Musculoskeletal manifestations of alkaptonuria: A case report and literature review

Redefining a new frontier in alkaptonuria therapy with AI-driven drug candidate design via in- silico innovation

A rare metabolic condition called alkaptonuria (AKU) is caused by a decrease in homogentisate 1,2 dioxygenase (HGO) activity due to a mutation in homogentisate dioxygenase (HGD) gene. Homogentisic acid is a byproduct of the catabolism of tyrosine and phenylalanine that darkens the urine and accumulates in connective tissues which causes an agonizing arthritis. Employing the use of deep learning artificial intelligence (AI) drug design, this study aims to alleviate the current toxicity of the AKU drugs currently in use, particularly nitisinone, by utilizing the natural flavanol kaempferol molecule as a 4-hydroxyphenylpyruvate dioxygenase inhibitor. Kaempferol was employed to generate three effective de novo drug candidates targeting the enzyme 4-hydroxyphenylpyruvate dioxygenase using an AI drug design tool. We present novel AIK formulations in the present study. The AIK's (Artificial Intelligence Kaempferol) examination of drug-likeliness among the three led to its choice as a possible target. The toxicity assessment research of AIK demonstrates that it is not only safer to use than other treatments, but also more efficient. The docking of the AIGT with 4-hydroxyphenylpyruvate dioxygenase, which revealed a binding affinity of around -9.099 kcal/mol, highlights the AIK's potential as a therapeutic candidate. An innovative approach to deal with challenging circumstances is thus presented in this study by new formulations kaempferol that have been meticulously designed by AI. The results of the in vitro tests must be confirmed in vivo, even though AI-designed AIK is effective and sufficiently safe as computed.

Avulsive Achilles Tendon Rupture in a Patient With Alkaptonuria: A Case Report

Alkaptonuria is a rare autosomal recessive disease caused by a mutation in the homogentisate 1,2-dioxygenase (HGO) gene, leading to the accumulation of homogentisic acid (HGA). HGA polymerizes to form a black pigment that accumulates in connective tissue and joints (ochronosis), causing their destruction. In this work, we report a case of Achilles tendon rupture in a patient with a prior diagnosis of alkaptonuria. A 71-year-old man presented to the emergency department reporting pain in his posterior right ankle and dysfunction, evolving over three weeks after falling down a short flight of stairs. He had previously been diagnosed with alkaptonuria and had undergone five joint prostheses and an aortic valve replacement. A physical examination revealed right ankle edema, pain upon palpation, a palpable gap at the insertion of the tendon, and a positive Thompson test. An MRI confirmed an avulsive rupture at the insertion of the Achilles tendon. During surgical exploration, black pigmentation was observed in the tendon, which was reinserted using a double-row system reinforced with a percutaneous Bunnel stitch. The patient was discharged the following day with a cast splint, maintaining the foot in physiological plantar flexion for two weeks. In the subsequent two weeks, he used a non-weight-bearing walker boot, and finally, in the following two weeks, he began weight-bearing. Two months post-operation, he was walking without support. Twelve months after the intervention, the patient regained their previous functional status, being able to walk on tiptoes without difficulty. Spontaneous Achilles tendon rupture without associated trauma in patients with ochronosis is rare, with limited literature demonstrating successful outcomes post-surgery. Since the tendon becomes more fragile due to pigment accumulation, it was reinserted using a double-row system, increasing the contact area and more effectively distributing the load. There is no standard technique for treating these patients, but the patient's previous functional capacity was restored, with no new ruptures to date. The significant morbidity of alkaptonuria and potential complications, such as tendon ruptures, warrant future studies to discover and develop new prophylactic and therapeutic treatments.

Arthroplasty in Ochronotic Arthropathy: 3 Replacements in a Single Patient with a Long-term Follow-up of 11 Years

Introduction

Alkaptonuria is a rare autosomal recessive disorder caused by the defective metabolism of homogentisic acid, with a rare course and remained undetected even until adulthood. Ochronotic arthropathy is one of the manifestations of alkaptonuria, predominantly affecting weight bearing joints such as spine, hip, and knee. Total joint arthroplasty is treatment of choice in end-stage arthritis of hip and knee. Owing to the rarity of the disease, limited data is available in literature regarding surgical challenges and long-term functional outcomes.

Case Report

Herein, we present a case of 43-year-old male with ochronotic arthropathy of bilateral hip, right knee, and bilateral elbow joints with involvement of spine, who was incidentally diagnosed with ochronotic arthropathy intraoperatively and underwent sequential arthroplasty for right hip followed by right knee and left hip over a period of 10 years. At 11 years' follow-up, the patient has full mobility with no loosening of implants.

