Long-term cognitive functioning in individuals with tyrosinemia type 1 treated with nitisinone and protein-restricted diet

Diagnosis, treatment, management and monitoring of patients with tyrosinaemia type 1: Consensus group recommendations from the German-speaking countries

Hepatorenal tyrosinaemia (HT1) is an autosomal recessive disorder of tyrosine degradation resulting in hepatic and renal dysfunction, neurological sequelae may occur in some patients. The use of nitisinone (NTBC) has revolutionised treatment and outcome of this disorder. NTBC has to be combined with a low protein diet. While NTBC modulates the disease course in HT1 patients, several issues are open. Optimal dosage, doses per day, therapeutic range of NTBC concentration, mode of protein restriction and biomarkers are not well defined. HCC and neurocognitive deficits are long-term sequelae. Early diagnosis and treatment are essential to minimise the risk for these complications. Clinical guidance for management of HT1-patients is required. Randomised clinical studies are difficult in the presence of therapeutic options. We discussed these issues in a consensus group of 10 paediatricians, 1 adult hepatologist, 1 geneticist, 2 dieticians, 2 newborn screening specialists with experience in HT1, 1 psychologist and 2 representatives of a patient group from the German-speaking countries (DACH). Recommendations were based on scientific literature and expert opinion, also taking into account recent experience with newborn screening. There was strong consensus that newborn screening using succinylacetone (SA) and early treatment are essential for a good outcome. The dose of NTBC should be as low as possible without losing metabolic control. This has to be accompanied by a low protein diet, in some patients a simplified diet without calculation of protein intake. Specific education and psychosocial support are recommended. Indications for liver transplantation were defined. Monitoring shall include clinical findings, levels of SA, tyrosine, phenylalanine and NTBC in (dried) blood.

Evaluation of a casein glycomacropeptide-based protein substitute, in the dietary management of NTBC-induced tyrosinaemia in patients with alkaptonuria: A prospective open-label study

BACKGROUND

2-(2-Nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) treatment of alkaptonuria (AKU) leads to increased blood tyrosine levels, causing skin issues and potentially sight-threatening corneal keratopathy. Adherence to dietary management of NTBC-induced tyrosinemia, a low-protein diet with or without protein substitutes, can be difficult for patients. This 28-day interventional study evaluated a low tyrosine casein glycomacropeptide (cGMP) protein substitute (TYR sphere)®, a 20 g protein equivalent, cGMP-based protein substitute, in terms of adherence, palatability, usability, comparison to amino acid (AA)-based protein substitutes, gastrointestinal tolerance and metabolic control in adults with NTBC-induced tyrosinaemia.

METHODS

Four adults (mean 61.1 years, range 53.3-69.3 years) with AKU and NTBC-induced tyrosinaemia were recruited from the United Kingdom National Alkaptonuria Centre (NAC). The cGMP protein substitute was prescribed based on individual nutritional requirements, replacing ≥1 AA-based protein substitute. Participants recorded product-related data in study diaries, using five-point Likert scales and daily and weekly logs. To determine metabolic control, prestudy blood tyrosine levels were compared to weekly blood spot tests during the study.

RESULTS

Median cGMP protein substitute adherence was 98%. Most participants rated palatability and usability positively, and preferred cGMP protein substitute to AA-based products. There were no notable gastrointestinal changes, and metabolic control was maintained.

CONCLUSIONS

cGMP protein substitute is a palatable and well-tolerated option in the dietary management of AKU patients with NTBC-induced tyrosinaemia.

