Effect of nitisinone (NTBC) treatment on the clinical course of hepatorenal tyrosinemia in Québec

In vivo dissection of the mouse tyrosine catabolic pathway with CRISPR-Cas9 identifies modifier genes affecting hereditary tyrosinemia type 1

Hereditary tyrosinemia type 1 is an autosomal recessive disorder caused by mutations (pathogenic variants) in fumarylacetoacetate hydrolase, an enzyme involved in tyrosine degradation. Its loss results in the accumulation of toxic metabolites that mainly affect the liver and kidneys and can lead to severe liver disease and liver cancer. Tyrosinemia type 1 has a global prevalence of approximately 1 in 100,000 births but can reach up to 1 in 1,500 births in some regions of Québec, Canada. Mutating functionally related "modifier' genes (i.e. genes that, when mutated, affect the phenotypic impacts of mutations in other genes) is an emerging strategy for treating human genetic diseases. In vivo somatic genome editing in animal models of these diseases is a powerful means to identify modifier genes and fuel treatment development. In this study, we demonstrate that mutating additional enzymes in the tyrosine catabolic pathway through liver-specific genome editing can relieve or worsen the phenotypic severity of a murine model of tyrosinemia type 1. Neonatal gene delivery using recombinant adeno-associated viral vectors expressing Staphylococcus aureus Cas9 under the control of a liver-specific promoter led to efficient gene disruption and metabolic rewiring of the pathway, with systemic effects that were distinct from the phenotypes observed in whole-body knockout models. Our work illustrates the value of using in vivo genome editing in model organisms to study the direct effects of combining pathological mutations with modifier gene mutations in isogenic settings.

Current status and future directions of liver transplantation for metabolic liver disease in children

Orthotopic liver transplantation (OLT) in the care of children with inborn errors of metabolism (IEM) is well established and represent the second most common indication for pediatric liver transplantation in most centers worldwide, behind biliary atresia. OLT offers cure of disease when a metabolic defect is confined to the liver, but may still be transformative on a patient's quality of life reducing the chance of metabolic crises causing neurological damage in children be with extrahepatic involvement and no "functional cure." Outcomes post-OLT for inborn errors of metabolism are generally excellent. However, this benefit must be balanced with consideration of a composite risk of morbidity, and commitment to a lifetime of post-transplant chronic disease management. An increasing number of transplant referrals for children with IEM has contributed to strain on graft access in many parts of the world. Pragmatic evaluation of IEM referrals is essential, particularly pertinent in cases where progression of extra-hepatic disease is anticipated, with long-term outcome expected to be poor. Decision to proceed with liver transplantation is highly individualized based on the child's dynamic risk-benefit profile, their family unit, and their treating multidisciplinary team. Also to be considered is the chance of future treatments, such as gene therapies, emerging in the medium term.

Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation

Hepatorenal tyrosinemia type 1 (HT-1) is a rare autosomal recessive disease that results from a deficiency of fumaryl acetoacetate hydrolase (FAH), a critical enzyme in the catabolic pathway for tyrosine. This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system. The discovery of 2-[2-nitro-4-trifluoromethylbenzoyl]-1,3-cyclohexanedione (NTBC or nitisinone) has significantly improved the management of HT-1, particularly when initiated before the onset of symptoms. Therefore, newborn screening for HT-1 is essential for timely diagnosis and prompt treatment. The analysis of succinyl acetone (SA) in dried blood spots of newborns followed by quantification of SA in blood or urine for high-risk neonates has excellent sensitivity and specificity for the diagnosis of HT-1. NTBC combined with dietary therapy, if initiated early, can provide liver transplant (LT) free survival and reduce the risk of hepatocellular carcinoma (HCC). Patients failing medical treatment (eg, due to non-adherence), and who develop acute liver failure (ALF), have HCC or evidence of histologically proven dysplastic liver nodule(s), or experience poor quality of life secondary to severe dietary restrictions are currently indicated for LT. Children with HT-1 require frequent monitoring of liver and renal function to assess disease progression and treatment compliance. They are also at risk of long-term neurocognitive impairment, which highlights the need for neurocognitive assessment and therapy.

Structure-based discovery of pyrazole-benzothiadiazole hybrid as human HPPD inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) has attracted increasing attention as a target for treating type I tyrosinemia and other diseases with defects in tyrosine catabolism. Only one commercial drug, 2-(2-nitro-4-trifluoromethylbenzoyl)-1, 3-cyclohexanedione (NTBC), clinically treat type I tyrosinemia, but show some severe side effects in clinical application. Here, we determined the structure of human HPPD-NTBC complex, and developed new pyrazole-benzothiadiazole 2,2-dioxide hybrids from the binding of NTBC. These compounds showed improved inhibition against human HPPD, among which compound a10 was the most active candidate. The Absorption Distribution Metabolism Excretion Toxicity (ADMET) predicted properties suggested that a10 had good druggability, and was with lower toxicity than NTBC. The structure comparison between inhibitor-bound and ligand-free form human HPPD showed a large conformational change of the C-terminal helix. Furthermore, the loop 1 and α7 helix were found adopting different conformations to assist the gating of the cavity, which explains the gating mechanism of human HPPD.

A False-Negative Newborn Screen for Tyrosinemia Type 1-Need for Re-Evaluation of Newborn Screening with Succinylacetone

Undiagnosed and untreated tyrosinemia type 1 (TT1) individuals carry a significant risk for developing liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Elevated succinylacetone (SA) is pathognomonic for TT1 and therefore often used as marker for TT1 newborn screening (NBS). While SA was long considered to be elevated in every TT1 patient, here we present a recent false-negative SA TT1 screen. A nine-year-old boy presented with HCC in a cirrhotic liver. Additional tests for the underlying cause unexpectedly revealed TT1. Nine years prior, the patient was screened for TT1 via SA NBS with a negative result: SA 1.08 µmol/L, NBS cut-off 1.20 µmol/L. To our knowledge, this report is the first to describe a false-negative result from the TT1 NBS using SA. False-negative TT1 NBS results may be caused by milder TT1 variants with lower SA excretion. Such patients are more likely to be missed in NBS programs and can be asymptomatic for years. Based on our case, we advise TT1 to be considered in patients with otherwise unexplained liver pathology, including fibrosis, cirrhosis and HCC, despite a previous negative TT1 NBS status. Moreover, because the NBS SA concentration of this patient fell below the Dutch cut-off value (1.20 µmol/L at that time), as well as below the range of cut-off values used in other countries (1.29-10 µmol/L), it is likely that false-negative screening results for TT1 may also be occurring internationally. This underscores the need to re-evaluate TT1 SA NBS programs.

Clinical and biochemical footprints of inherited metabolic diseases. XIV. Metabolic kidney diseases

Kidney disease is a global health burden with high morbidity and mortality. Causes of kidney disease are numerous, extending from common disease groups like diabetes and arterial hypertension to rare conditions including inherited metabolic diseases (IMDs). Given its unique anatomy and function, the kidney is a target organ in about 10% of known IMDs, emphasizing the relevant contribution of IMDs to kidney disease. The pattern of injury affects all segments of the nephron including glomerular disease, proximal and distal tubular damage, kidney cyst formation, built-up of nephrocalcinosis and stones as well as severe malformations. We revised and updated the list of known metabolic etiologies associated with kidney involvement and found 190 relevant IMDs. This represents the 14th of a series of educational articles providing a comprehensive and revised list of metabolic differential diagnoses according to system involvement.

