Tyrosinemia type I and not treatment with NTBC causes slower learning and altered behavior in mice

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.

Impact of Nitisinone on the Cerebrospinal Fluid Metabolome of a Murine Model of Alkaptonuria

Background: Nitisinone-induced hypertyrosinaemia is well documented in Alkaptonuria (AKU), and there is uncertainty over whether it may contribute to a decline in cognitive function and/or mood by altering neurotransmitter metabolism. The aim of this work was to evaluate the impact of nitisinone on the cerebrospinal fluid (CSF) metabolome in a murine model of AKU, with a view to providing additional insight into metabolic changes that occur following treatment with nitisinone. Methods: 17 CSF samples were collected from BALB/c Hgd−/− mice (n = 8, treated with nitisinone—4 mg/L and n = 9, no treatment). Samples were diluted 1:1 with deionised water and analysed using a 1290 Infinity II liquid chromatography system coupled to a 6550 quadrupole time-of-flight mass spectrometry (Agilent, Cheadle, UK). Raw data were processed using a targeted feature extraction algorithm and an established in-house accurate mass retention time database. Matched entities (±10 ppm theoretical accurate mass and ±0.3 min retention time window) were filtered based on their frequency and variability. Experimental groups were compared using a moderated t-test with Benjamini−Hochberg false-discovery rate adjustment. Results: L-Tyrosine, N-acetyl-L-tyrosine, γ-glutamyl-L-tyrosine, p-hydroxyphenylacetic acid, and 3-(4-hydroxyphenyl)lactic acid were shown to increase in abundance (log2 fold change 2.6−6.9, 3/5 were significant p < 0.05) in the mice that received nitisinone. Several other metabolites of interest were matched, but no significant differences were observed, including the aromatic amino acids phenylalanine and tryptophan, and monoamine metabolites adrenaline, 3-methoxy-4-hydroxyphenylglycol, and octopamine. Conclusions: Evaluation of the CSF metabolome of a murine model of AKU revealed a significant increase in the abundance of a limited number of metabolites following treatment with nitisinone. Further work is required to understand the significance of these findings and the mechanisms by which the altered metabolite abundances occur.

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.

Network-Based Analysis of Cognitive Impairment and Memory Deficits from Transcriptome Data

Aging is an inevitable process that negatively affects all living organisms and their vital functions. The brain is one of the most important organs in living beings and is primarily impacted by aging. The molecular mechanisms of learning, memory and cognition are altered over time, and the impairment in these mechanisms can lead to neurodegenerative diseases. Transcriptomics can be used to study these impairments to acquire more detailed information on the affected molecular mechanisms. Here we analyzed learning- and memory-related transcriptome data by mapping it on the organism-specific protein-protein interactome network. Subnetwork discovery algorithms were applied to discover highly dysregulated subnetworks, which were complemented with co-expression-based interactions. The functional analysis shows that the identified subnetworks are enriched with genes having roles in synaptic plasticity, gliogenesis, neurogenesis and cognition, which are reported to be related to memory and learning. With a detailed analysis, we show that the results from different subnetwork discovery algorithms or from different transcriptomic datasets can be successfully reconciled, leading to a memory-learning network that sheds light on the molecular mechanisms behind aging and memory-related impairments.

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.

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.

Evaluation of the serum metabolome of patients with alkaptonuria before and after two years of treatment with nitisinone using LC-QTOF-MS

BACKGROUND

The homogentisic acid-lowering therapy nitisinone is being evaluated for the treatment of alkaptonuria (AKU) at the National Centre for AKU. Beyond hypertyrosinemia, the wider metabolic consequences of its use are largely unknown. The aim of this work was to evaluate the impact of nitisinone on the serum metabolome of patients with AKU after 12 and 24 months of treatment.

METHODS

Deproteinized serum from 25 patients with AKU (mean age[±SD] 51.1 ± 14.9 years, 12 male) was analyzed using the 1290 Infinity II liquid chromatography system coupled to a 6550 quadrupole time-of-flight mass spectrometry (Agilent, UK). Raw data were processed using a batch targeted feature extraction algorithm and an accurate mass retention time database containing 469 intermediary metabolites (MW 72-785). Matched entities (±10 ppm theoretical accurate mass and ±0.3 minutes retention time window) were filtered based on their frequency and variability (<25% CV) in group quality control samples, and repeated measures statistical significance analysis with Benjamini-Hochberg false discovery rate adjustment was used to assess changes in metabolite abundance.