A robust high-throughput screening system to assess bacterial tyrosine ammonia lyase activity in the context of tyrosine inherited metabolic disorders

Inborn errors of tyrosine metabolism result in patient's inability to degrade tyrosine. Current treatment consists of a phenylalanine and tyrosine restricted diet and nitisinone, causing a block in the tyrosine degradation pathway. However, tyrosine levels will increase, leading to acquired hypertyrosinemia, implying the need for an add-on treatment. Tyrosine ammonia lyases (TAL) can provide such an add-on treatment as they catalyze the deamination of tyrosine into p-coumaric acid and ammonia. In this study, we developed a robust high-throughput screening (HTS) assay to assess the capacity of bacterial TAL enzymes to decrease excessive tyrosine. The assay is based on the spectrophotometric quantification of p-coumaric acid after conversion of tyrosine by bacterial TAL. As a benchmark, TAL from Flavobacterium johnsoniae (FjTAL) was used to optimize the assay. Optimal growth conditions for high-level protein expression were determined by incubating transformed Escherichia coli BL21 (DE3) cells at different temperatures during various incubation times. Subsequently, assay temperature and pH were optimized followed by testing different ratios of tyrosine assay mixes to bacterial lysate. Finally, assay robustness and functionality were evaluated. Optimal FjTAL expression was obtained after incubation for 24 h at 22 °C. Ideal assay conditions consist of a 80/20 ratio of 1 mM tyrosine assay mix to FjTAL lysate performed at pH 9.2 and 37 °C. The robustness test showed Z' values > 0.4 and signal window values > 2 without edge or drift effects. As proof-of-principle, we successfully determined the catalytic activity of two other bacterial TAL enzymes RsTAL (5.718.10-3 ± 0.21.10-3) and SeSAM8 (4.658.10-3 ± 0.37.10-3). A robust, simple and reliable HTS assay was thus developed to evaluate the tyrosine degradation capacity of bacterial TAL enzymes.

UK guideline on the transition and management of childhood liver diseases in adulthood

INTRODUCTION

Improved outcomes of liver disease in childhood and young adulthood have resulted in an increasing number of young adults (YA) entering adult liver services. The adult hepatologist therefore requires a working knowledge in diseases that arise almost exclusively in children and their complications in adulthood.

AIMS

To provide adult hepatologists with succinct guidelines on aspects of transitional care in YA relevant to key disease aetiologies encountered in clinical practice.

METHODS

A systematic literature search was undertaken using the Pubmed, Medline, Web of Knowledge and Cochrane database from 1980 to 2023. MeSH search terms relating to liver diseases ('cholestatic liver diseases', 'biliary atresia', 'metabolic', 'paediatric liver diseases', 'autoimmune liver diseases'), transition to adult care ('transition services', 'young adult services') and adolescent care were used. The quality of evidence and the grading of recommendations were appraised using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system.

RESULTS

These guidelines deal with the transition of YA and address key aetiologies for the adult hepatologist under the following headings: (1) Models and provision of care; (2) screening and management of mental health disorders; (3) aetiologies; (4) timing and role of liver transplantation; and (5) sexual health and fertility.

CONCLUSIONS

These are the first nationally developed guidelines on the transition and management of childhood liver diseases in adulthood. They provide a framework upon which to base clinical care, which we envisage will lead to improved outcomes for YA with chronic liver disease.

Emotional and behavioural functioning in children with tyrosinaemia type 1

INTRODUCTION

Tyrosinaemia type I is a rare hereditary metabolic disease caused by deficiency of the enzyme involved in the breakdown of tyrosine. Since the use of nitisinone in addition to diet in 1992, survival rates have increased significantly, but more and more socio-emotional problems have become apparent. The aim of the study was the assessment the relationship between variations in serum tyrosine and phenylalanine levels and measurements of socio-emotional functioning and determination of patients' IQs.

THE AIM OF THE STUDY

was the assessment the relationship between variations in serum tyrosine and phenylalanine levels and measurements of socio-emotional functioning and determination of patients' IQs.