Conclusion

The long-term results of total joint arthroplasty in ochronotic arthropathy are good. Surgeon should be aware of the difficulty in soft tissue balancing and possible complications in the ochronotic arthropathy and require a conscientious approach to avoid complications.

Alkaptonuria in an Elderly Presenting with Asynchronous Rupture of both Quadriceps Tendons and Chronic Kidney Failure: Case Report and Literature Review

Introduction

Alkaptonuria (AKU) is a rare autosomal-recessive multisystemic disease. It is caused by a mutant homogentisate dioxygenase coding gene, leading to the accumulation of homogentisic acid (HGA), hence systemic manifestations. Renal manifestations and tendon rupture are rarely reported.

Case Report

We report a 60-year-old male with chronic kidney disease for over a decade who was initially misdiagnosed with ankylosing spondylitis and rheumatoid arthritis. Later on, the patient presented to our institute with a non-synchronized (8 years) acute quadriceps tendon rupture.

Conclusion

Physicians should be aware of the importance of prophylactic measures in the management of AKU, which is mainly medical management, to reduce the accumulation of HGA in the body. We further emphasize this point to reduce the incidence of subsequent tendon ruptures, as it significantly affects the quality of life.

Detection of homogentisic acid by electrospray ionization mass spectrometry

OBJECTIVE

Homogentisic acid (HGA) is excreted in excessive amounts in the urine of patients with alkaptonuria, which is a hereditary metabolic disorder of phenylalanine and tyrosine. Therefore, the detection of HGA in urine is useful for the diagnosis of alkaptonuria. To evaluate the detection of HGA, we confirmed the color shift of HGA solutions and analyzed them by electrospray ionization mass spectrometry (ESI-MS).

METHODS

We observed the color change of the HGA solutions under different pH conditions (pH 6.0, 7.0, and 8.0) and examined the influences of adding potassium hydroxide (KOH) and ascorbic acid (AA) to the HGA solutions. Then, we analyzed the chemical reaction in HGA solutions using ESI-MS.

RESULTS

The HGA solution at pH 8.0 became brown after incubation at room temperature for 24 h and became darker brown with the addition of KOH; however, HGA solutions at pH 6.0 and 7.0 showed no color changes. The brown color change of the HGA solution at pH 8.0 was also inhibited by AA. Moreover, all HGA sample solutions showed the deprotonated molecular ion peak at m/z 167.035 in the negative ion mode after incubation at room temperature for 24 h and with the addition of KOH and AA.

CONCLUSION

We identified the molecular ion of HGA in all sample solutions by ESI-MS, regardless of different pH conditions, color changes, or the presence of AA. These results suggest that spectral analysis by ESI-MS is suitable for the detection of HGA and the diagnosis of alkaptonuria.

Alkaptonuria Diagnosis Following a Discectomy: A Case Report

Alkaptonuria is a rare genetic disorder characterized by the excessive production of homogentisic acid, leading to the formation and deposition of pigment polymers throughout the body. It is extremely rare, affecting only around one in 100,000 individuals. Despite the normal life expectancy, it can cause severe morbidities. Alkaptonuria is typically managed supportively with pain medication, dietary modifications, and surgical interventions, which are considered to be the gold standard of therapy. Here we present a case of a 33-year-old male with no previous medical or surgical history who presented with severe acute back pain radiating to the left leg. Genetic testing confirmed a homozygous pathogenic variant for alkaptonuria. This case highlights the challenges in diagnosing alkaptonuria, emphasizing the significance of early detection, and clinical evaluation for improved outcomes. Furthermore, it underscores the need to consider alkaptonuria as a multidimensional disease, necessitating further research to enhance our understanding and develop effective management. Therefore, this study serves as an opportunity for future trials and studies aimed at digging deeper into the intricacies of alkaptonuria to increase our understanding and establish comprehensive management plans for affected individuals.

Bacterial quality of urinary tract in patients with alkaptonuria

BACKGROUND

The aim of the current study was to determine whether there is an association between alkaptonuria (AKU) and urinary tract infection (UTI) by exploring the bacterial quality of the urinary tract, as most of the patients with AKU present with frequent occurrence of urinary tract symptoms such as incomplete emptying of urinary bladder, dysuria and nocturia.

METHODS

Study samples were collected from 22 participants; 9 from patients with AKU, 9 from individuals who were AKU carriers, and 4 people served as control. Confirmation of AKU diagnosis was established by the ferric chloride test and quantitative determination of urinary homogentisic acid (HGA) levels.