RESULTS

Eight metabolites increased in abundance (log2 fold change [FC] 2.1-15.2, P < .05); 7 of 8 entities were related to tyrosine metabolism, and 13 decreased in abundance (log2 FC 1.5-15.5, P < .05); including entities related to tyrosine (n = 2), tryptophan (n = 3), xanthine (n = 2), and citric acid cycle metabolism (n = 2).

CONCLUSIONS

Evaluation of the serum metabolome of patients with AKU showed a significant difference in the abundance of several metabolites following treatment with nitisinone, including a number that have not been previously reported; several of these were not related to the tyrosine metabolic pathway.

SYNOPSIS

Nitisinone therapy has a significant impact on several metabolites beyond the tyrosine metabolic pathway, several of which appear to be related to the redox state of the cell.

Assessing the effect of nitisinone induced hypertyrosinaemia on monoamine neurotransmitters in brain tissue from a murine model of alkaptonuria using mass spectrometry imaging

OBJECTIVE

Nitisinone induced hypertyrosinaemia is a concern in patients with Alkaptonuria (AKU). It has been suggested that this may alter neurotransmitter metabolism, specifically dopamine and serotonin. Herein mass spectrometry imaging (MSI) is used for the direct measurement of 2,4-diphenyl-pyranylium tetrafluoroborate (DPP-TFB) derivatives of monoamine neurotransmitters in brain tissue from a murine model of AKU following treatment with nitisinone.

METHODS

Metabolite changes were assessed using MSI on DPP-TFB derivatised fresh frozen tissue sections directing analysis towards primary amine neurotransmitters. Matched tail bleed plasma samples were analysed using LC-MS/MS. Eighteen BALB/c mice were included in this study: HGD^-/- (n = 6, treated with nitisinone-4 mg/L, in drinking water); HGD^-/- (n = 6, no treatment) and HGD^+/- (n = 6, no treatment).

RESULTS

Ion intensity and distribution of DPP-TFB derivatives in brain tissue for dopamine, 3-methoxytyramine, noradrenaline, tryptophan, serotonin, and glutamate were not significantly different following treatment with nitisinone in HGD ^-/- mice, and no significant differences were observed between HGD^-/- and HGD^+/- mice that received no treatment. Tyrosine (10-fold in both comparisons, p = 0.003; [BALB/c HGD^-/- (n = 6) and BALB/c HGD^+/- (n = 6) (no treatment) vs. BALB/c HGD^-/- (n = 6, treated)] and tyramine (25-fold, p = 0.02; 32-fold, p = 0.02) increased significantly following treatment with nitisinone. Plasma tyrosine and homogentisic acid increased (ninefold, p = < 0.0001) and decreased (ninefold, p = 0.004), respectively in HGD^-/- mice treated with nitisinone.

CONCLUSIONS

Monoamine neurotransmitters in brain tissue from a murine model of AKU did not change following treatment with nitisinone. These findings have significant implications for patients with AKU as they suggest monoamine neurotransmitters are not altered following treatment with nitisinone.

Markers of cognitive function in individuals with metabolic disease: Morquio syndrome and tyrosinemia type III

We characterized cognitive function in two metabolic diseases. MPS-IVa (mucopolysaccharidosis IVa, Morquio) and tyrosinemia type III individuals were assessed using tasks of attention, language and oculomotor function. MPS-IVa individuals were slower in visual search, but the display size effects were normal, and slowing was not due to long reaction times (ruling out slow item processing or distraction). Maintaining gaze in an oculomotor task was difficult. Results implicated sustained attention and task initiation or response processing. Shifting attention, accumulating evidence and selecting targets were unaffected. Visual search was also slowed in tyrosinemia type III, and patterns in visual search and fixation tasks pointed to sustained attention impairments, although there were differences from MPS-IVa. Language was impaired in tyrosinemia type III but not MPS-IVa. Metabolic diseases produced selective cognitive effects. Our results, incorporating new methods for developmental data and model selection, illustrate how cognitive data can contribute to understanding function in biochemical brain systems.