MATERIAL AND METHODS

Twelve children were studied, from a single centre, born between 1994 and 2012, treated with nitisinone and a low-phenylalanine and -tyrosine diet. The psychological evaluation was conducted using the parent form of the Child Behaviour Checklist (CBCL)/4-18. Additionally, the patients' IQs were measured using the Stanford-Binet 5 (SB5) Intelligence Scale. Statistical analyses were performed using PAWS software suite version 26. We found that phenylalanine variability over time correlated with measures of emotional and behavioural functioning. This relationship holds true for externalising behaviour, associated with the experience of maladjustment and aggression. Total score intellectual and cognitive function was within the norm for all patients.

CONCLUSIONS

To maintain better quality of life for patients and their families in terms of emotional and behavioural functioning, it may be important to avoid spikes (significant fluctuations) in phenylalanine levels. Regular, detailed psychological evaluations are recommended to detect potential problems and implement interventions aimed at achieving the best possible individual development and realise the intellectual and behavioural potential, thereby improving the patient's and her family's quality of life.

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.

mRNA-based therapy proves superior to the standard of care for treating hereditary tyrosinemia 1 in a mouse model

Hereditary tyrosinemia type 1 is an inborn error of amino acid metabolism characterized by deficiency of fumarylacetoacetate hydrolase (FAH). Only limited treatment options (e.g., oral nitisinone) are available. Patients must adhere to a strict diet and face a life-long risk of complications, including liver cancer and progressive neurocognitive decline. There is a tremendous need for innovative therapies that standardize metabolite levels and promise normal development. Here, we describe an mRNA-based therapeutic approach that rescues Fah-deficient mice, a well-established tyrosinemia model. Repeated intravenous or intramuscular administration of lipid nanoparticle-formulated human FAH mRNA resulted in FAH protein synthesis in deficient mouse livers, stabilized body weight, normalized pathologic increases in metabolites after nitisinone withdrawal, and prevented early death. Dose reduction and extended injection intervals proved therapeutically effective. These results provide proof of concept for an mRNA-based therapeutic approach to treating hereditary tyrosinemia type 1 that is superior to the standard of care.

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.

A case report of two siblings with hypertyrosinemia type 1 presenting with hepatic disease with different onset time and severity

Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive disorder caused by a defect in fumarylacetoacetate hydroxylase (FAH) encoded by the FAH gene. Patients with HT1 disorder present with increased blood tyrosine, succinyl acetoacetate, and succinyl acetone levels, and develop clinical manifestations including liver failure, kidney tubular dysfunction, growth failure, rickets, pseudo-porphyric crises, and hepatocellular carcinoma. We encountered two siblings with HT1. Among the siblings, the elder brother developed acute liver failure with coagulopathy at the age of 2 months and was rescued by liver transplantation (LT) following combination therapy with continuous hemodiafiltration and plasma exchange. The younger sister was followed up from the prenatal period for signs of HT1 due to prior history of the condition in her sibling. She was initially considered a carrier of HT1 owing to the lack of overt signs of the disease and negative urine screening for succinyl acetone (SA). She was eventually diagnosed with HT1 because of liver disorder at 9 months of age, associated with a positive urine SA result. Her disease state was controlled by treatment with nitisinone (NTBC). DNA analysis of both siblings identified heterozygous status for a previously reported FAH pathogenic allele (c.782C > T) and a novel likely pathogenic variant (c.688C.G). The siblings have stable lives with no developmental delay or impaired growth. NTBC treatment is effective in preventing the progression of liver and kidney diseases. However, even in cases treated without LT, clinicians should follow up the clinical outcomes over long term, as patients may require LT when developing complications, such as hepatocellular carcinoma.