Hereditary Tyrosinemia Type 1 Mice under Continuous Nitisinone Treatment Display Remnants of an Uncorrected Liver Disease Phenotype

Hereditary tyrosinemia type 1 (HT1) is a genetic disorder of the tyrosine degradation pathway (TIMD) with unmet therapeutic needs. HT1 patients are unable to fully break down the amino acid tyrosine due to a deficient fumarylacetoacetate hydrolase (FAH) enzyme and, therefore, accumulate toxic tyrosine intermediates. If left untreated, they experience hepatic failure with comorbidities involving the renal and neurological system and the development of hepatocellular carcinoma (HCC). Nitisinone (NTBC), a potent inhibitor of the 4-hydroxyphenylpyruvate dioxygenase (HPD) enzyme, rescues HT1 patients from severe illness and death. However, despite its demonstrated benefits, HT1 patients under continuous NTBC therapy are at risk to develop HCC and adverse reactions in the eye, blood and lymphatic system, the mechanism of which is poorly understood. Moreover, NTBC does not restore the enzymatic defects inflicted by the disease nor does it cure HT1. Here, the changes in molecular pathways associated to the development and progression of HT1-driven liver disease that remains uncorrected under NTBC therapy were investigated using whole transcriptome analyses on the livers of Fah- and Hgd-deficient mice under continuous NTBC therapy and after seven days of NTBC therapy discontinuation. Alkaptonuria (AKU) was used as a tyrosine-inherited metabolic disorder reference disease with non-hepatic manifestations. The differentially expressed genes were enriched in toxicological gene classes related to liver disease, liver damage, liver regeneration and liver cancer, in particular HCC. Most importantly, a set of 25 genes related to liver disease and HCC development was identified that was differentially regulated in HT1 vs. AKU mouse livers under NTBC therapy. Some of those were further modulated upon NTBC therapy discontinuation in HT1 but not in AKU livers. Altogether, our data indicate that NTBC therapy does not completely resolves HT1-driven liver disease and supports the sustained risk to develop HCC over time as different HCC markers, including Moxd1, Saa, Mt, Dbp and Cxcl1, were significantly increased under NTBC.

Identification and functional characterization of a novel homozygous intronic variant in the fumarylacetoacetate hydrolase gene in a Chinese patient with tyrosinemia type 1

BACKGROUND

Hereditary tyrosinemia type 1 (HT1; OMIM# 276700) is a genetic metabolism disorder caused by disease-causing variants in the fumarylacetoacetate hydrolase (FAH) gene encoding the last enzyme of the tyrosine catabolic pathway. Herein, we describe the clinical features and genetic characteristics of HT1 in a five years and seven months old Chinese patient.

METHODS

After clinical diagnosis of the proband with HT1, genetic testing was performed by Sanger sequencing of the FAH gene in all family members. Functional analysis of the disease-causing variant was performed by cDNA sequencing to understand the effect of the variant on FAH transcript. To further predict the variant effect, we used Human Splicing Finder (HSF) and PyMol in silico analysis.

RESULTS

We identified a novel previously undescribed intronic variant in the FAH gene (c.914-1G>A). It was detected in a child who was homozygous for the variant and had the clinical presentation of HT1. cDNA sequencing showed that this splice-junction variant affected the transcription of FAH by formation of two different transcripts. Our observations and laboratory experiments were in line with in silico methods.

CONCLUSIONS

Our study provides new insight into the HT1 variant spectrum and a better understanding of this disease in the Chinese population. This will be useful for molecular diagnosis in our country in cases where premarital screening, prenatal diagnosis and preimplantation genetic diagnosis are planned.

Hepatocellular carcinoma requiring liver transplantation in hereditary tyrosinemia type 1 despite nitisinone therapy and α1-fetoprotein normalization

BACKGROUND

Hereditary tyrosinemia type 1 is a rare metabolic condition associated with an increased risk of hepatocellular carcinoma. Nitisinone (2-[2-nitro-4-trifluoromethylbenzoyl]-1,3-cyclohexanedione, NTBC) treatment has reduced but not eliminated the risk. The delayed initiation of nitisinone treatment, and persistently abnormal α1-fetoprotein (AFP) levels are recognized to be risk factors for late-onset hepatocellular carcinoma. We report three children diagnosed and treated with nitisinone since infancy who developed hepatocellular carcinoma despite long-term normalization of AFP.

METHODS

A retrospective review of all patients with tyrosinemia on nitisinone managed at our center was undertaken. Patient demographics, age at diagnosis, duration of therapy, timing of AFP normalization, and radiographic imaging findings were noted.

RESULTS

Three patients at our center with tyrosinemia type 1 developed hepatocellular carcinoma 9-13 years after diagnosis despite long-term nitisinone therapy and normalization of AFP. Two patients developed new nodules on imaging with an elevation of AFP leading to the diagnosis and subsequent liver transplant. The third patient proceeded with liver transplant because of a very nodular liver and increasing splenomegaly despite normal AFP and no change in surveillance gadoxetate magnetic resonance imaging. Early hepatocellular carcinoma was found in her liver explant. All three patients were cirrhotic at diagnosis.

CONCLUSIONS

Patients with hereditary tyrosinemia type 1, especially those already cirrhotic at diagnosis, remain at high risk of developing hepatocellular carcinoma despite long-term nitisinone therapy and AFP normalization, and warrant close monitoring and surveillance.

Neurocognitive outcome and mental health in children with tyrosinemia type 1 and phenylketonuria: A comparison between two genetic disorders affecting the same metabolic pathway

Tyrosinemia type 1 (TT1) and phenylketonuria (PKU) are both inborn errors of phenylalanine-tyrosine metabolism. Neurocognitive and behavioral outcomes have always featured in PKU research but received less attention in TT1 research. This study aimed to investigate and compare neurocognitive, behavioral, and social outcomes of treated TT1 and PKU patients. We included 33 TT1 patients (mean age 11.24 years; 16 male), 31 PKU patients (mean age 10.84; 14 male), and 58 age- and gender-matched healthy controls (mean age 10.82 years; 29 male). IQ (Wechsler-subtests), executive functioning (the Behavioral Rating Inventory of Executive Functioning), mental health (the Achenbach-scales), and social functioning (the Social Skills Rating System) were assessed. Results of TT1 patients, PKU patients, and healthy controls were compared using Kruskal-Wallis tests with post-hoc Mann-Whitney U tests. TT1 patients showed a lower IQ and poorer executive functioning, mental health, and social functioning compared to healthy controls and PKU patients. PKU patients did not differ from healthy controls regarding these outcome measures. Relatively poor outcomes for TT1 patients were particularly evident for verbal IQ, BRIEF dimensions "working memory", "plan and organize" and "monitor", ASEBA dimensions "social problems" and "attention problems", and for the SSRS "assertiveness" scale (all p values <0.001). To conclude, TT1 patients showed cognitive impairments on all domains studied, and appeared to be significantly more affected than PKU patients. More attention should be paid to investigating and monitoring neurocognitive outcome in TT1 and research should focus on explaining the underlying pathophysiological mechanism.

Biochemical and behavioural profile of NTBC treated Tyrosinemie type 1 mice

BACKGROUND

Tyrosinemia type 1 (HT1) is a rare metabolic disorder caused by a defect in the tyrosine catabolic pathway. Since HT1 patients are treated with NTBC, outcome improved and life expectancy greatly increased. However extensive neurocognitive and behavioural problems have been described, which might be related to treatment with NTBC, the biochemical changes induced by NTBC, or metabolites accumulating due to the enzymatic defect characterizing the disease.

OBJECTIVE

To study the possible pathophysiological mechanisms of brain dysfunction in HT1, we assessed blood and brain LNAA, and brain monoamine neurotransmitter metabolite levels in relation to behavioural and cognitive performance of HT1 mice.

DESIGN

C57BL/6 littermates were divided in three different experimental groups: HT1, heterozygous and wild-type mice (n = 10; 5 male). All groups were treated with NTBC and underwent cognitive and behavioural testing. One week after behavioural testing, blood and brain material were collected to measure amino acid profiles and brain monoaminergic neurotransmitter levels.

RESULTS

Irrespective of the genetic background, NTBC treatment resulted in a clear increase in brain tyrosine levels, whereas all other brain LNAA levels tended to be lower than their reference values. Despite these changes in blood and brain biochemistry, no significant differences in brain monoamine neurotransmitter (metabolites) were found and all mice showed normal behaviour and learning and memory.