Clinical and biochemical assessment of depressive symptoms in patients with Alkaptonuria before and after two years of treatment with nitisinone

OBJECTIVE

Concerns exist over hypertyrosinaemia that is observed following treatment with nitisinone. It has been suggested that tyrosine may compete with tryptophan for uptake into the central nervous system, and or inhibit tryptophan hydroxylase activity reducing serotonin production. At the National Alkaptonuria (AKU) Centre nitisinone is being used off-licence to treat AKU, and there is uncertainty over whether hypertyrosinaemia may alter mood. Herein results from clinical and biochemical assessments of depression in patients with AKU before and after treatment with nitisinone are presented.

PATIENTS AND METHODS

63 patients were included pre-nitisinone treatment, of these 39 and 32 patients were followed up 12 and 24 months after treatment. All patients had Becks Depression Inventory-II (BDI-II) assessments (scores can range from 0 to 63, the higher the score the more severe the category of depression), and where possible urinary monoamine neurotransmitter metabolites and serum aromatic amino acids were measured as biochemical markers of depression.

RESULTS

Mean (±standard deviation) BDI-II scores pre-nitisinone, and after 12 and 24 months were 10.1(9.6); 9.8(10.0) and 10.5(9.9) (p ≥ 0.05, all visits). Paired scores (n = 32), showed a significant increase at 24 months compared to baseline 10.5(9.9) vs. 8.6 (7.8) (p = 0.03). Serum tyrosine increased at least 6-fold following nitisinone (p ≤ 0.0001, all visits), and urinary 3-methoxytyramine (3-MT) increased at 12 and 24 months (p ≤ 0.0001), and 5-hydroxyindole acetic acid (5-HIAA) decreased at 12 months (p = 0.03).

CONCLUSIONS

BDI-II scores were significantly higher following 24 months of nitisinone therapy in patients that were followed up, however the majority of these patients remained in the minimal category of depression. Serum tyrosine and urinary 3-MT increased significantly following treatment with nitisinone. In contrast urinary 5-HIAA did not decrease consistently over the same period studied. Together these findings suggest nitisinone does not cause depression despite some observed effects on monoamine neurotransmitter metabolism.

Serum Amino Acid Profiling in Patients with Alkaptonuria Before and After Treatment with Nitisinone

BACKGROUND

Alkaptonuria (AKU) is a rare inherited disorder of the tyrosine metabolic pathway. Our group is evaluating the use of the homogentisic acid-lowering agent nitisinone in patients with AKU. A major biochemical consequence of this treatment is hypertyrosinaemia. Herein we report the concentration of 20 serum amino acids over a 36-month period pre- and post-treatment with nitisinone.

METHODS

Fasting serum samples were collected at baseline (pre-nitisinone), 3 (2 mg nitisinone every other day), 6, 12, 24 and 36 (2 mg nitisinone daily) months. Amino acids were measured using the Biochrom 30 high-performance liquid chromatography cation exchange system with ninhydrin detection.

RESULTS

Fifty patients [21 female, mean age (±standard deviation) 54.1 (15.6) years (range 25-75); 29 male, mean age 49.3 (11.6) years (range 22-70 years)] were included. Following treatment mean tyrosine concentrations increased seven- to eight-fold (baseline, 69.8 μmol/L; 3 months, 670.7 μmol/L; 6 months, 666.4 μmol/L; 12 months, 692.9 μmol/L; 24 months, 649.4 μmol/L; 36 months, 724.8 μmol/L, p = <0.001 for all visits compared to baseline).At baseline mean phenylalanine, aspartic acid and arginine were outside the normal reference range. Following treatment the ratios of phenylalanine/tyrosine, phenylalanine/large neutral amino acids, arginine/branched chain amino acids and branched chain/aromatic amino acids decreased (p = <0.05), and the tyrosine/large neutral amino acid ratio increased (p = <0.0001).

