Joint replacement risk is markedly increased in alkaptonuria (AKU) in those with prior arthroplasty.

Background: Increased homogentisic acid (HGA) in alkaptonuria (AKU) causes severe arthritis. Nitisinone reduces the production of HGA, but whether it also decreases arthroplasty was examined in 237 AKU patients. Patients and methods: Patients attending the United Kingdom National Alkaptonuria Centre (NAC) and the Suitability of Nitisinone in Alkaptonuria 2 (SONIA 2) study were studied. Assessments included questionnaires eliciting details of arthroplasty. Nitisinone was administered from baseline, 2 mg in the NAC and 10 mg in SONIA 2. In SONIA 2, subgroups consisted of those with baseline arthroplasty on and not on nitisinone (BR + N+, BR + N-), as well as those without baseline arthroplasty on and not on nitisinone (BR-N+, BR-N-). Results: In the SONIA2 subgroups, new joint replacement (JR) probabilities after baseline were significantly different (BR + N+, BR + N-, BR-N+, BR-N-) (χ2 = 23.3, p < 0.001); mean (SD) was 3.8 (0.1) years in BR-N-, 3.7 (0.1) years in BR-N+, 3.4 (0.3) years in BR + N-, and 3.0 (0.3) years in BR + N+. Further, the BR + N- showed more JR than the BR-N- subgroup (p < 0.01), while BR + N+ similarly showed more JR than the BR-N+ subgroup (p < 0.001).In the NAC, the BR- group had a mean age of 51.6 (7.0) years at baseline but 57.7 (8.7) years at final follow up during nitisinone therapy and showed only 7 incident JR. The BR+ group had an age at baseline of 57.4 (8.5) years and had undergone 94 JRs at baseline. Conclusion: The incidence of arthroplasty was earlier and more frequent after the first JR and was not affected by nitisinone.

Nitisinone attenuates cartilage degeneration and subchondral osteoclastogenesis in osteoarthritis and concomitantly inhibits the cGAS/STING/NF-κB pathway.

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by cartilage degeneration and subchondral bone remodelling. Currently, conservative treatment strategies cannot effectively alleviate the progression of OA. In this study, we used computer network analysis to show that Nitisinone (NTBC) is closely related to extracellular matrix degradation in OA and mainly interferes with the TNF-α signaling pathway. NTBC is an orphan drug used to treat hereditary type I tyrosinemia by altering phenylalanine/tyrosine metabolic flow. In this study, we found that NTBC effectively reduced chondrocyte inflammation and extracellular matrix degradation induced by TNF-α. Mechanistically, NTBC inhibited the cGAS/STING signaling pathway and reduced activation of the STING-dependent NF-κB pathway to alleviate inflammation. In addition, NTBC inhibited osteoclastogenesis and delayed the occurrence of subchondral bone remodelling. In mice with ACLT-induced osteoarthritis, intra-articular injection of NTBC significantly reduced cartilage degradation and subchondral bone remodelling. NTBC showed impressive therapeutic efficacy as a potential pharmaceutical intervention for the treatment of OA.

A Lithuanian Case of Tyrosinemia Type 1 with a Literature Review: A Rare Cause of Acute Liver Failure in Childhood.

Hereditary type 1 tyrosinemia (HT1) is a rare inherited autosomal recessive disorder of tyrosine metabolism, characterized by progressive liver damage, dysfunction of kidney tubules, and neurological crises. In the course of this disease, due to the deficiency of the enzyme fumarylacetoacetate hydrolase (FAH), toxic intermediate metabolites of tyrosine breakdown, such as fumarylacetoacetate (FAA), succinylacetoacetate (SAA), and succinylacetone (SA), accumulate in liver and kidney cells, causing cellular damage. Because of this, an increased SA concentration in the blood or urine is pathognomonic of HT1. In the year 2000, HT1 was diagnosed in Lithuania for the first time, and this was the first time when a specific treatment for HT1 was administered in the country. Over two decades, four cases of this disease have been diagnosed in Lithuania. In the first of these patients, the disease was diagnosed in infancy, manifesting as liver damage with liver failure. Treatment with nitisinone was initiated, which continues to be administered, maintaining normal liver function. Liver transplantation was performed on two subsequent patients due to complications of HT1. It is crucial to diagnose HT1 as early as possible in order to reduce or completely eliminate complications related to the disease, including progressive liver failure and kidney dysfunction, among others. This can only be achieved by conducting a universal newborn screening for tyrosinemia and by starting treatment with nitisinone (NTBC) before the age of 1 month in all cases of HT1. However, in those countries where this screening is not being carried out, physicians must be aware of and consider this highly rare disorder. They should be vigilant, paying attention to even minimal changes in a few specific laboratory test results-such as unexplained anemia alongside neutropenia and thrombocytopenia-and should conduct more detailed examinations to determine the causes of these changes. In this article, we present the latest clinical case of HT1 in Lithuania, diagnosed at the Children's Diseases' Clinic of the Lithuanian University of Health Sciences (LUHS) Hospital Kaunas Clinics. The case manifested as life-threatening acute liver failure in early childhood. This article explores and discusses the peculiarities of diagnosing this condition in the absence of universal newborn screening for tyrosinemia in the country, as well as the course, treatment, and ongoing monitoring of patients with this disorder.