CONCLUSION

Despite the biochemical changes, NTBC and genotype of the mice were not associated with poorer behavioural and cognitive function of the mice. Further research involving dietary treatment of FAH-/- are warranted to investigate whether this reveals the cognitive impairments that have been seen in treated HT1 patients.

Pharmacophore-Oriented Discovery of Novel 1,2,3-Benzotriazine-4-one Derivatives as Potent 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a functional protein existing in almost all aerobic organisms. In the field of agricultural chemicals, HPPD is acknowledged to be one of the crucial targets for herbicides at present due to its unique bio-function in plants. In the Auto Core Fragment in silico Screening (ACFIS) web server, a potential HPPD inhibitor featuring 1,2,3-benzotriazine-4-one was screened out via a pharmacophore-linked fragment virtual screening (PFVS) method. Molecular simulation studies drove the process of "hit-to-lead" optimization, and a family of 1,2,3-benzotriazine-4-one derivatives was synthesized. Consequently, 6-(2-hydroxy-6-oxocyclohex-1-ene-1-carbonyl)-5-methyl-3-(2-methylbenzyl)benzo[d][1,2,3]triazin-4(3H)-one (15bu) was identified to be the best HPPD inhibitor (IC₅₀ = 36 nM) among the 1,2,3-benzotriazine-4-one derivatives, which had over 8-fold improvement of enzyme inhibition compared with the positive control mesotrione (IC₅₀ = 289 nM). Crystallography information for the AtHPPD-15bu complex revealed several important interactions of the ligand bound upon the target protein, i.e., the bidentate chelating interaction of the triketone motif with the metal ion of AtHPPD, a tight π-π stacking interaction consisting of the1,2,3-benzotriazine-4-one moiety and two benzene rings of Phe-424 and Phe-381, and the polydirectional hydrophobic contacts consisting of the ortho-CH₃-benzyl group of the core scaffold and some hydrophobic residues. Furthermore, compound 15bu displayed 100% inhibition against the five species of target weeds at the tested dosage, which was comparable to the weed control of mesotrione. Collectively, the fused 1,2,3-benzotriazine-4-one-triketone hybrid is a promising chemical tool for the development of more potent HPPD inhibitors and provides a valuable lead compound 15bu for herbicide innovation.

Clinical experience with hepatorenal tyrosinemia from a single Egyptian center

Although very recently, in Egypt, sick newborn screening has included screening for hepatorenal tyrosinemia, yet, it is not yet included in nationwide neonatal screening and hence diagnosis may be delayed. The aim of this study was to analyze data of all cases presenting with hepatorenal tyrosinemia to the Pediatric Hepatology Unit, Cairo University, Egypt from 2006 to 2019. Data were retrieved from patients’ files including age of onset of symptoms, clinical signs, blood counts, liver functions, serum phosphorous, alpha-fetoprotein, succinylacetone and abdominal ultrasound. During this period, 76 patients were diagnosed with hepatorenal tyrosinemia if succinylacetone in dry blood spot was elevated above 1 μmol/L. These 76 cases came from 70 families; consanguinity was reported in 61 families. In our cohort we reported 30 affected siblings with a similar clinical presentation, who died undiagnosed. Presentation was acute in 26%, subacute in 30% and chronic in 43%. Abdominal distention was the commonest presenting symptom (52.6%). Coagulopathy was the commonest derangement in liver functions; hyperbilirubinemia and raised transaminases were less common. Ultrasound findings included hepatic focal lesions in 47% and enlarged echogenic kidneys in 39% and 45.3% respectively. Only 20 children were treated with Nitisinone because of unavailability and high costs; seven out of them underwent liver transplantation. In conclusion, although hepatorenal tyrosinemia is a rare inborn error of metabolism, in a large population country with high rate of consanguinity; this disease is not uncommonly diagnosed. The current treatment is not readily available because of the costs in a resource-limited country. Neonatal screening and subsidization of the costly medication need to be considered.

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.

Clinical and genetic characteristics of two patients with tyrosinemia type 1 in Slovenia – A novel fumarylacetoacetate hydrolase (FAH) intronic disease-causing variant

Tyrosinemia type 1 (HT1) is an inborn error of tyrosine catabolism that leads to severe liver, kidney, and neurological dysfunction. Newborn screening (NBS) can enable a timely diagnosis and early initiation of treatment.

We presented the follow up of the only two Slovenian patients diagnosed with HT1. Metabolic control was monitored by measuring tyrosine, phenylalanine and succinylacetone from dried blood spots (DBSs). Retrograde screening of HT1 was performed from DBSs taken at birth using tandem mass spectrometry.

First patient was diagnosed at the age of 6 months in the asymptomatic phase due to an abnormal liver echogenicity, the other presented at 2.5 months with an acute liver failure and needed a liver transplantation. The first was a compound heterozygote for a novel FAH intronic variant c.607-21A>G and c.192G>T whereas the second was homozygous for c.192G>T. At the non-transplanted patient, 66% of tyrosine and 79% of phenylalanine measurements were in strict reference ranges of 200–400 μmol/L and >30 μmol/L, respectively, which resulted in a favorable cognitive outcome at 3.6 years. On retrograde screening, both patients had elevated SA levels; on the other hand, tyrosine was elevated only at one.

We showed that non-coding regions should be analyzed when clinical and biochemical markers are characteristic of HT1. DBSs represent a convenient sample type for frequent amino acid monitoring. Retrograde diagnosis of HT1 was possible after more than three years of birth with SA as a primary marker, complemented by tyrosine.

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Non-coding region variants of FAH gene can result in a symptomatic HT1.

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Retrograde screening for HT1 is technically possible even three years after birth.

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DBS are convenient for monitoring HT1 patients and are family-friendly.

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Regular monitoring in HT1 patients can result in a favorable cognitive outcome.

Hereditary Tyrosinemia Type 1 in Jordan: A Retrospective Study

Background

Hereditary tyrosinemia type 1 (HT1) is a recessively inherited inborn error of metabolism affecting the final step of tyrosine catabolism. The accumulation of tyrosine toxic metabolites leads to progressive hepatic, renal, and neurological manifestations. Treatment of HT1 consists of tyrosine-restricted diets and nitisinone. The untreated disease progresses into life-threatening liver failure with an increased risk of hepatocellular carcinoma.

Methods

From April 2010 to March 2021, eighteen patients were diagnosed with HT1 in the metabolic department at Queen Rania Al Abdullah Hospital for Children in Jordan. Patients were reviewed retrospectively regarding their clinical features, laboratory data, and sociodemographic history.

Results

The mean age of nine boys and nine girls was 6.03 years (SD ± 3.85). The mean age for symptom onset was 5.61 months (SD ± 6.02). However, the diagnosis was belated from the onset by 10.50 months (±10.42). Nitisinone treatment was delayed from diagnosis around 12.28 months (SD ± 25.36). Most of the patients (66.7%) had acute onset of the disease. Two children (11.1%) died due to hepatic complications. Positive family history was identified in 61.1% of patients, and a similar percentage were born to parents with consanguineous marriage. The most common presentation was abdominal pain, vomiting, and fever. Hepatomegaly and abdominal distention were the most common findings. Six patients' (42.9%) first presentation was rickets.

Conclusion

HT1 diagnosis is usually delayed because it is not part of newborn screening and nonfamiliarity with the clinical features of the disease. Therefore, nationwide newborn screening should be expanded to include HT1.