CONCLUSIONS

Marked hypertyrosinaemia was observed following treatment with nitisinone. Noteworthy changes were also observed in the ratio of several amino acids following treatment with nitisinone suggesting that the availability of amino acids for neurotransmitter biosynthesis and liver function may be altered following treatment with nitisinone.

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.

Assessment of the Effect of Once Daily Nitisinone Therapy on 24-h Urinary Metadrenalines and 5-Hydroxyindole Acetic Acid Excretion in Patients with Alkaptonuria After 4 Weeks of Treatment

BACKGROUND

One of the major metabolic consequences of using nitisinone to treat patients with alkaptonuria is that circulating tyrosine concentrations increase. As tyrosine is required for the biosynthesis of catecholamine neurotransmitters, it is possible that their metabolism is altered as a consequence. Herein we report the 24-h urinary excretion of normetadrenaline (NMA), metadrenaline (MA), 3-methoxytyramine (3-MT) (catecholamine metabolites) and 5-hydroxyindole acetic acid (5-HIAA, metabolite of serotonin) in a cohort of AKU patients before and after a 4-week treatment trial with nitisinone.

MATERIALS AND METHODS

24 h urinary excretions of NMA, MA, 3-MT and 5-HIAA were determined by liquid chromatography tandem mass spectrometry. Interassay coefficient of variation was <10% for all analytes measured, at all concentrations tested.

RESULTS

Urine samples were assayed at baseline (pre-nitisinone, n = 36) and 4 weeks later; 7 received no nitisinone (4 male, mean age (±SD) 46.3 (16.4) years), and 29 received a daily dose of nitisinone [1 mg (n = 7, 6 male, mean age 45.9 (10.9) years), 2 mg (n = 8, 5 male, mean age 43.9 (13.7) years), 4 mg (n = 8, 5 male, mean age 47.3 (10.7) years) and 8 mg (n = 6, 4 male, mean age 53.8 (8.3) years)]. 3-MT concentrations increase significantly (p < 0.01, at all doses) following nitisinone therapy but not in a dose-dependent manner. NMA concentrations decreased (p < 0.05, at all doses) following nitisinone therapy at all doses. 5-HIAA concentrations decreased following nitisinone therapy and were significantly lower at a daily dose of 8 mg only (p < 0.05).

CONCLUSIONS

This study shows that catecholamine and serotonin metabolism is altered by treatment with nitisinone.

Neurological and Neuropsychological Problems in Tyrosinemia Type I Patients

Clinically, Hereditary Tyrosinemia type I (HTI) is especially characterized by severe liver dysfunction in early life. However, recurrent neurological crises are another main finding in these patients when they are treated with a tyrosine and phenylalanine restricted diet only. This is caused by the accumulation of δ-aminolevulinic acid due to the inhibitory effect of succinylacetone on the enzyme that metabolizes δ-aminolevulinic acid. Due to the biochemical and clinical resemblance of these neurological crises and acute intermittent porphyria, this group of symptoms in HTI patients is mostly called porphyria-like-syndrome. The neurological crises in HTI patients disappeared after the introduction of treatment with 2-(2 nitro-4-3 trifluoro-methylbenzoyl)-1, 3-cyclohexanedione (NTBC). However, if NTBC treatment is stopped for a while, severe neurological dysfunction will reappear.If NTBC treatment is started early and given continuously, all clinical problems seem to be solved. However, recent research findings indicate that HTI patients have a non-optimal neurocognitive outcome, showing (among others) a lower IQ and impaired executive functioning and social cognition. Unfortunately the exact neuropsychological profile of these HTI patients is not known yet, neither are the exact pathophysiological mechanisms underlying these impairments. It may be hypothesized that the biochemical changes such as high blood tyrosine or low blood phenylalanine concentrations are important in this respect, but an direct toxic effect of NTBC or production of toxic metabolites (that previously characterized the disease before introduction of NTBC) cannot be excluded either. This chapter discusses the neurological and neuropsychological symptoms associated with HTI in detail. An extended section on possible underlying pathophysiological mechanisms of such symptoms is also included.