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.

Perioperative anaesthetic management of an elderly high-risk male with cardiac ochronosis undergoing aortic valve replacement with coronary artery bypass graft: A case report

Alkaptonuria is a rare autosomal recessive congenital disorder of metabolism that affects 1 in 250,000 live births. It manifests as ochronosis and degenerative arthritis due to the accumulation of homogentistic acid in cartilage and heart valves along with precipitation of renal, salivary, pancreatic and gall bladder calculi. It is noted to cause cardiac valve stenosis and regurgitation secondary to calcification leading to cardiac failure in 10% of patients. Through this report, we present a successful perioperative anaesthetic management of a 74-year-old man with cardiac ochronosis, who underwent an aortic valve replacement with coronary artery bypass graft surgery at our centre.

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.

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.

Ochronotic arthropathy of bilateral hip joints: A case report

BACKGROUND

Ochronosis, also known as alkaptonuria, is a rare autosomal recessive self-metabolic disease arising from deficiency of homogentisate 1,2 dioxygenase enzyme. It affects several organs and muscoskeletal structures. We herein report a case of a patient who presented with severe hip arthropathy complicated with late stage ochronosis.

CASE SUMMARY

A 56-year-old male patient was admitted in our department in 2019 with complaints of chronic low backache and left hip pain. After the required investigations were done, lumbar disc herniation and severe hip arthritis were the initial diagnosis. A total left hip arthroplasty was performed. Ochronotic osteoarthritis was only obtained post-surgery as confirmatory diagnosis. He was again admitted mid 2022 with the same complaints on the right hip. Subsequently, he underwent a total right hip arthroplasty. Post-operative recovery and follow-ups were deemed very satisfactory.

CONCLUSION

Ochronosis is an unusual diagnosis for a patient who presents with typical hip arthritis. Thus, unless meticulous history taking and advanced laboratory tests, the diagnosis can easily be missed by surgeons.

Determinants of tyrosinaemia during nitisinone therapy in alkaptonuria

Nitisinone (NIT) produces inevitable but varying degree of tyrosinaemia. However, the understanding of the dynamic adaptive relationships within the tyrosine catabolic pathway has not been investigated fully. The objective of the study was to assess the contribution of protein intake, serum NIT (sNIT) and tyrosine pathway metabolites to nitisinone-induced tyrosinaemia in alkaptonuria (AKU). Samples of serum and 24-h urine collected during SONIA 2 (Suitability Of Nitisinone In Alkaptonuria 2) at months 3 (V2), 12 (V3), 24 (V4), 36 (V5) and 48 (V6) were included in these analyses. Homogentisic acid (HGA), tyrosine (TYR), phenylalanine (PHE), hydroxyphenylpyruvate (HPPA), hydroxyphenyllactate (HPLA) and sNIT were analysed at all time-points in serum and urine. Total body water (TBW) metabolites were derived using 60% body weight. 24-h urine and TBW metabolites were summed to obtain combined values. All statistical analyses were post-hoc. 307 serum and 24-h urine sampling points were analysed. Serum TYR from V2 to V6, ranging from 478 to 1983 µmol/L were stratified (number of sampling points in brackets) into groups < 701 (47), 701–900 (105), 901–1100 (96) and > 1100 (59) µmol/L. The majority of sampling points had values greater than 900 µmol/L. sPHE increased with increasing sTYR (p < 0.001). Tyrosine, HPPA and HPLA in serum and TBW all increased with rising sTYR (p < 0.001), while HPLA/TYR ratio decreased (p < 0.0001). During NIT therapy, adaptive response to minimise TYR formation was demonstrated. Decreased conversion of HPPA to HPLA, relative to TYR, seems to be most influential in determining the degree of tyrosinaemia.

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.

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.

Efficacy of Phenylalanine- and Tyrosine-Restricted Diet in Alkaptonuria Patients on Nitisinone Treatment: Case Series and Review of Literature

INTRODUCTION

Nitisinone used in alkaptonuria (AKU) can result in keratopathy due to strongly increased tyrosine levels.

METHODS

This study aimed to investigate nutritional status and changes in plasma tyrosine and phenylalanine and urinary homogentisic acid (u-HGA) levels in 8 adult AKU patients (mean age, 56.3 ± 4.7 years) who were on tyrosine/phenylalanine-restricted diet together with 2 mg/day nitisinone.