NTBC Treatment Monitoring in Chilean Patients with Tyrosinemia Type 1 and Its Association with Biochemical Parameters and Liver Biomarkers

Treatment and follow-up in Hereditary Tyrosinemia type 1 (HT-1) patients require comprehensive clinical and dietary management, which involves drug therapy with NTBC and the laboratory monitoring of parameters, including NTBC levels, succinylacetone (SA), amino acids, and various biomarkers of liver and kidney function. Good adherence to treatment and optimal adjustment of the NTBC dose, according to clinical manifestations and laboratory parameters, can prevent severe liver complications such as hepatocarcinogenesis (HCC). We analyzed several laboratory parameters for 15 HT-1 patients over one year of follow-up in a cohort that included long-term NTBC-treated patients (more than 20 years), as well as short-term patients (one year). Based on this analysis, we described the overall adherence by our cohort of 70% adherence to drug and dietary treatment. A positive correlation was found between blood and plasma NTBC concentration with a conversion factor of 2.57. Nonetheless, there was no correlation of the NTBC level with SA levels, αFP, liver biomarkers, and amino acids in paired samples analysis. By separating according to the range of the NTBC concentration, we therefore determined the mean concentration of each biochemical marker, for NTBC ranges above 15–25 μmol/L. SA in urine and αFP showed mean levels within controlled parameters in our group of patients. Future studies analyzing a longer follow-up period, as well as SA determination in the blood, are encouraged to confirm the present findings.

Liver tumors in children with chronic liver diseases

Liver tumors are rare in children, but the incidence may increase in some circumstances and particularly in chronic liver diseases. Most liver tumors consequent to chronic liver diseases are malignant hepatocellular carcinoma. Other liver tumors include hepatoblastoma, focal nodular hyperplasia, adenoma, pseudotumor, and nodular regenerative hyperplasia. Screening of suspected cases is beneficial. Imaging and surrogate markers of alpha-fetoprotein are used initially as noninvasive tools for surveillance. However, liver biopsy for histopathology evaluation might be necessary for patients with inconclusive findings. Once the malignant liver tumor is detected in children with cirrhosis, liver transplantation is currently considered the preferred option and achieves favorable outcomes. Based on the current evidence, this review focuses on liver tumors with underlying chronic liver disease, their epidemiology, pathogenesis, early recognition, and effective management.

β-Cyclodextrin Derivative Grafted on Silica Gel Represents a New Polymeric Sorbent for Extracting Nitisinone from Model Physiological Fluids

Nitisinone (NTBC) is used in the treatment of disorders affecting the tyrosine pathway, including hereditary tyrosinemia type I, alkaptonuria, and neuroblastoma. An inappropriate dosage of this therapeutic drug causes side effects; therefore, it is necessary to develop a rapid and sensitive method to monitor the content of NTBC in patients' blood. This study aimed to develop anew polymeric sorbent containing β-cyclodextrin (β-CD) derivatives grafted on silica gel to effectively extract NTBC from model physiological fluids. The inclusion complex formed between β-CD and NTBC was examined by proton nuclear magnetic resonance spectroscopy. The novel sorbents with derivatives of β-CD were prepared on modified silica gel using styrene as a comonomer, ethylene glycol dimethacrylate as a crosslinking agent, and 2,2'-azo-bis-isobutyronitrile as a polymerization initiator. The obtained products were characterized via Fourier transform infrared spectroscopy and then used as sorbents as part of a solid phase extraction technique. High NTBC recovery (70%indicated that the developed polymeric sorbent may be suitable for extracting this compound from patients' blood samples.

Long-term safety and outcomes in hereditary tyrosinaemia type 1 with nitisinone treatment: a 15-year non-interventional, multicentre study

BACKGROUND

Since the EU approval of nitisinone in 2005, prognosis for patients with hereditary tyrosinaemia type 1 has changed dramatically, with patients living with the disease now reaching adulthood for the first time in history. This study aimed to assess the long-term safety and outcomes of nitisinone treatment in patients with hereditary tyrosinaemia type 1.

METHODS

We did a non-interventional, non-comparative, multicentre study in 77 sites across 17 countries in Europe and collected retrospective and prospective longitudinal data in patients with hereditary tyrosinaemia type 1 who were treated with oral nitisinone during the study period (Feb 21, 2005, to Sept 30, 2019). There were no specific exclusion criteria. Patients were followed-up with an investigator at least annually for as long as they were treated, or until the end of the study. The primary endpoints, occurrence of adverse events related to hepatic, renal, ophthalmic, haematological, or cognitive or developmental function, were assessed in the complete set (all patients already receiving treatment at the index date [Feb 21, 2005] or starting treatment thereafter) and the index set (the subset of patients who had their first dose on the index date or later only).

FINDINGS

315 patients were enrolled during the study period (complete set). Additionally, data from 24 patients who had liver transplantation or died during the post-marketing surveillance programme were retrieved (extended analysis set; 339 patients). Median treatment duration was 11·2 years (range 0·7-28·4); cumulative nitisinone exposure was 3172·7 patient-years. Patients who were diagnosed by neonatal screening started nitisinone treatment at median age 0·8 months versus 8·5 months in those who presented clinically. Incidences of hepatic, renal, ophthalmic, haematological, or cognitive or developmental adverse events were low. Occurrence of liver transplantation or death was more frequent the later that treatment was initiated (none of 70 patients who started treatment at age <28 days vs 35 [13%] of 268 patients who started treatment at age ≥28 days). 279 (89%) of 315 patients were assessed as having either very good or good nitisinone treatment compliance. Treatment and diet compliance declined as patients aged. Suboptimal plasma phenylalanine and tyrosine levels were observed. The majority of patients were reported to have good overall clinical condition throughout treatment; 176 (87%) of 203 during the entire study, 98% following 1 year of treatment.

INTERPRETATION

Long-term nitisinone treatment was well tolerated and no new safety signals were revealed. Life-limiting hepatic disease appears to have been prevented by early treatment start. Neonatal screening was the most effective way of ensuring early treatment. Standardised monitoring of blood tyrosine, phenylalanine, and nitisinone levels has potential to guide individualised therapy.

FUNDING

Swedish Orphan Biovitrum (Sobi).

Pediatric metabolic liver diseases: Evolving role of liver transplantation

Metabolic liver diseases (MLD) are the second most common indication for liver transplantation (LT) in children. This is based on the fact that the majority of enzymes involved in various metabolic pathways are present within the liver and LT can cure or at least control the disease manifestation. LT is also performed in metabolic disorders for end-stage liver disease, its sequelae including hepatocellular cancer. It is also performed for preventing metabolic crisis’, arresting progression of neurological dysfunction with a potential to reverse symptoms in some cases and for preventing damage to end organs like kidneys as in the case of primary hyperoxalosis and methyl malonic acidemia. Pathological findings in explant liver with patients with metabolic disease include unremarkable liver to steatosis, cholestasis, inflammation, variable amount of fibrosis, and cirrhosis. The outcome of LT in metabolic disorders is excellent except for patients with mitochondrial disorders where significant extrahepatic involvement leads to poor outcomes and hence considered a contraindication for LT. A major advantage of LT is that in the post-operative period most patients can discontinue the special formula which they were having prior to the transplant and this increases their well-being and improves growth parameters. Auxiliary partial orthotopic LT has been described for patients with noncirrhotic MLD where a segmental graft is implanted in an orthotopic position after partial resection of the native liver. The retained native liver can be the potential target for future gene therapy when it becomes a clinical reality.

Pediatric Hepatocellular Carcinoma

PURPOSE

Pediatric hepatocellular carcinoma is rarely seen in childhood. It constitutes approximately 1% of childhood solid organ malignancies. Pediatric hepatocellular carcinoma is the second most common malignant liver tumor after hepatoblastoma in children. In this review, we aimed to review the diagnosis and treatment of pediatric hepatocellular carcinoma in the light of the latest literature.

METHODS

We reviewed the literature in terms of the diagnosis and treatment of pediatric hepatocellular carcinoma.