In vivo lentiviral vector gene therapy to cure hereditary tyrosinemia type 1 and prevent development of precancerous and cancerous lesions

Conventional therapy for hereditary tyrosinemia type-1 (HT1) with 2-(2-nitro-4-trifluoromethylbenzoyl)−1,3-cyclohexanedione (NTBC) delays and in some cases fails to prevent disease progression to liver fibrosis, liver failure, and activation of tumorigenic pathways. Here we demonstrate cure of HT1 by direct, in vivo administration of a therapeutic lentiviral vector targeting the expression of a human fumarylacetoacetate hydrolase (FAH) transgene in the porcine model of HT1. This therapy is well tolerated and provides stable long-term expression of FAH in pigs with HT1. Genomic integration displays a benign profile, with subsequent fibrosis and tumorigenicity gene expression patterns similar to wild-type animals as compared to NTBC-treated or diseased untreated animals. Indeed, the phenotypic and genomic data following in vivo lentiviral vector administration demonstrate comparative superiority over other therapies including ex vivo cell therapy and therefore support clinical application of this approach.

Hereditary tyrosinemia type 1 (HT1) is an inborn error of metabolism caused by a deficiency in fumarylacetoacetate hydrolase (FAH). Here, the authors show in an animal model that HT1 can be treated via in vivo portal vein administration of a lentiviral vector carrying the human FAH transgene.

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.

Long-term low dose nitisinone therapy in adults with alkaptonuria shows no cognitive decline or increased severity of depression

Little is documented on whether nitisinone-induced hypertyrosinaemia alters cognitive functioning or leads to worsening depression in alkaptonuria (AKU). Wechsler Adult Intelligence Scale-IV (WAIS-IV) and Beck Depression Inventory-II (BDI-II) assessments were performed before and annually following treatment with nitisinone 2 mg daily to assess the impact on cognitive functioning and severity of depression. Serum tyrosine concentrations were also measured annually. WAIS-IV: 63 patients (27 females/36 males: mean age[years] [±standard deviation, range] 55.7[13.7, 26-79]; 60.3[9.6, 19-75]) were included at baseline for assessment of: verbal comprehension (VC), perceptual reasoning (PR), working memory (WM), and processing speed (PS) using separate indices. Over the 6-year period studied 43, 39, 36, 29, 26 and 15 patients had annual assessments. Using a longitudinal model (age and sex adjusted) no significant differences were observed in any of the indices over this period, apart from VC which showed a significant increase after adjustment for sex (p < 0.05). BDI-II: 74 patients (32 females/42 males: mean age[years] [±standard deviation, range] 56.1[13.2, 26-79]; 42 males, 51.5[16.3, 19-70]) were included at baseline. Over the 7-year period studied 48, 47, 38, 34, 32, 24 and 12 patients had annual assessments. No significant differences in BDI-II scores were observed when compared to baseline. Hypertyrosinaemia was observed in all patients following treatment with nitisinone (p < 0.001, at all annual visits). Serum tyrosine was not correlated with WAIS-IV sub-test indices or BDI-II scores pre- or post-nitisinone therapy. These findings suggest that treatment with nitisinone does not affect cognitive functioning and or lead to increased severity of depression.

Influence of nitisinone and its metabolites on l-tyrosine metabolism in a model system

Nitisinone (NTBC) is currently used for the treatment of tyrosinemia type 1, a rare disease. It also exhibits potential in the treatment of other orphan diseases as well as nervous system disorders - this is however limited by its side effects. In all living organisms, NTBC inhibits 4-hydroxyphenylpyruvate dioxygenase activity, thereby affecting l-tyrosine (L-TYR) catabolism, which results in the therapeutic effect. The NTBC metabolites formed in patient's body is one of the causes of its side effects. The influence of NTBC and its metabolites; 2-amino-4-(trifluoromethyl)benzoic acid, 2-nitro-4-(trifluoromethyl)benzoic acid, and cyclohexane-1,3-dione on L-TYR catabolism was investigated in Raphanus sativus var. longipinnatus. Based on targeted LC-MS/MS analysis the concentration of NTBC and its metabolites in exposed plant tissues was determined. Based on non-targeted LC-MS/MS analysis the concentrations of products of L-TYR catabolism: levodopa, epinephrine, norepinephrine, normetanephrine, dopamine, tyramine and vitamins C, B5 and B6, additionally leucine and valine were identified as influenced by the NTBC or its metabolites. NTBC and its metabolites influenced L-TYR catabolism differently. Particularly significant changes were found in the content of epinephrine and normetanephrine: in the plant tissues exposed to NTBC, an increase in the content of these neurotransmitters was found (+42%), whereas in the plant treated with 2-amino-4-(trifluoromethyl)benzoic acid or 2-nitro-4-(trifluoromethyl)benzoic acid a decrease in concentration (-39% and 55%, respectively) was observed. Cyclohexane-1,3-dione does not influence epinephrine and normetanephrine concentration. The conclusions of this study provide a platform for expanded research on the causes of side effects of NTBC treatment.