RESULTS

The treatment period was 23.4 ± 6.9 months. Daily dietary protein intake was restricted to 0.8-1.0 g/kg/day. Daily tyrosine intake was restricted to 260-450 mg/day for females and 330-550 mg/day for males. Tyrosine/phenylalanine-free amino acid supplements accounted for an average of 56.1% of daily protein intake. The following assessments were performed: anthropometric and plasma tyrosine level measurements every 2 months; ophthalmological examination every 6 months, and nutritional laboratory analyses and measurements of plasma amino acids and u-HGA once in a year. It was targeted to keep the plasma tyrosine level <500 μmol/L. The plasma tyrosine level was <100 μmol/L before the treatment in all patients and around a mean of 582.5 ± 194.8 μmol/L during the treatment. The diet was rearranged if a plasma tyrosine level of >700 μmol/L was detected. The u-HGA level before and after the 1st year of treatment was 1,429.3 ± 1,073.4 mmol/mol creatinine and 33.6 ± 9.5 mmol/mol creatinine, respectively. None of the patients developed keratopathy or experienced weight loss and protein or micronutrient deficiency.

CONCLUSION

AKU patients should receive tyrosine/phenylalanine-restricted diet for reducing plasma tyrosine level to the safe range. Tyrosine/phenylalanine-free amino acid supplements can be safely used to enhance dietary compliance. Keratopathy and nutrient deficiency should be frequently monitored.

Preventive use of nitisinone in alkaptonuria

Alkaptonuria (AKU, OMIM 203500) is a rare congenital disorder caused by a deficiency of the enzyme homogentisate-1,2,-dioxygenase. The long-term consequences of AKU are joint problems, cardiac valve abnormalities and renal problems. Landmark intervention studies with nitisinone 10 mg daily, suppressing an upstream enzyme activity, demonstrated its beneficial effects in AKU patients with established complications, which usually start to develop in the fourth decade. Lower dose of nitisinone in the range of 0.2–2 mg daily will already reduce urinary homogentisic acid (uHGA) excretion by > 90%, which may prevent AKU-related complications earlier in the course of the disease while limiting the possibility of side-effects related to the increase of plasma tyrosine levels caused by nitisinone. Future preventive studies should establish the lowest possible dose for an individual patient, the best age to start treatment and also collect evidence to which level uHGA excretion should be reduced to prevent complications.

Evaluating the aortic stenosis phenotype before and after the effect of homogentisic acid lowering therapy: Analysis of a large cohort of eighty-one alkaptonuria patients

AIMS

A large alkaptonuria (AKU) cohort was studied to better characterise the poorly understood phenotype of aortic stenosis of rare disease AKU.

METHODS AND RESULTS

Eighty-one patients attended the National Alkaptonuria Centre (NAC) between 2007 and 2020. Nine only attended once. Fifty-one attended more than once and received nitisinone 2 mg daily. Twenty-one attended at least twice without receiving nitisinone. Assessments included questionnaire analysis, standard transthoracic echocardiography, as well as photographs of ochronotic pigment in eyes and ears at baseline when 2 mg nitisinone was commenced, and yearly thereafter. Blood and urine samples were collected for chemical measurement. The prevalence of aortic stenosis and aortic valve replacement were 22.2 and 6.2% in the current group. Aortic maximum velocity (Vmax) was directly related to varying degrees to age (R = 0.58, p < 0.001), systolic blood pressure (R = 0.32, p < 0.05), serum homogentisic acid (sHGA) (R = 0.28, p < 0.05), ochronosis scores (R = 0.72, p < 0.001), and alkaptonuria severity score index (AKUSSI) (R = 0.58, p < 0.001) on linear regression analysis. Age and ochronosis scores were significantly related to Vmax on multiple regression analysis (p < 0.005). Nitisinone decreased sHGA, 24-h urine HGA (uHGA₂₄₎, ochronosis scores and AKUSSI significantly at all visits post-nitisinone. Nitisinone decreased Vmax change scores at final visit comparison, with a similar pattern at earlier visits.

CONCLUSION

Aortic valve disease is highly prevalent in this NAC cohort, and strongly associated with ochronosis and disease severity. Nitisinone decreases ochronosis and had a similar significant effect on Vmax.