RESULTS

Hepatocellular carcinoma (HCC) and hepatoblastoma constitute 0.5-1.5% of all childhood malignant tumors. HCC is responsible for 27% of all liver tumors and 4% of all pediatric liver transplantations. While 99.6% of HCC is seen in adults, only 0.4% of it is seen in pediatric patients. Etiological predisposition and biological behavior are different from adults. In a child with cirrhosis or liver disease, HCC should be suspected in the presence of a high level of AFP and an abnormal nodule on ultrasonography. Hepatoblastoma should be considered first in the differential diagnosis.

CONCLUSION

Treatment of pediatric HCC is challenging. Complete surgical resection is essential for the cure. To this end, different neoadjuvant chemotherapy protocols have been designed to convert non-resectable tumors into resectable tumors. For tumors that cannot be resected, liver transplantation for each patient with childhood HCC should be decided individually.

EU FP7 research funding for an orphan drug (Orfadin®) and vaccine (Hep C) development: a success and a failure?

BACKGROUND

We considered the extent of the contribution of publicly funded research to the late-stage clinical development of pharmaceuticals and medicinal products, based on the European Commission (EC) FP7 research funding programme. Using two EC FP7-HEALTH case study examples-representing two types of outcomes-we then estimated wider public and charitable research funding contributions.

METHODS

Using the publicly available database of FP7-HEALTH funded projects, we identified awards relating to late-stage clinical development according to the systematic application of inclusion and exclusion criteria, classified them according to product type and clinical indication, and calculated total EC funding amounts. We then identified two case studies representing extreme outcomes: failure to proceed with the product (hepatitis C vaccine) and successful market authorisation (Orfadin® for alkaptonuria). Total public and philanthropic research funding contributions to these products were then estimated using publicly available information on funding.

RESULTS

12.3% (120/977) of all EC FP7-HEALTH awards related to the funding of late-stage clinical research, totalling € 686,871,399. Pharmaceutical products and vaccines together accounted for 84% of these late-stage clinical development research awards and 70% of its funding. The hepatitis C vaccine received total European Community (FP7 and its predecessor, EC Framework VI) funding of €13,183,813; total public and charitable research funding for this product development was estimated at € 77,060,102. The industry sponsor does not consider further development of this product viable; this now represents public risk investment. FP7 funding for the late-stage development of Orfadin® for alkaptonuria was so important that the trials it funded formed the basis for market authorisation, but it is not clear whether the price of the treatment (over €20,000 per patient per year) adequately reflects the substantial public funding contribution.

CONCLUSIONS

Public and charitable research funding plays an essential role, not just in early stage basic research, but also in the late-stage clinical development of products prior to market authorisation. In addition, it provides risk capital for failed products. Within this context, we consider further discussions about a public return on investment and its reflection in pricing policies and decisions justified.

Oxidative Stress, Glutathione Metabolism, and Liver Regeneration Pathways Are Activated in Hereditary Tyrosinemia Type 1 Mice upon Short-Term Nitisinone Discontinuation

Hereditary tyrosinemia type 1 (HT1) is an inherited condition in which the body is unable to break down the amino acid tyrosine due to mutations in the fumarylacetoacetate hydrolase (FAH) gene, coding for the final enzyme of the tyrosine degradation pathway. As a consequence, HT1 patients accumulate toxic tyrosine derivatives causing severe liver damage. Since its introduction, the drug nitisinone (NTBC) has offered a life-saving treatment that inhibits the upstream enzyme 4-hydroxyphenylpyruvate dioxygenase (HPD), thereby preventing production of downstream toxic metabolites. However, HT1 patients under NTBC therapy remain unable to degrade tyrosine. To control the disease and side-effects of the drug, HT1 patients need to take NTBC as an adjunct to a lifelong tyrosine and phenylalanine restricted diet. As a consequence of this strict therapeutic regime, drug compliance issues can arise with significant influence on patient health. In this study, we investigated the molecular impact of short-term NTBC therapy discontinuation on liver tissue of Fah-deficient mice. We found that after seven days of NTBC withdrawal, molecular pathways related to oxidative stress, glutathione metabolism, and liver regeneration were mostly affected. More specifically, NRF2-mediated oxidative stress response and several toxicological gene classes related to reactive oxygen species metabolism were significantly modulated. We observed that the expression of several key glutathione metabolism related genes including Slc7a11 and Ggt1 was highly increased after short-term NTBC therapy deprivation. This stress response was associated with the transcriptional activation of several markers of liver progenitor cells including Atf3, Cyr61, Ddr1, Epcam, Elovl7, and Glis3, indicating a concreted activation of liver regeneration early after NTBC withdrawal.

Type 1 tyrosinemia in Finland: a nationwide study

Background

Introduction of nitisinone and newborn screening (NBS) have transformed the treatment of type 1 tyrosinemia, but the effects of these changes on the long-term outcomes remain obscure. Also, the predictors for later complications, the significance of drug levels and the normalization of laboratory and imaging findings are poorly known. We investigated these issues in a nationwide study.

Results

Type 1 tyrosinemia was diagnosed in 22 children in 1978–2019 in Finland. Incidence was 1/90,102, with a significant enrichment in South Ostrobothnia (1/9990). Median age at diagnosis was 5 (range 0.5–36) months, 55% were girls and 13 had homozygotic Trp262X mutation. Four patients were detected through screening and 18 clinically, their main findings being liver failure (50% vs. 100%, respectively, p = 0.026), ascites (0% vs. 53%, p = 0.104), renal tubulopathy (0% vs. 65%, p = 0.035), rickets (25% vs. 65%, p = 0.272), growth failure (0% vs. 66%, p = 0.029), thrombocytopenia (25% vs. 88%, p = 0.028) and anaemia (0% vs. 47%, p = 0.131). One patient was treated with diet, seven with transplantation and 14 with nitisinone. Three late-diagnosed (6–33 months) nitisinone treated patients needed transplantation later. Kidney dysfunction (86% vs. 7%, p = 0.001), hypertension (57% vs. 7%, p = 0.025) and osteopenia/osteoporosis (71% vs. 14%, p = 0.017) were more frequent in transplanted than nitisinone-treated patients. Blood/serum alpha-fetoprotein decreased rapidly on nitisinone in all but one patient, who later developed intrahepatic hepatocellular carcinoma. Liver values normalized in 31 months and other laboratory values except thrombocytopenia within 18 months. Imaging findings normalized in 3–56 months excluding five patients with liver or splenic abnormalities. Low mean nitisinone concentration was associated with higher risk of severe complications (r = 0.758, p = 0.003) despite undetectable urine succinylacetone.

Conclusions

Prognosis of type 1 tyrosinemia has improved in the era of nitisinone, and NBS seems to provide further benefits. Nevertheless, the long-term risk for complications remains, particularly in the case of late diagnosis and/or insufficient nitisinone levels.

The future of gene-targeted therapy for hereditary tyrosinemia type 1 as a lead indication among the inborn errors of metabolism

Introduction

Inborn errors of metabolism (IEMs) often result from single-gene mutations and collectively cause liver dysfunction in neonates leading to chronic liver and systemic disease. Current treatments for many IEMs are limited to maintenance therapies that may still require orthotropic liver transplantation. Gene therapies offer a potentially superior approach by correcting or replacing defective genes with functional isoforms; however, they face unique challenges from complexities presented by individual diseases and their diverse etiology, presentation, and pathophysiology. Furthermore, immune responses, off-target gene disruption, and tumorigenesis are major concerns that need to be addressed before clinical application of gene therapy.

Areas covered

The current treatments for IEMs are reviewed as well as the advances in, and barriers to, gene therapy for IEMs. Attention is then given to ex vivo and in vivo gene therapy approaches for hereditary tyrosinemia type 1 (HT1). Of all IEMs, HT1 is particularly amenable to gene therapy because of a selective growth advantage conferred to corrected cells, thereby lowering the initial transduction threshold for phenotypic relevance.

Expert opinion

It is proposed that not only is HT1 a safe indication for gene therapy, its unique characteristics position it to be an ideal IEM to develop for clinical investigation.