ADHD symptoms in neurometabolic diseases: Underlying mechanisms and clinical implications

Neurometabolic diseases (NMDs) are typically caused by genetic abnormalities affecting enzyme functions, which in turn interfere with normal development and activity of the nervous system. Although the individual disorders are rare, NMDs are collectively relatively common and often lead to lifelong difficulties and high societal costs. Neuropsychiatric manifestations, including ADHD symptoms, are prominent in many NMDs, also when the primary biochemical defect originates in cells and tissues outside the nervous system. ADHD symptoms have been described in phenylketonuria, tyrosinemias, alkaptonuria, succinic semialdehyde dehydrogenase deficiency, X-linked ichthyosis, maple syrup urine disease, and several mitochondrial disorders, but are probably present in many other NMDs and may pose diagnostic and therapeutic challenges. Here we review current literature linking NMDs with ADHD symptoms. We cite emerging evidence that many NMDs converge on common neurochemical mechanisms that interfere with monoamine neurotransmitter synthesis, transport, metabolism, or receptor functions, mechanisms that are also considered central in ADHD pathophysiology and treatment. Finally, we discuss the therapeutic implications of these findings and propose a path forward to increase our understanding of these relationships.

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).

Phenotype, genotype, and outcome of 25 Palestinian patients with hereditary tyrosinemia type 1

BACKGROUND

Tyrosinemia type 1 (hepatorenal tyrosinemia, HT1) is a rare autosomal recessive inborn error of tyrosine metabolism caused by deficiency of the last enzyme in the tyrosine catabolic pathway, fumarylacetoacetate hydrolase (FAH) leading to severe hepatic, renal and peripheral nerve damage if left untreated. Early treatment may prevent acute liver failure, renal dysfunction, liver cirrhosis, hepatocellular carcinoma (HCC) and improves survival.

MATERIAL AND METHODS

A retrospective single center study was carried out based on the clinical and biochemical presentation, therapy and outcome of 25 Palestinian patients with HT1 diagnosed during the last 25 years.

RESULTS

HT1 is not included in newborn screening program in Palestine. The mean age at diagnosis was 8 months and the main clinical manifestations were coagulopathy, hepatomegaly, splenomegaly and renal tubular dysfunction. The main biochemical abnormalities were elevated plasma tyrosine, serum transaminases and prothrombin time, and low serum phosphorous with elevated alkaline phosphatase compatible with hypophosphatemic rickets secondary to renal tubular dysfunction. All patients were treated with nitisinone. The mean duration of nitisinone treatment was 74 months and the mean dosage was 0.89 mg/kg/day. None developed HCC or neurological crisis.

CONCLUSIONS

Most patients present with liver failure and renal tubular dysfunction. Nitisinone treatment was effective therapy in all patients and improved both short- and long-term prognosis of HT1. Renal tubular dysfunction improved in all patients within the first week of starting nitisinone. Early diagnosis is necessary because delay in the treatment increases the risk of progressive liver failure HCC, progressive renal disease and neuropathy.