Electronic structure and molecular properties of nitisinone and mesotrione in water.

CONTEXT: Nitisinone is a medium-sized organic molecule that is used in treating hereditary tyrosinemia type 1 (HT-1). The structurally analogous mesotrione, however, is used as a pesticide/herbicide. What molecular properties are responsible for the similarity/dissimilarity of these molecules is investigated here. The solvent effect reduces the electron affinity to rather negative values and causes the negative electron affinity which manifests itself in a very high positive absolute reduction potential. METHODS: B3LYP method was utilized for a geometry optimization of nitisinone and mesotrione in their neural and ionized (L0, L+, L-) forms of 6 structures. The calculations were conducted in water as a solvent using conductor-like polarizable continuum model (CPCM), nitisinone also in vacuo. The complete vibrational analysis at the true energy minimum allows evaluating the thermodynamic functions with focus to the zero-point energy and overall entropic term. The change of the Gibbs energy on reductions and/or oxidation facilitates evaluating the absolute reduction and absolute oxidation potentials. Also, DLPNO-CCSD(T) method that involves the major part of the correlation energy has been applied to nitisinone and mesotrione and their molecular ions.

Increased prevalence of Parkinson's disease in alkaptonuria.

Amongst a cohort of 88 alkaptonuria (AKU) patients attending the United Kingdom National Alkaptonuria Centre (NAC), four unrelated patients had co-existing Parkinson's disease (PD). Two of the NAC patients developed PD before receiving nitisinone (NIT) while the other two developed overt PD during NIT therapy. NIT lowers redox-active homogentisic acid (HGA) and profoundly increases tyrosine (TYR). A further unpublished case of a Dutch patient with AKU and PD on deep brain stimulation is included in this report. A Pubmed search revealed a further five AKU patients with PD, all without NIT usage. The prevalence of PD in AKU in the NAC appears to be nearly 20-times higher than in the non-AKU population (p < 0.001) even when adjusted for age. We propose that life-long exposure to redox-active HGA may account for the higher prevalence of PD in AKU. Furthermore, the appearance of PD in AKU patients during NIT therapy may be due to unmasking dopamine deficiency in susceptible individuals, as a result of the tyrosinaemia during NIT therapy inhibiting the rate-limiting brain tyrosine hydroxylase.

Alkaptonuria - Past, present and future.

Alkaptonuria (AKU) is an ultra-rare inherited inborn error of metabolism that afflicts the tyrosine metabolic pathway, resulting in the accumulation of homogentisic acid (HGA) in the circulation, and significant excretion in urine. Clinical manifestations, typically observed from the third decade of life, are lifelong and significantly affect the quality of life. This review provides a comprehensive overview of the natural history of AKU, including clinical, biochemical and genetic perspectives. An update on the major advances on studies in murine models and human subjects, providing mechanistic insight into the molecular and biochemical processes that underlie pathophysiology and its response to treatment are presented. The impact of treatment with nitisinone is also presented with a specific emphasis on hypertyrosinemia, as uncertainty on this topic remains. Future perspectives are explored, such as novel approaches to treat hypertyrosinemia including the use of binding agents and amino acid transporter inhibitors, as well as advanced potentially curative gene and cell therapy initiatives.

A Previously Undiagnosed Case of Alkaptonuria in an 80-Year-Old Patient: A Case Report.

Alkaptonuria is a rare genetic metabolic disorder of autosomal recessive inheritance characterised by the accumulation of homogentisic acid in the body. It is diagnosed upon identification of characteristic symptoms, using various biochemical investigations, radiographic pictures, and a variety of specialised tests. Here we are discussing the case of an 80-year-old female patient with incidental findings of alkaptonuria. It is crucial to understand the fundamental diagnostic investigations that can be used in low-income nations or facilities where investigations like genetic testing, gas chromatography, and mass spectrometry are not readily available for the diagnosis of alkaptonuria.