The Importance of Succinylacetone: Tyrosinemia Type I Presenting with Hyperinsulinism and Multiorgan Failure Following Normal Newborn Screening

Tyrosinemia type 1 (TT1) is an inborn error of tyrosine metabolism with features including liver dysfunction, cirrhosis, and hepatocellular carcinoma; renal dysfunction that may lead to failure to thrive and bone disease; and porphyric crises. Once fatal in most infantile-onset cases, pre-symptomatic diagnosis through newborn screening (NBS) protocols, dietary management, and pharmacotherapy with nitisinone have improved outcomes. Succinylacetone provides a sensitive and specific marker for the detection of TT1 but is not universally utilized in screening protocols for the disease. Here, we report an infant transferred to our facility for evaluation and management of hyperinsulinism who subsequently developed acute-onset liver, respiratory, and renal failure around one month of life. She was found to have TT1 caused by novel pathogenic variant in fumarylacetoacetate hydrolase (c.1014 delC, p.Cys 338 Ter). Her NBS, which utilized tyrosine as a primary marker, had been reported as normal, with a tyrosine level of 151 μmol/L (reference: < 280 μmol/L). Retrospective analysis of dried blood spot samples via tandem mass spectrometry showed detectable succinylacetone ranging 4.65-10.34 μmol/L. To our knowledge, this is the first patient with TT1 whose initial presenting symptom was hyperinsulinemic hypoglycemia. The case highlights the importance of maintaining a high suspicion for metabolic disease in critically ill children, despite normal NBS. We also use the case to advocate for NBS for TT1 using succinylacetone quantitation.

First Scandinavian case of successful pregnancy during nitisinone treatment for type 1 tyrosinemia

Background Type 1 tyrosinemia is a hereditary metabolic disease in which tyrosine metabolites damage the liver and kidneys. Nitisinone medication revolutionized the treatment, but the effects of the drug during human pregnancy are unknown. Case presentation A 17-year-old tyrosinemia patient became pregnant. Nitisinone was continued throughout pregnancy with a varying serum concentration and dose ranging from 0.8 to 1.4 mg/kg/day. Blood tyrosine remained stable until it increased in late pregnancy. α-fetoprotein increased to 284 μg/L without new changes in liver. Urine succinylacetone remained undetectable, but there were signs of possibly reoccurring kidney tubulopathy. Fetal ultrasound monitoring was normal throughout the pregnancy and the newborn healthy. After the delivery, α-fetoprotein normalized, but tyrosine continued to rise for up to 1 year. The child is developing normally. Conclusions Pregnancy during nitisinone was successful, but tailoring of the drug dose and possibly reappearing complications, as also increasing serum tyrosine concentration after delivery warranted intensified surveillance.

Natural Protein Tolerance and Metabolic Control in Patients with Hereditary Tyrosinaemia Type 1

In a longitudinal retrospective study, we aimed to assess natural protein (NP) tolerance and metabolic control in a cohort of 20 Hereditary Tyrosinaemia type I (HTI) patients. Their median age was 12 years ([3.2-17.7 years], n = 11 female, n = 8 Caucasian, n = 8 Asian origin, n = 2 Arabic and n = 2 Indian). All were on nitisinone (NTBC) with a median dose of 0.7 g/kg/day (range 0.4-1.5 g/kg/day) and were prescribed a tyrosine (Tyr)/phenylalanine (Phe)-restricted diet supplemented with Tyr/Phe-free L-amino acids. Data were collected on clinical signs at presentation, medical history, annual dietary prescriptions, and blood Phe and Tyr levels from diagnosis until transition to the adult service (aged 16-18 years) or liver transplantation (if it preceded transition). The median age of diagnosis was 2 months (range: 0 to 24 months), with n = 1 diagnosed by newborn screening, n = 3 following phenylketonuria (PKU) screening and n = 7 by sibling screening. Five patients were transplanted (median age 6.3 years), and one died due to liver cancer. The median follow-up was 10 years (3-16 years), and daily prescribed NP intake increased from a median of 5 to 24 g/day. Lifetime median blood Tyr (370 µmol/L, range 280-420 µmol/L) and Phe (50 µmol/L, 45-70 µmol/L) were maintained within the target recommended ranges. This cohort of HTI patients were able to increase the daily NP intake with age while maintaining good metabolic control. Extra NP may improve lifelong adherence to the diet.

Combined 3D-quantitative structure-activity relationships and topomer technology-based molecular design of human 4-hydroxyphenylpyruvate dioxygenase inhibitors

Aim: 4-Hydroxyphenylpyruvate dioxygenase (HPPD) has attracted increasing attention as an important target against tyrosinemia type I. This paper aimed to explore the structure-activity relationship of HPPD inhibitors with pyrazole scaffolds and to design novel HPPD inhibitors. Methodology & results: The best 3D-quantitative structure-activity relationships model was established by two different strategies based on 40 pyrazole scaffold-based analogs. Screening of molecular fragments by topomer technology, combined with molecular docking, 14 structures were identified for potential human HPPD inhibitory activity. Molecular dynamics results demonstrated that all the compounds obtained bound to the enzyme and possessed a satisfactory binding free energy. Conclusion: The quantitative structure-activity relationship of HPPD inhibitors of pyrazole scaffolds was clarified and 14 original structures with potential human HPPD inhibitory activity were obtained.

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.

Emotional and behavioral problems, quality of life and metabolic control in NTBC-treated Tyrosinemia type 1 patients

Abstract

Background

Treatment with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) and dietary phenylalanine and tyrosine restriction improves physical health and life expectancy in Tyrosinemia type 1 (TT1). However, neurocognitive outcome is suboptimal. This study aimed to investigate behavior problems and health-related quality of life (HR-QoL) in NTBC-dietary-treated TT1 and to relate this to phenylalanine and tyrosine concentrations.

Results

Thirty-one TT1 patients (19 males; mean age 13.9 ± 5.3 years) were included in this study. Emotional and behavioral problems, as measured by the Achenbach System of Empirically Based Assessment, were present in almost all domains. Attention and thought problems were particularly evident. HR-QoL was assessed by the TNO AZL Children’s and Adults QoL questionnaires. Poorer HR-QoL as compared to reference populations was observed for the domains: independent daily functioning, cognitive functioning and school performance, social contacts, motor functioning, and vitality. Both internalizing and externalizing behavior problems were associated with low phenylalanine (and associated lower tyrosine) concentrations during the first year of life. In contrast, high tyrosine (and associated higher phenylalanine) concentrations during life and specifically the last year before testing were associated with more internalizing behavior and/or HR-QoL problems.

Conclusions

TT1 patients showed several behavior problems and a lower HR-QoL. Associations with metabolic control differed for different age periods. This suggests the need for continuous fine-tuning and monitoring of dietary treatment to keep phenylalanine and tyrosine concentrations within target ranges in NTBC-treated TT1 patients.

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.

The Effect of Various Doses of Phenylalanine Supplementation on Blood Phenylalanine and Tyrosine Concentrations in Tyrosinemia Type 1 Patients

Tyrosinemia type 1 (TT1) treatment with 2-(2-nitro-4-trifluormethyl-benzyl)-1,3-cyclohexanedione (NTBC) and a phenylalanine-tyrosine restricted diet is associated with low phenylalanine concentrations. Phenylalanine supplementation is prescribed without comprehensive consideration about its effect on metabolic control. We investigated the effect of phenylalanine supplementation on bloodspot phenylalanine, tyrosine, NTBC and succinylacetone. Eleven TT1 patients received 0, 20 and 40 mg/kg/day phenylalanine supplementation with the phenylalanine-tyrosine free L-amino acid supplements. Bloodspots were collected before breakfast, midday and evening meal. Differences between study periods, sample times and days within a study period were studied using (generalized) linear mixed model analyses. Twenty and 40 mg/kg/day phenylalanine supplementation prevented daytime phenylalanine decreases (p = 0.05) and most low phenylalanine concentrations, while tyrosine concentrations increased (p < 0.001). Furthermore, NTBC and succinylacetone concentrations did not differ between study periods. To conclude, 20 mg/kg/day phenylalanine supplementation can prevent most low phenylalanine concentrations without increasing tyrosine to concentrations above the target range or influencing NTBC and succinylacetone concentrations, while 40 mg/kg/day increased tyrosine concentrations to values above the targeted range. Additionally, this study showed that the effect of phenylalanine supplementation, and a possible phenylalanine deficiency, should be assessed using pre-midday meal blood samples that could be combined with an overnight fasted sample when in doubt.