Hepatorenal Tyrosinaemia: Impact of a Simplified Diet on Metabolic Control and Clinical Outcome

Background: Tyrosinaemia type 1 is a rare inherited metabolic disease caused by an enzyme defect in the tyrosine degradation pathway. It is treated using nitisinone and a low-protein diet. In a workshop in 2013, a group of nutritional specialists from Germany, Switzerland and Austria agreed to advocate a simplified low-protein diet and to allow more natural protein intake in patients with tyrosinaemia type 1. This retrospective study evaluates the recommendations made at different treatment centers and their impact on clinical symptoms and metabolic control. Methods: For this multicenter study, questionnaires were sent to nine participating treatment centers to collect data on the general therapeutic approach and data of 47 individual patients treated by those centers. Results: Dietary simplification allocating food to 3 categories led to increased tyrosine and phenylalanine blood concentrations without weighing food. Phenylalanine levels were significantly higher in comparison to a strict dietary regimen whereas tyrosine levels in plasma did not change. Non-inferiority was shown for the simplification and liberalization of the diet. Compliance with dietary recommendations was higher using the simplified diet in comparison to the stricter approach. Age correlates negatively with compliance. Conclusions: Simplification of the diet with increased natural protein intake based on three categories of food may be implemented in the diet of patients with tyrosinaemia type 1 without significantly altering metabolic control. Patient compliance is strongly influencing tyrosine blood concentrations. A subsequent prospective study with a larger sample size is necessary to get a better insight into the effect of dietary recommendations on metabolic control.

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.

Nitisinone causes acquired tyrosinosis in alkaptonuria

For over two decades, nitisinone (NTBC) has been successfully used to manipulate the tyrosine degradation pathway and save the lives of many children with hereditary tyrosinaemia type 1. More recently, NTBC has been used to halt homogentisic acid accumulation in alkaptonuria (AKU) with evidence suggesting its efficacy as a disease modifying agent. NTBC-induced hypertyrosinaemia has been associated with cognitive impairment and potentially sight-threatening keratopathy. In the context of a non-lethal condition (ie, AKU), these serious risks call for an evaluation of the wider impact of NTBC on the tyrosine pathway. We hypothesised that NTBC increases the tyrosine pool size and concentrations in tissues. In AKU mice tyrosine concentrations of tissue homogenates were measured before and after treatment with NTBC. In humans, pulse injection with l-[¹³ C₉ ]tyrosine and l-[d₈ ]phenylalanine was used along with compartmental modelling to estimate the size of tyrosine pools before and after treatment with NTBC. We found that NTBC increased tyrosine concentrations in murine tissues by five to nine folds. It also significantly increased the tyrosine pool size in humans (P < .001), suggesting that NTBC increases tyrosine not just in serum but also in tissues (ie, acquired tyrosinosis). This study provides, for the first time, the experimental proof for the magnitude of NTBC-related acquired tyrosinosis which should be overcome to ensure the safe use of NTBC in AKU.

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.

Dried blood spot versus venous blood sampling for phenylalanine and tyrosine

BACKGROUND

This study investigated the agreement between various dried blood spot (DBS) and venous blood sample measurements of phenylalanine and tyrosine concentrations in Phenylketonuria (PKU) and Tyrosinemia type 1 (TT1) patients.

STUDY DESIGN

Phenylalanine and tyrosine concentrations were studied in 45 PKU/TT1 patients in plasma from venous blood in lithium heparin (LH) and EDTA tubes; venous blood from LH and EDTA tubes on a DBS card; venous blood directly on a DBS card; and capillary blood on a DBS card. Plasma was analyzed with an amino acid analyzer and DBS were analyzed with liquid chromatography-mass spectrometry. Agreement between different methods was assessed using Passing and Bablok fit and Bland Altman analyses.

RESULTS

In general, phenylalanine concentrations in LH plasma were comparable to capillary DBS, whereas tyrosine concentrations were slightly higher in LH plasma (constant bias of 6.4 μmol/L). However, in the low phenylalanine range, most samples had higher phenylalanine concentrations in DBS compared to LH plasma. Remarkably, phenylalanine and tyrosine in EDTA plasma were higher compared to all other samples (slopes ranging from 7 to 12%). No differences were observed when comparing capillary DBS to other DBS.