Identification of Potential Inhibitors for the Treatment of Alkaptonuria Using an Integrated In Silico Computational Strategy.

Alkaptonuria (AKU) is a rare genetic autosomal recessive disorder characterized by elevated serum levels of homogentisic acid (HGA). In this disease, tyrosine metabolism is interrupted because of the alterations in homogentisate dioxygenase (HGD) gene. The patient suffers from ochronosis, fractures, and tendon ruptures. To date, no medicine has been approved for the treatment of AKU. However, physiotherapy and strong painkillers are administered to help mitigate the condition. Recently, nitisinone, an FDA-approved drug for type 1 tyrosinemia, has been given to AKU patients in some countries and has shown encouraging results in reducing the disease progression. However, this drug is not the targeted treatment for AKU, and causes keratopathy. Therefore, the foremost aim of this study is the identification of potent and druggable inhibitors of AKU with no or minimal side effects by targeting 4-hydroxyphenylpyruvate dioxygenase. To achieve our goal, we have performed computational modelling using BioSolveIT suit. The library of ligands for molecular docking was acquired by fragment replacement of reference molecules by ReCore. Subsequently, the hits were screened on the basis of estimated affinities, and their pharmacokinetic properties were evaluated using SwissADME. Afterward, the interactions between target and ligands were investigated using Discovery Studio. Ultimately, compounds c and f were identified as potent inhibitors of 4-hydroxyphenylpyruvate dioxygenase.

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.

Nutritional interventions for patients with alkaptonuria: A minireview.

Alkaptonuria (AKU, OMIM, No. 203500) is a rare, slow-progressing, irreversible, multisystemic disease resulting from a deficiency of the homogentisate 1,2-dioxygenase enzyme, which leads to the accumulation of homogentisic acid (HGA) and subsequent deposition as pigment in connective tissues called ochronosis. As a result, severe arthropathy of large joints and spondyloarthropathy with frequent fractures, ligament ruptures, and osteoporosis develops in AKU patients. Since 2020, the first-time treatment with nitisinone has become available in the European Union. Nitisinone significantly reduces HGA production and arrests ochronosis in AKU patients. However, blocking of the tyrosine metabolic pathway by the drug leads to tyrosine plasma and tissue concentrations increase. The nitisinone-induced hypertyrosinemia can lead to the development of corneal keratopathy, and once it develops, the treatment needs to be interrupted. A decrease in overall protein intake reduces the risk of the keratopathy during nitisinone-induced hypertyrosinemia in AKU patients. The low-protein diet is not only poorly tolerated by patients, but over longer periods, leads to a severe muscle loss and weight gain due to increased energy intake from carbohydrates and fats. Therefore, the development of novel nutritional approaches is required to prevent the adverse events due to nitisinone-induced hypertyrosinemia and the negative impact on skeletal muscle metabolism in AKU patients.

Clinical development innovation in rare diseases: overcoming barriers to successful delivery of a randomised clinical trial in alkaptonuria-a mini-review.

Alkaptonuria is a rare inherited disorder for which there was no disease-modifying treatment. In order to develop a successful approved therapy of AKU multiple barriers had to be overcome. These included activities before the conduct of the study including deciding on the drug therapy, the dose of the drug to be used, clarify the nature of the disease, develop outcome measures likely to yield a positive outcome, have a strategy to ensure appropriate patient participation through identification, build a consortium of investigators, obtain regulatory approval for proposed investigation plan and secure funding. Significant barriers were overcome during the conduct of the multicentre study to ensure harmonisation. Mechanisms were put in place to recruit and retain patients in the study. Barriers to patient access following completion of the study and regulatory approval were resolved.

Initial presentation, management and follow-up data of 33 treated patients with hereditary tyrosinemia type 1 in the absence of newborn screening.