Evolution of tyrosinemia type 1 disease in patients treated with nitisinone in Spain

Treatment with nitisinone (NTBC) has brought about a drastic improvement in the treatment and prognosis of hereditary tyrosinemia type I (HT1). We conducted a retrospective observational multicentric study in Spanish HT1 patients treated with NTBC to assess clinical and biochemical long-term evolution.We evaluated 52 patients, 7 adults and 45 children, treated with NTBC considering: age at diagnosis, diagnosis by clinical symptoms, or by newborn screening (NBS); phenotype (acute/subacute/chronic), mutational analysis; symptoms at diagnosis and clinical course; biochemical markers; doses of NTBC; treatment adherence; anthropometric evolution; and neurocognitive outcome.The average follow-up period was 6.1 ± 4.9 and 10.6 ± 5.4 years in patients with early and late diagnosis respectively. All patients received NTBC from diagnosis with an average dose of 0.82 mg/kg/d. All NBS-patients (n = 8) were asymptomatic at diagnosis except 1 case with acute liver failure, and all remain free of liver and renal disease in follow-up. Liver and renal affectation was markedly more frequent at diagnosis in patients with late diagnosis (P < .001 and .03, respectively), with ulterior positive hepatic and renal course in 86.4% and 93.2% of no-NBS patients, although 1 patient with good metabolic control developed hepatocarcinoma.Despite a satisfactory global nutritional evolution, 46.1% of patients showed overweight/obesity. Interestingly lower body mass index was observed in patients with good dietary adherence (20.40 ± 4.43 vs 24.30 ± 6.10; P = .08) and those with good pharmacological adherence (21.19 ± 4.68 vs 28.58 ± 213.79).intellectual quotient was ≥85 in all NBS- and 68.75% of late diagnosis cases evaluated, 15% of which need pedagogical support, and 6.8% (3/44) showed school failure.Among the 12 variants identified in fumarylacetoacetate hydrolase gene, 1 of them novel (H63D), the most prevalent in Spanish population is c.554-1 G>T.After NTBC treatment a reduction in tyrosine and alpha-fetoprotein levels was observed in all the study groups, significant for alpha-fetoprotein in no NBS-group (P = .03), especially in subacute/chronic forms (P = .018).This series confirms that NTBC treatment had clearly improved the prognosis and quality of life of HT1 patients, but it also shows frequent cognitive dysfunctions and learning difficulties in medium-term follow-up, and, in a novel way, a high percentage of overweight/obesity.

Crystal Structure of 4-Hydroxyphenylpyruvate Dioxygenase in Complex with Substrate Reveals a New Starting Point for Herbicide Discovery

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a promising target for drug and pesticide discovery. The unknown binding mode of substrate is still a big challenge for the understanding of enzymatic reaction mechanism and novel HPPD inhibitor design. Herein, we determined the first crystal structure of Arabidopsis thaliana HPPD (AtHPPD) in complex with its natural substrate (HPPA) at a resolution of 2.80 Å. Then, combination of hybrid quantum mechanics/molecular mechanics (QM/MM) calculations confirmed that HPPA takes keto rather than enol form inside the HPPD active pocket. Subsequent site-directed mutagenesis and kinetic analysis further showed that residues (Phe424, Asn423, Glu394, Gln307, Asn282, and Ser267) played important roles in substrate binding and catalytic cycle. Structural comparison between HPPA-AtHPPD and holo-AtHPPD revealed that Gln293 underwent a remarkable rotation upon the HPPA binding and formed H-bond network of Ser267-Asn282-Gln307-Gln293, resulting in the transformation of HPPD from an inactive state to active state. Finally, taking the conformation change of Gln293 as a target, we proposed a new strategy of blocking the transformation of HPPD from inactive state to active state to design a novel inhibitor with K_i value of 24.10 nM towards AtHPPD. The inhibitor has entered into industry development as the first selective herbicide used for the weed control in sorghum field. The crystal structure of AtHPPD in complex with the inhibitor (2.40 Å) confirmed the rationality of the design strategy. We believe that the present work provides a new starting point for the understanding of enzymatic reaction mechanism and the design of next generation HPPD inhibitors.

Unusual first presentation of a metabolic disorder

An 8-month-old boy presented to hospital with a fever, irritability and 'back arching'. On examination, he demonstrated profound opisthotonic posturing and had tonsillitis. He had a full septic screen and was treated with broad spectrum antibiotics. Blood tests showed a transaminitis, raised alpha fetoprotein and deranged clotting. The clotting abnormalities and raised alpha fetoprotein persisted post discharge and an abdominal ultrasound showed steatosis, splenomegaly and bilateral increased renal cortical reflectivity. A full metabolic screen revealed type 1 tyrosinaemia. The opisthotonic posturing, a major part of this child's presentation, has not been reported as a presenting feature of tyrosinaemia. It was part of a 'neurological crisis' caused by tyrosinaemia and exacerbated by the intercurrent infection. These are known to occur in tyrosinaemia but not commonly as the first presentation. This represents an unusual presentation of a metabolic condition which, without intervention, can lead to severe hepatic, renal and neurodevelopmental complications.

Autologous Gene and Cell Therapy Provides Safe and Long-Term Curative Therapy in A Large Pig Model of Hereditary Tyrosinemia Type 1

Orthotopic liver transplantation remains the only curative therapy for inborn errors of metabolism. Given the tremendous success for primary immunodeficiencies using ex-vivo gene therapy with lentiviral vectors, there is great interest in developing similar curative therapies for metabolic liver diseases. We have previously generated a pig model of hereditary tyrosinemia type 1 (HT1), an autosomal recessive disorder caused by deficiency of fumarylacetoacetate hydrolase (FAH). Using this model, we have demonstrated curative ex-vivo gene and cell therapy using a lentiviral vector to express FAH in autologous hepatocytes. To further evaluate the long-term clinical outcomes of this therapeutic approach, we continued to monitor one of these pigs over the course of three years. The animal continued to thrive off the protective drug NTBC, gaining weight appropriately, and maintaining sexual fecundity for the course of his life. The animal was euthanized 31 months after transplantation to perform a thorough biochemical and histological analysis. Biochemically, liver enzymes and alpha-fetoprotein levels remained normal and abhorrent metabolites specific to HT1 remained corrected. Liver histology showed no evidence of tumorigenicity and Masson's trichrome staining revealed minimal fibrosis and no evidence of cirrhosis. FAH-immunohistochemistry revealed complete repopulation of the liver by transplanted FAH-positive cells. A complete histopathological report on other organs, including kidney, revealed no abnormalities. This study is the first to demonstrate long-term safety and efficacy of hepatocyte-directed gene therapy in a large animal model. We conclude that hepatocyte-directed ex-vivo gene therapy is a rational choice for further exploration as an alternative therapeutic approach to whole organ transplantation for metabolic liver disease, including HT1.