CONCLUSIONS

Overall agreement between plasma and DBS is good. However, bias is specimen- (LH vs EDTA), and possibly concentration- (low phenylalanine) dependent. Because of the overall good agreement, we recommend the use of a DBS-plasma correction factor for DBS measurement. Each laboratory should determine their own factor dependent on filter card type, extraction and calibration protocols taking the LH plasma values as gold standard.

Tyrosinemia Type 1 and symptoms of ADHD: Biochemical mechanisms and implications for treatment and prognosis

Hereditary tyrosinemia Type 1 (HT-1) is a rare metabolic disease where the enzyme catalyzing the final step of tyrosine breakdown is defect, leading to accumulation of toxic metabolites. Nitisinone inhibits the degradation of tyrosine and thereby the production of harmful metabolites, however, the concentration of tyrosine also increases. We investigated the relationship between plasma tyrosine concentrations and cognitive functions and how tyrosine levels affected enzyme activities of human tyrosine hydroxylase (TH) and tryptophan hydroxylase 2 (TPH2). Eight Norwegian children between 6 and 18 years with HT-1 were assessed using questionnaires measuring Attention Deficit Hyperactivity Disorder (ADHD)-symptoms and executive functioning. Recent and past levels of tyrosine were measured and the enzyme activities of TH and TPH2 were studied at conditions replicating normal and pathological tyrosine concentrations. We observed a significant positive correlation between mean tyrosine levels and inattention symptoms. While TH exhibited prominent substrate inhibition kinetics, TPH2 activity also decreased at elevated tyrosine levels. Inhibition of both enzymes may impair syntheses of dopamine, noradrenaline, and serotonin in brain tissue. Inattention in treated HT-1 patients may be related to decreased production of these monoamines. Our results support recommendations of strict guidelines on plasma tyrosine levels in HT-1. ADHD-related deficits, particularly inattention, should be monitored in HT-1 patients to determine whether intervention is necessary.

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.

Blood and Brain Biochemistry and Behaviour in NTBC and Dietary Treated Tyrosinemia Type 1 Mice

Tyrosinemia type 1 (TT1) is a rare metabolic disease caused by a defect in the tyrosine degradation pathway. Neurocognitive deficiencies have been described in TT1 patients, that have, among others, been related to changes in plasma large neutral amino acids (LNAA) that could result in changes in brain LNAA and neurotransmitter concentrations. Therefore, this project aimed to investigate plasma and brain LNAA, brain neurotransmitter concentrations and behavior in C57 Bl/6 fumarylacetoacetate hydrolase deficient (FAH−/−) mice treated with 2-(2-nitro-4-trifluoromethylbenoyl)-1,3-cyclohexanedione (NTBC) and/or diet and wild-type mice. Plasma and brain tyrosine concentrations were clearly increased in all NTBC treated animals, even with diet (p < 0.001). Plasma and brain phenylalanine concentrations tended to be lower in all FAH−/− mice. Other brain LNAA, were often slightly lower in NTBC treated FAH−/− mice. Brain neurotransmitter concentrations were usually within a normal range, although serotonin was negatively correlated with brain tyrosine concentrations (p < 0.001). No clear behavioral differences between the different groups of mice could be found. To conclude, this is the first study measuring plasma and brain biochemistry in FAH−/− mice. Clear changes in plasma and brain LNAA have been shown. Further research should be done to relate the biochemical changes to neurocognitive impairments in TT1 patients.

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.