Hereditary tyrosinemia type 1 (HT1) is a rare autosomal recessive disorder of phenylalanine and tyrosine catabolism due to a deficiency of fumarylacetoacetate hydrolase. HT1 has a large clinical spectrum with acute forms presenting before six months of age, subacute forms with initial symptoms occurring between age 6 and 12 months, and chronic forms after 12 months of age. Without treatment, HT1 results in the accumulation of toxic metabolites leading to liver disease, proximal tubular dysfunction, and porphyria-like neurological crises. Since the early nineties, the outcome of HT1 has dramatically changed due to its treatment with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC, nitisinone). In some countries, HT1 is included in the newborn screening program based on the analysis of succinylacetone concentration on dried blood spots. In the present study, we report clinical and laboratory parameters data on 33 HT1 patients focusing on clinical presentation and therapeutic management at the time of diagnosis. Eighteen patients were diagnosed with the acute form (median age at presentation 2.5 months), 6 with the subacute form (median age at presentation 10 months), and 5 with the chronic form of HT1 (median age at presentation 15 months). Four patients were diagnosed pre-symptomatically in the setting of a family history of HT1. Among the 29 symptomatic patients, hepatomegaly was found in 83% of patients and prolonged coagulation times due to hepatocellular insufficiency was observed in 93% of patients. HT1 diagnosis was confirmed by increased urine succinylacetone in all patients. All patients but 2 were treated with nitisinone immediately at diagnosis. During follow-up, 2 patients received liver transplant for high grade dysplasia or hepatocellular carcinoma, 10 patients exhibited some form of neurocognitive impairments. Our data confirm that HT1 is a severe treatable liver disease that should be detected at the earliest, ideally by newborn screening and appropriately treated.

The Discovery of the Mode of Action of Nitisinone.

This review briefly discusses the discovery of the mode of action of the triketone herbicide, 2-(2-nitro-4-trifluormethylbenzoyl)-1,3-cyclohexanedione and its use as a drug Nitisinone for the treatment of inborn errors of tyrosine metabolism. Nitisinone is a potent reversible tight-binding inhibitor of the enzyme 4-hydroxyphenylpyruvate dioxygenase, involved in the catabolism of the amino acid tyrosine. Nitisinone is used to treat the rare disease hereditary tyrosinaemia type 1 where the last enzyme in the breakdown of tyrosine, fumarylacetoacetase is deficient. Nitisinone is also used to treat patients with alkaptonuria where the enzyme homogentisic acid oxidase is deficient. Articles in this issue discuss metabolites of tyrosine catabolism in healthy patients and those with alkaptonuria.

Revisiting Quantification of Phenylalanine/Tyrosine Flux in the Ochronotic Pathway during Long-Term Nitisinone Treatment of Alkaptonuria.

Changes in the phenylalanine (PHE)/tyrosine (TYR) pathway metabolites before and during homogentisic acid (HGA)-lowering by nitisinone in the Suitability of Nitisinone in Alkaptonuria (AKU) 2 (SONIA 2) study enabled the magnitude of the flux in the pathway to be examined. SONIA 2 was a 48-month randomised, open-label, evaluator-blinded, parallel-group study performed in the UK, France and Slovakia recruiting patients with confirmed AKU to receive either 10 mg nitisinone or no treatment. Site visits were performed at 3 months and yearly thereafter. Results from history, photographs of eyes/ears, whole body scintigraphy, echocardiography and abdomen/pelvis ultrasonography were combined to produce the Alkaptonuria Severity Score Index (cAKUSSI). PHE, TYR, hydroxyphenylpyruvate (HPPA), hydroxyphenyllactate (HPLA) and HGA metabolites were analysed by liquid chromatography/tandem mass spectrometry in 24 h urine and serum samples collected before and during nitisinone. Serum metabolites were corrected for total body water (TBW), and the sum of 24 h urine plus total body water metabolites of PHE, TYR, HPPA, HPLA and HGA were determined. The sum of urine metabolites (PHE, TYR, HPPA, HPLA and HGA) were similar pre- and peri-nitisinone. The sum of TBW metabolites and sum TBW + URINE metabolites were significantly higher peri-nitisinone (p < 0.001 for both) compared with pre-nitisinone baseline. Significantly higher concentrations of metabolites from the tyrosine metabolic pathway were observed during treatment with nitisinone. Arguments for unmasking of the ochronotic pathway and biliary elimination of HGA are put forward.

Adequacy of nitisinone for the management of alkaptonuria.

Alkaptonuria is a rare hereditary disease with a defective enzyme that results in increased homogentisic acid levels in the body. Homogentisic acid accumulates in multiple body parts and initializes tissue damage. Clinical manifestations such as pigmentation of the skin areas and joint destruction result in ochronosis. Nitisinone decreases serum and urinary homogentisic acid levels, improving morbidity by preventing and slowing the progression of alkaptonuria. Nitisinone-induced hypertyrosinemia causes keratopathy and mental ill effects, which can be managed by diet restriction and regular check-ups. A personalized approach is required for treatment by nitisinone. Low-dose oral nitisinone is associated with overall good results and a better safety profile.

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.

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.

Improving the clinical accuracy and flexibility of the Alkaptonuria severity score index.