Development of an Effective Therapy for Alkaptonuria - Lessons for Osteoarthritis

Osteoarthritis (OA) is one of the major causes of disability and pain worldwide, yet despite a massive international research effort, no effective disease-modifying drugs have been identified to date. In this review, we put forward the proposition that greater focus on rarer forms of OA could lead to a better understanding of the pathogenesis of more common OA. We have investigated the severe osteoarthropathy of the ultra-rare disease alkaptonuria (AKU). In addition to the progress made in finding a treatment for AKU, our research has revealed important lessons for more common OA, including the identification of high-density mineralized protrusions (HDMPs), new pathoanatomical structures which may play an important role in joint destruction and pain in AKU and in OA. AKU is an inherited disorder of tyrosine metabolism, caused by genetic lack of the enzyme homogentisate 1,2 dioxygenase (HGD), which leads to failure to breakdown homogentisic acid (HGA). While most HGA is excreted over time, some of it is deposited as a pigment in connective tissues, a process described as ochronosis. Ochronotic pigment alters the mechanical properties of tissues, leading to inevitable joint destruction and frequently to cardiac valve disease. Until recently, there was no effective therapy for AKU, but preclinical studies demonstrated that upstream inhibition of tyrosine metabolism by nitisinone, a drug previously used in hereditary tyrosinaemia 1 (HT1), completely prevented ochronosis in AKU mice. This was followed by successful clinical trials which have resulted in nitisinone being approved for therapy of AKU by the European Medicines Agency, making AKU the only cause of OA for which there is an effective therapy to date. Study of other rare causes of OA should be a higher priority for researchers and funders to ensure further advances in understanding and eventual therapy of OA.

Characterizing the alkaptonuria joint and spine phenotype and assessing the effect of homogentisic acid lowering therapy in a large cohort of 87 patients

A large alkaptonuria (AKU) cohort was studied to better characterize the poorly understood spondyloarthropathy of rare disease AKU. Eighty-seven patients attended the National Alkaptonuria Centre (NAC) between 2007 and 2020. Seven only attended once. Fifty-seven attended more than once and received nitisinone 2 mg daily. Twenty-three attended at least twice without receiving nitisinone. Assessments included questionnaire analysis, ^18F Positron emission tomography computerised tomography (PETCT), as well as photographs of ochronotic pigment in eyes and ears at baseline when 2 mg nitisinone was commenced and yearly thereafter. Blood and urine samples were collected for chemical measurement. The prevalence of ochronosis, as well as pain, PETCT and combined pain and PETCT scores, was greatly increased at 90.5%, 85.7%, 100%, and 100%, respectively. Joint pain scores were greatest in proximal joints in upper and lower limbs. PETCT joint scores were higher in proximal joints in upper limb but higher in distal joints in the lower limb. Spine pain scores were highest in lumbar, followed by cervical, thoracic, and cervical regions at 77.4%, 59.5%, 46.4%, and 25%, respectively. PETCT spine scores were highest in thoracic followed by lumbar, cervical, and sacroiliac regions at 74.4%, 70.7%, 64.6%, and 47.8% respectively; ochronosis associated closely with spondyloarthropathy scores (R = .65; P < .0001). Nitisinone reversed ochronosis significantly, with a similar pattern of decreased joint and spine disease. Spondyloarthropathy is a highly prevalent feature in this NAC cohort. Ochronosis appears to be associated with spondyloarthropathy. Nitisinone decreases ochronosis and had a similar nonsignificant effect pattern on spondyloarthropathy.

Characterising the arthroplasty in spondyloarthropathy in a large cohort of eighty-seven patients with alkaptonuria

Arthroplasty in the spondyloarthropathy (SPOND) of alkaptonuria (AKU) in incompletely characterised. The aim was to improve the understanding of arthroplasty in AKU through a study of patients attending the National Alkaptonuria Centre (NAC). Eighty-seven patients attended the NAC between 2007 and 2020. Seven only attended once. Fifty-seven attended more than once and received nitisinone 2 mg daily. Twenty-three attended at least twice without receiving nitisinone. Assessments including questionnaire analysis eliciting details of arthroplasty and other surgical treatments for SPOND, ¹⁸ FPETCT and CT densitometry at the neck of hip and lumbar spine, as well as photographs of the eyes and ears were acquired from patients attending the National Alkaptonuria Centre (NAC) at baseline when 2 mg nitisinone was commenced, and yearly thereafter. Photographs were scored to derive ochronosis scores. Blood and urine samples were collected for chemical analyses. The prevalence of arthroplasty was 36.8%, similar in males and females, occurring especially in the knees, hips and shoulders. Multiple arthroplasties were found in 29 patients (33.3%) in this cohort. Incident arthroplasty was 6.5% in the nitisinone group and 7.1% in the no-nitisinone group. Incident arthroplasty was 11.3% in the group with baseline arthroplasty and 3.51% in the group without. A strong association of arthroplasty with SPOND (R = 0.5; P << .0001) and ochronosis (R = 0.54; P < .0001) was seen. Nitisinone had no significant effect on incident arthroplasty. Arthroplasty due to ochronosis and SPOND is common in AKU. Nitisinone decreased ochronosis but had no effect on arthroplasty in this cohort.