Biomarkers of Micronutrients in Regular Follow-Up for Tyrosinemia Type 1 and Phenylketonuria Patients

Phenylketonuria (PKU) is treated with dietary restrictions and sometimes tetrahydrobiopterin (BH4). PKU patients are at risk for developing micronutrient deficiencies, such as vitamin B12 and folic acid, likely due to their diet. Tyrosinemia type 1 (TT1) is similar to PKU in both pathogenesis and treatment. TT1 patients follow a similar diet, but nutritional deficiencies have not been investigated yet. In this retrospective study, biomarkers of micronutrients in TT1 and PKU patients were investigated and outcomes were correlated to dietary intake and anthropometric measurements from regular follow-up measurements from patients attending the outpatient clinic. Data was analyzed using Kruskal-Wallis, Fisher's exact and Spearman correlation tests. Furthermore, descriptive data were used. Overall, similar results for TT1 and PKU patients (with and without BH4) were observed. In all groups high vitamin B12 concentrations were seen rather than B12 deficiencies. Furthermore, all groups showed biochemical evidence of vitamin D deficiency. This study shows that micronutrients in TT1 and PKU patients are similar and often within the normal ranges and that vitamin D concentrations could be optimized.

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.

Abnormal social behavior in mice with tyrosinemia type I is associated with an increase of myelin in the cerebral cortex

Hereditary tyrosinemia type I (HT1) is caused by mutations in the fumarylacetoacetate hydrolase (FAH) gene, the template for the final enzyme in the tyrosine catabolism pathway. If left untreated this deficiency of functional FAH leads to a buildup of toxic metabolites that can cause liver disease, kidney dysfunction and high mortality. The current treatment with the drug NTBC prevents the production of these metabolites and has consequently increased the survival rate in HT1 children. As a result of this increased survival, long term complications of HT1 are now being observed, including slower learning, impaired cognition and altered social behavior. We studied a mouse model of HT1 to gain insight into the effects of HT1 and treatment with NTBC on social behavior in mice. We showed that mice with HT1 display abnormal social behavior in that they spend more time in the absence of another mouse and do not discriminate between a novel mouse and an already familiar mouse. This altered behavior was due to HT1 and not treatment with NTBC. Quantification of cerebral cortex myelin in mice with HT1 showed a two to threefold increase in myelin expression. Our findings suggest that absence of FAH expression in the brain produces an altered brain biochemistry resulting in increased expression of myelin. This increase in myelination could lead to abnormal action potential velocity and altered neuronal connections that provide a mechanism for the altered learning, social behavior and cognitive issues recently seen in HT1.

Clinical utility of nitisinone for the treatment of hereditary tyrosinemia type-1 (HT-1)

Medical therapy for hereditary hepatorenal tyrosinemia (hereditary tyrosinemia type 1, HT-1) with nitisinone was discovered incidentally, and is a by-product of agrochemistry. It blocks the catabolic pathway of tyrosine, thereby leading to a reduction in the accumulation of toxic metabolites in HT-1. It has to be combined with a low-protein diet supplemented with amino acid mixtures devoid of tyrosine and phenylalanine. This treatment option has completely changed the clinical course of patients suffering from HT-1 who used to die in the first few months to years of life from liver failure, renal dysfunction, and/or hepatocellular carcinoma (HCC). It is essential to start nitisinone therapy early in life to avoid sequelae; beginning treatment in the newborn period is ideal. As initial clinical symptoms of HT-1 are often atypical and because there is a clinically latent phase during the first few months of life in many patients, newborn screening is required to secure early diagnosis. Succinylacetone in blood is a reliable screening parameter whereas tyrosine is neither specific nor sensitive. Especially HCC, but also liver and kidney dysfunction, rickets, and neurological crises can be prevented in most patients if nitisinone therapy is started in the newborn period. It is essential to adhere to a low-protein diet to avoid tyrosine toxicity. Reversible eye symptoms may occur as a side-effect of nitisinone, but other side effects are rare. Neurocognitive development is impaired in some patients, and the reason for this is unclear. Metabolic monitoring includes measurement of tyrosine, succinylacetone, and nitisinone concentrations in blood.