Alkaptonuria (AKU) is a rare genetic disorder where oxidised homogentisic acid accumulates in connective tissues, leading to multisystem disease. The clinical evaluation Alkaptonuria Severity Score Index (cAKUSSI) is a composite score that assesses the extent of AKU disease. However, some components assess similar disease features, are difficult to measure reliably or cannot be measured in resource-limited environments. cAKUSSI data from the 4-year SONIA 2 randomised controlled trial, which investigated nitisinone treatment in adults with AKU, were analysed (N = 125). Potentially biased or low-information cAKUSSI measurements were identified using clinical and statistical input to create a revised AKUSSI for use in AKU research (cAKUSSI 2.0). Additionally, resource-intensive measurements were removed to explore a flexible AKUSSI (flex-AKUSSI) for use in low-resource environments. Revised scores were compared to cAKUSSI in terms of correlation and how they capture disease progression and treatment response. Eight measurements were removed from the cAKUSSI to create the cAKUSSI 2.0, which performed comparably to the cAKUSSI in measuring disease extent, progression and treatment response. When removing resource-intensive measurements except for osteoarticular disease, the flex-AKUSSI was highly correlated with the cAKUSSI, indicating that they quantified disease extent similarly. However, when osteoarticular disease (measured using scans) was removed, the corresponding flex-AKUSSI underestimated disease progression and overestimated treatment response compared to the cAKUSSI. Clinicians may use the cAKUSSI 2.0 to reduce time, effort and patient burden. Clinicians in resource-limited environments may find value in computing a flex-AKUSSI score, offering potential for future global registries to expand knowledge about AKU.

Association of alkaptonuria and low dose nitisinone therapy with cataract formation in a large cohort of patients.

Homogentisic acid (HGA) lowering, disease modifying off-label nitisinone therapy has been used in the United Kingdom National Alkaptonuria Centre (NAC) since 2012. This study evaluated the serendipitous observation of cataract in a large cohort of patients with the very rare disease alkaptonuria (AKU), over a 5-year period. Patients with AKU who attended the NAC since 2012. Standard physical examination and ocular assessment, including photographs of the crystalline lens were taken before commencement of nitisinone 2 mg daily and annually over 5 years. Photographs were randomised and graded by two independent observers using the WHO cataract classification. AKU patients who did not receive nitisinone were included as a control group. HGA was measured on acidified 24 h urine (u-HGA24) and HGA and tyrosine in fasting acidified serum samples (sHGA, sTYR) at each visit. Patients without suitable lens images were excluded. Cataract (mean grade 1) was noted at baseline in 47 out of 62 (76%) with a mean (SD) age of 44 (14) years. In nitisinone-treated patients, there were significant increases in the mean grade of nuclear (0.18, p < 0.01) and cortical (0.38, p < 0.01) lens opacities over the mean duration of 4.93 years of the study. Worsening of the nuclear cataract and cortical lens opacities by at least 1 grade was noted in 14 out of 46 (30%) and 11 out of 46 (24%) patients, respectively. There is an increased prevalence and progression of cataract in AKU and a possible association of nitisinone with cataract progression.

Method development and validation for analysis of phenylalanine, 4-hydroxyphenyllactic acid and 4-hydroxyphenylpyruvic acid in serum and urine.

Alkaptonuria (AKU) is a rare debilitating autosomal recessive disorder of tyrosine (TYR) metabolism which results in a deficiency of the enzyme homogentisate 1,2-dioxygenase activity. Several studies have reported the metabolic changes in homogentisic acid (HGA) concentrations and subsequent deposition of an ochronotic pigment in connective tissues, especially cartilage. Treatment with nitisinone (NTBC) reduces urinary and circulating HGA, but its mode of action results in hypertyrosinaemia. The effect of NTBC on other metabolites in the TYR pathway has not been reported. Modification of the current reverse phase liquid chromatography tandem mass spectrometry methods for serum and urine to include phenylalanine (PHE), hydroxyphenyllactate (HPLA) and hydroxyphenylpyruvate (HPPA) has been validated. HPPA and HPLA (negative ionisation) eluted at 2.8 and 2.9 min respectively on an Atlantis C18 column with PHE (positive ionisation) eluting earlier at 2.4 min. Intra- and inter-assay accuracy was between 96.3% and 100.3% for PHE; 96.6% and 110.5% for HPLA and 95.0% and 107.8% for HPPA in both urine and serum. Precision, both inter- and intra-assay, was <10% for all analytes in both serum and urine. No significant issues with carry-over, stability or matrix interferences were seen in either the urine or serum assays. Measurement of serum and urine from AKU patients has demonstrated a robust, fully validated assay, appropriate for monitoring of patients with AKU and for demonstrating metabolite changes, following NTBC therapy.