A case report of pregnancy in untreated alkaptonuria - Focus on urinary tissue remodelling markers

A 34-year old woman with alkaptonuria had an elective pregnancy, during which she collected urine samples over the duration of her pregnancy until parturition. She had been attending the National Alkaptonuria Centre from the age of 31 years and continued to attend after delivery for a further three annual visits. Data from her NAC visits as well as urine samples collected during pregnancy were analysed. Urine CTX-1/urine creatinine, urine αCTX-I/ urine creatinine, urine CTX-II/ urine creatinine, and urine C3M/urine creatinine all showed a rapid increase early in pregnancy, returning to baseline before increasing in late pregnancy, indicating significant remodelling of bone, subchondral bone, cartilage and other organs and connective tissue rich in collagens I, II and III. The pattern of tissue remodelling in AKU pregnancy has been described for the very first time. Further research is needed to understand pregnancy in AKU.

Alkaptonuria in Turkey: Clinical and molecular characteristics of 66 patients

Alkaptonuria (AKU) is an inborn error of metabolism caused by the deficiency of homogentisate 1,2-dioxygenase (HGD) as a result of a defect in the HGD gene. HGD enzyme deficiency results in accumulation of homogentisic acid (HGA) in the body, which in turn leads to multisystemic clinical symptoms. The present study aimed to investigate the presenting symptoms, age at diagnosis, and clinical and genetic characteristics of AKU patients followed-up in different centers in Turkey. In this cross-sectional, multicenter, descriptive study, medical records of 66 AKU patients were retrospectively evaluated. Patients' data regarding demographic, clinical and genetic characteristics were recorded. HGD database (http://hgddatabase.cvtisr.sk/) was used to identify HGD gene variants. Of the patients, 37 (56.1%) presented with isolated dark urine and 29 (43.9%) were diagnosed based on the clinical symptoms or family screening. One of these patients was on follow-up for 2 years due to Parkinsonism and was diagnosed with AKU on further analyses. Signs of ochronosis such as joint pain, low back pain and renal stones developed in childhood in 7 patients. Eight patients were diagnosed with depression via psychiatric evaluation. There were 14 (21.2%) patients operated on for ochronosis. The most frequent mutation observed in the patients was c.175delA, which was followed by c.674G > A and c.1007-2A > T mutations. Four novel mutations (c.189G > A, c.549+1G > T, c.1188+1G > A, and c.334 T > G) were identified in the patients included in the study. In addition to the known signs such as dark urine and skin pigmentation, symptoms involving different systems such as neurological findings and depression can also be encountered in AKU patients. The presence of a change in urine color needs to be questioned in patients presenting with different symptoms such as arthralgia/arthritis, renal stones or low-back pain, particularly in childhood, when skin ochronosis is not pronounced, and further examination should be performed.

Homogentisic Acid-Based Whole-Cell Biosensor for Detection of Alkaptonuria Disease

Clinicians require simple quantitative tools for the detection of homogentisic acid in alkaptonuria patients, a rare inherited disorder of amino acid metabolism. In this study, we report a whole-cell biosensor for homogentisic acid to detect alkaptonuria disease through the expression of green fluorescence protein. The assay system utilizes a promoter sequence (hmgA) isolated from the Pseudomonas aeruginosa genome. To increase the sensitivity, the sensor module harboring phmgA::GFP was further transformed into various transposon mutants debilitated in steps involved in the metabolism of phenylalanine and tyrosine via homogentisic acid as a central intermediate. The proposed biosensor was further checked for analytical features such as sensitivity, selectivity, linearity, and precision for the quantification of homogentisic acid in spiked urine samples. The limit of detection for the developed biosensor was calculated to be 3.9 μM, which is comparable to that of the various analytical techniques currently in use. The sensor construct showed no interference from all of the amino acids and its homolog molecules. The accuracy and precision of the proposed biosensor were validated using high-performance liquid chromatography (HPLC) with satisfactory results.

Fatal acute haemolysis and methaemoglobinaemia in a man with renal failure and Alkaptonuria - Is nitisinone the solution?

Haemolysis and methaemoglobinaemia (MetHb) are rare metabolic complications that can occur in Alkaptonuria (AKU), for which there is no curative treatment. Presented is a case of a man who had AKU, and serves as a reminder of life-threatening complications that can occur with haemolysis and MetHb. This case presents an opportunity to revisit important considerations relating to the investigation and treatment of haemolysis and MetHb with a view to raising awareness, and in doing so hopefully reducing the uniformly fatal outcome. Additionally it is proposed that treatment of haemolysis and MetHb with nitisinone is considered as a potentially lifesaving treatment as it is believed that reducing the concentration of circulating homogentisic acid will reduce oxidative stress.