a small increase in expression of cleaved caspase-9 and caspase-3.

CONCLUSION

Kidneys of adult Fah(-/-) mice, withdrawn from NTBC for 15 days, reveal limited characteristics of apoptosis, and have acquired resistance to a caspase-9- and caspase-3-independent form of cell death provoked by HGA.

The effect of long-term calcineurin inhibitor therapy on renal function in children after liver transplantation

Calcineurin inhibitor drugs (CNI), cyclosporin and tacrolimus are potent immunosuppressants, which have improved survival after liver transplantation. We evaluated long-term renal function in children receiving calcineurin inhibitors after liver transplantation. A retrospective analysis of all children undergoing orthotopic liver transplantation (OLT) from 1989 to 1999 who survived 1-yr post-transplantation was performed. All received prednisolone and either cyclosporin and azathioprine or tacrolimus. Steroids were withdrawn at 3 months and cyclosporin/tacrolimus monotherapy was initiated 12 months post-OLT. Calculated glomerular filtration rate (cGFR) was calculated using the modified Counahan-Barratt formula and measured pretransplant, 3, 6 and 12 months post-transplant and annually thereafter. Data were analysed in a serial manner to evaluate the trend of cGFR over time selectively using the Wilcoxon signed rank test and paired t-tests as appropriate. A total of 113 patients (65 males:48 females) were followed up for more than 1 yr (maximum 5 yr). Median (range) age at transplantation was 26 months (3-177). There was a significant fall of 35% in cGFR at 3 months compared with the pretransplant value (p = 0.001). By 12 months following the reduction in immunosuppression dosage, renal function stabilized with a slight improvement in cGFR which reached 76% of the pretransplant value at 5 yr (p < 0.001). Children who were <1 yr of age at the time of OLT had better recovery of renal function than older children (p = 0.02). No association was seen with sex, the type of immunosuppression or the underlying diagnosis. Renal dysfunction is a known complication of CNI therapy. Despite an initial reduction in cGFR, which was associated with maximal immunosuppression, long-term low dose CNI therapy was not associated with continued deterioration of renal function, particularly in children who were transplanted as infants.

Renal function before and long after liver transplantation in children

BACKGROUND

Renal dysfunction occurs in children with liver diseases and renal function is often further impaired after orthotopic liver transplantation (OLT). Inaccurate methods of determining renal function are used in many cases. We studied renal function with accurate methods before and repeatedly after OLT to analyze the effect of the underlying diseases, hypertension, and the immunosuppressive agents.

METHODS

A total of 46 children were studied both before and annually after OLT with clearances of inulin and paraaminohippuric acid to determine the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). The clearance of inulin was also compared with the formula creatinine clearance.

RESULTS

GFR and ERPF decreased from before to after OLT and decreased further during the first years after OLT. Patients with extrahepatic biliary atresia and with tumours showed higher GFR 1 year after OLT than those with metabolic and miscellaneous disorders. No significant change in GFR of individual patients occurred from the first to the last values determined at around 1 and 6 years after OLT. No difference in renal function was seen during the first years between patients treated with cyclosporine as compared to those treated with tacrolimus, but 4 years after OLT, the GFR was higher in the tacrolimus-treated patients. Patients on antihypertensive agents had lower GFR than the normotensive ones. There was no agreement between GFR, determined by clearance of inulin, and that calculated on the basis of serum creatinine and the height of the patients.

CONCLUSIONS

Renal function is reduced by OLT and decreases further during the first years after OLT. Patients with metabolic disorders and those on antihypertensive treatment have the lowest GFR. Determination of GFR by the formula creatinine clearance is inaccurate in children after liver transplantation.

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.

A mouse model of renal tubular injury of tyrosinemia type 1: development of de Toni Fanconi syndrome and apoptosis of renal tubular cells in Fah/Hpd double mutant mice

Hereditary tyrosinemia type 1 (HT1) (McKusick 276700), a severe autosomal recessive disorder of tyrosine metabolism, is caused by mutations in the fumarylacetoacetate hydrolase gene Fah (EC 3.7.1.2), which encodes the last enzyme in the tyrosine catabolic pathway. HT1 is characterized by severe progressive liver disease and renal tubular dysfunction. Homozygous disruption of the gene encoding Fah in mice causes neonatal lethality (e.g., lethal Albino deletion c14CoS mice), an event that limits use of this animal as a model for HT1. A new mouse model was developed with two genetic defects, Fah and 4-hydroxyphenylpyruvate dioxygenase (Hpd). The Fah-/- Hpd-/- mice grew normally without evidence of liver and renal disease, and the phenotype is similar to that in Fah+/+ Hpd-/- mice. The renal tubular cells of Fah-/- Hpd-/- mice, particularly proximal tubular cells, underwent rapid apoptosis when homogentisate, the intermediate metabolite between HPD and FAH, was administered to the Fah-/- Hpd-/- mice. Simultaneously, renal tubular function was impaired and Fanconi syndrome occurred. Apoptotic death of renal tubular cells, but not renal dysfunction, was prevented by pretreatment of the animals with YVAD, a specific inhibitor of caspases. In the homogentisate-treated Fah-/- Hpd-/- mice, massive amounts of succinylacetone were excreted into the urine, regardless of treatment with inhibitors. It is suggested that apoptotic death of renal tubular cells, as induced by administration of homogentisate to Fah-/- Hpd-/- mice, was caused by an intrinsic process, and that renal apoptosis and tubular dysfunctions in tubular cells occurred through different pathways. These observations shed light on the pathogenesis of renal tubular injury in subjects with FAH deficiency. These Fah-/- Hpd-/- mice can serve as a model in experiments related to renal tubular damage.