Pediatric hepatocellular carcinoma

Pediatric hepatocellular carcinoma (HCC) is the second common malignant liver tumor in children after hepatoblastoma. It differs from the adult HCC in the etiological predisposition, biological behavior and lower frequency of cirrhosis. Perinatally acquired hepatitis-B virus, hepatorenal tyrosinemia, progressive familial intrahepatic cholestasis, glycogen storage disease, Alagille’s syndrome and congenital portosystemic shunts are important predisposing factors. Majority of children (87%) are older than 5 years of age. Following mass immunization against hepatitis-B, there has been a drastic fall in the incidence of new cases of pediatric HCC in the Asia-Pacific region. Management is targeted on complete surgical removal either by resection or liver transplantation. There is a trend towards improving survival of children transplanted for HCC beyond Milan criteria. Chemotherapeutic regimens do not offer good results but may be helpful for down-staging of advanced HCC. Surveillance of children with chronic liver diseases with ultrasound and alpha-fetoprotein may be helpful in timely detection, intervention and overall improvement in outcome of HCC.

The extent of liver injury determines hepatocyte fate toward senescence or cancer

It is well known that induction of hepatocyte senescence could inhibit the development of hepatocellular carcinoma (HCC). Until now, it is still unclear how the degree of liver injury dictates hepatocyte senescence and carcinogenesis. In this study, we investigated whether the severity of injury determines cell fate decisions between hepatocyte senescence and carcinogenesis. After testing of different degrees of liver injury, we found that hepatocyte senescence is strongly induced in the setting of severe acute liver injury. Longer-term, moderate liver injury, on the contrary did not result into hepatocyte senescence, but led to a significant incidence of HCC instead. In addition, carcinogenesis was significantly reduced by the induction of severe acute injury after chronic moderate liver injury. Meanwhile, immune surveillance, especially the activations of macrophages, was activated after re-induction of senescence by severe acute liver injury. We conclude that severe acute liver injury leads to hepatocyte senescence along with activating immune surveillance and a low incidence of HCC, whereas chronic moderate injury allows hepatocytes to proliferate rather than to enter into senescence, and correlates with a high incidence of HCC. This study improves our understanding in hepatocyte cell fate decisions and suggests a potential clinical strategy to induce senescence to treat HCC.

Daily variation of NTBC and its relation to succinylacetone in tyrosinemia type 1 patients comparing a single dose to two doses a day

INTRODUCTION

In hereditary tyrosinemia type 1 (HT1) patients, the dose of NTBC that leads to the absence of toxic metabolites such as succinylacetone (SA) is still unknown. Therefore, the aims of this study were to investigate the variation and concentrations of 2-(2-nitro-4-trifluormethyl-benzyl)-1,3-cyclohexanedione (NTBC) during the day in relation to the detection of SA, while comparing different dosing regimens.

METHODS

All patients were treated with NTBC (mean 1.08 ± 0.34 mg/kg/day) and a low phenylalanine-tyrosine diet. Thirteen patients received a single dose of NTBC and five patients twice daily. Home bloodspots were collected four times daily for three consecutive days measuring NTBC and SA concentrations. Statistical analyses were performed by using mixed model analyses and generalized linear mixed model analyses to study variation and differences in NTBC concentrations and the correlation with SA, respectively.

RESULTS

NTBC concentrations varied significantly during the day especially if NTBC was taken at breakfast only (p = 0.026), although no significant difference in NTBC concentrations between different dosing regimens could be found (p = 0.289). Momentary NTBC concentrations were negatively correlated with SA (p < 0.001). Quantitatively detectable SA was only found in subjects with once daily administration of NTBC and associated with momentary NTBC concentrations <44.3 μmol/l.

DISCUSSION

NTBC could be less stable than previously considered, thus dosing NTBC once daily and lower concentrations may be less adequate. Further research including more data is necessary to establish the optimal dosing of NTBC.

Current strategies for the treatment of inborn errors of metabolism

Inborn errors of metabolism (IEMs) are a large group of inherited disorders characterized by disruption of metabolic pathways due to deficient enzymes, cofactors, or transporters. The rapid advances in the understanding of the molecular pathophysiology of many IEMs, have led to significant progress in the development of many new treatments. The institution and continued expansion of newborn screening provide the opportunity for early treatment, leading to reduced morbidity and mortality. This review provides an overview of the diverse therapeutic approaches and recent advances in the treatment of IEMs that focus on the basic principles of reducing substrate accumulation, replacing or enhancing absent or reduced enzyme or cofactor, and supplementing product deficiency. In addition, the challenges and obstacles of current treatment modalities and future treatment perspectives are reviewed and discussed.

Mildly elevated succinylacetone and normal liver function in compound heterozygotes with pathogenic and pseudodeficient FAH alleles

Background

A high level of succinylacetone (SA) in blood is a sensitive, specific marker for the screening and diagnosis of hepatorenal tyrosinemia (HT1, MIM 276700). HT1 is caused by mutations in the FAH gene, resulting in deficiency of fumarylacetoacetate hydrolase. HT1 newborns are usually clinically asymptomatic, but have coagulation abnormalities revealing liver dysfunction. Treatment with nitisinone (NTBC) plus dietary restriction of tyrosine and phenylalanine prevents the complications of HT1

Observations

Two newborns screened positive for SA but had normal coagulation testing. Plasma and urine SA levels were 3–5 fold above the reference range but were markedly lower than in typical HT1. Neither individual received nitisinone or dietary therapy. They remain clinically normal, currently aged 9 and 15 years. Each was a compound heterozygote, having a splicing variant in trans with a prevalent “pseudodeficient” FAH allele, c.1021C > T (p.Arg341Trp), which confers partial FAH activity. All newborns identified with mild hypersuccinylacetonemia in Québec have had genetic deficiencies of tyrosine degradation: either deficiency of the enzyme preceding FAH, maleylacetoacetate isomerase, or partial deficiency of FAH itself.

Conclusion

Compound heterozygotes for c.1021C > T (p.Arg341Trp) and a severely deficient FAH allele have mild hypersuccinylacetonemia and to date they have remained asymptomatic without treatment. It is important to determine the long term outcome of such individuals.

A universal system to select gene-modified hepatocytes in vivo

Many genetic and acquired liver disorders are amenable to gene and/or cell therapy. However, the efficiencies of cell engraftment and stable genetic modification are low and often subtherapeutic. In particular, targeted gene modifications from homologous recombination are rare events. These obstacles could be overcome if hepatocytes that have undergone genetic modification were to be selectively amplified or expanded. We describe a universally applicable system for in vivo selection and expansion of gene-modified hepatocytes in any genetic background. In this system, the therapeutic transgene is coexpressed with a short hairpin RNA (shRNA) that confers modified hepatocytes with resistance to drug-induced toxicity. An shRNA against the tyrosine catabolic enzyme 4-OH-phenylpyruvate dioxygenase protected hepatocytes from 4-[(2-carboxyethyl)-hydroxyphosphinyl]-3-oxobutyrate, a small-molecule inhibitor of fumarylacetoacetate hydrolase. To select for specific gene targeting events, the protective shRNA was embedded in a microRNA and inserted into a recombinant adeno-associated viral vector designed to integrate site-specifically into the highly active albumin locus. After selection of the gene-targeted cells, transgene expression increased 10- to 1000-fold, reaching supraphysiological levels of human factor 9 protein (50,000 ng/ml) in mice. This drug resistance system can be used to achieve therapeutically relevant transgene levels in hepatocytes in any setting.

NTBC and Correction of Renal Dysfunction

Hereditary tyrosinemia type 1 (HT1) is characterized by severe progressive liver disease and renal tubular dysfunction. Kidney involvement is characterized by hypophosphatemic rickets and Fanconi syndrome. Different animal models were useful to investigate the pathophysiology of the disease and the effects of NTBC therapy on liver and kidney function. NTBC has revolutionized the prognosis of HT1 and its acute and chronic effects on renal tubular function have been proved, with normalization of tubular function within a few weeks, particularly hypophosphatemia and proteinuria. NTBC therapy is highly effective in improving renal function both at short and long-term. However, its efficacy critically depends on the age at start of treatment with normal outcome in patients diagnosed at birth by newborn screening.