RESULTS

In the ferric chloride test, the urine samples of AKU patients showed a characteristic black ring upon addition of few drops of ferric chloride solution. During urinary HGA determination, patients with AKU had increased levels of urinary HGA as compared to carriers and controls. The following 10 bacterial species were isolated from the urinary tract of AKU patients, carriers and controls: Sphingomonas paucimobilis, Escherichia coli, Francisella tularensis, Staphylococcus hominis, Staphylococcus haemolyticus, Leuconostoc mesenteroides, Dermacoccus nishinomiyaensis, Kytococcus sedentarius, Serratia fonticola and Granulicatella adiacens. The presence of S. paucimobilis was found in three male patients, and one female each from the carrier and control groups. Almost all study samples were positive for D. nishinomiyaensis and K. sedentarius. S. fonticola and G. adiacens were found only in AKU carrier females.

CONCLUSIONS

The results deduced that males show symptoms of arthritis early and more severely than females and by this it appears that there is an association between these symptoms and the percentage of bacterial infection in males that requires more accurate diagnosis and treatment to clarify such relationship. In the current study, males (patients, carriers, and controls) were more likely to have bacterial infections than females (64% vs. 36%). The 16 and 2 bacterial isolates, detected in 7 males and 2 females AKU patients, respectively, revealed that male AKU patients had a 2.3-fold greater rate of bacterial infection than female AKU patients. Therefore, further studies are warranted to investigate if there's any relationship between higher incidence of bacterial infections and development of AKU-related clinical symptoms in the male population.

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.

Ipsilateral hip and knee joints ochronotic arthropathy treated by total joint replacement, a case report

Background

Ochronotic arthropathy affecting the hip and knee joints is one of the musculoskeletal manifestations of alkaptonuria which results from a tyrosine amino acid metabolism disorder. The condition has no definitive management; however, end-stage joint arthritis is well treated by total joint replacement.

Case presentation

We present a case of a healthy male patient who presented with left hip and bilateral knee (more on the left side) progressive pain and limitation of motion how was diagnosed as having advanced arthritis and was treated by total hip and total knee replacement for the left hip and knee joints respectively. Intraoperatively, the tissues had blackish discoloration characterizing ochronosis. This patient was diagnosed as having ochronotic arthropathy based on the intraoperative findings.

Conclusions

Accurate diagnosis of ochronotic arthropathy could only be reached intraoperatively; furthermore, end-stage joint arthritis could be treated efficiently by total joint replacement surgery.

Ochronotic arthropathy in the context of spondyloarthritis differential diagnosis: a case-based review

Alkaptonuria is a disease often forgotten because of its rarity. Its pathogenic mechanism is the deficiency of one of the enzymes of the tyrosine degradation pathway-homogentisate-1, 2-dioxygenase, which sequelae is accumulation and deposition of its metabolite homogentisic acid in connective tissues and urine. Alkaptonuria presents as a clinical triad-darkening urine upon prolonged exposure to air, pigmentation of connective tissues and debilitating arthropathy. We present a case report of a 67-year old patient with alkaptonuria who presented with the clinical triad, but was mistakenly diagnosed as having ankylosing spondylitis in the past. Currently there is no treatment for the disease hence the management strategy was focused on symptoms control with analgesics, physical therapy, dietary modification, vitamin C supplementation, and joint arthroplasty. Alkaptonuria's clinical features are extensively described in the literature and despite the fact that it is a rare disease, due to the similar radiographic changes with spondyloarthropathies, it should be included in the differential diagnosis in young patients presenting with severe joint involvement. Early recognition of the disease is necessary since its natural evolution is joint destruction leading to significant reduction in the quality of life. Alkaptonuria's articular features in the spine and peripheral tissues are well described using the classical imaging techniques. Musculoskeletal ultrasonography shows a characteristic set of findings in the soft tissues, including synovium, cartilage, tendons and entheses.

Total knee replacement for ochronotic arthritis: A rare case report

Introduction and importance

Total knee replacement (TKR) is commonly performed for managing advanced osteoarthritis. There are several causative factors of osteoarthritis, from degenerative processes associated with age to rare genetic disorders correlated with a rare course of disease and remained undetected even until adulthood. Herein, we present a case of ochronotic arthritis characterized by black discoloration of the articular cartilage, meniscus, and soft tissue surrounding the right knee, which was detected during TKR, in a patient with alkaptonuria. This is a rare case and managing the patient require conscientious approach.

Case presentation

For the past four years, a 64-year-old man had been experiencing chronic right knee pain. During admission, the patient was limping and unable to bear weight on the affected knee. The right knee was swollen, with limited range of motion and audible crepitation during flexion. Radiography revealed narrowing of the joint space and osteophytes on the articular surface. Further investigation showed that the patient was previously diagnosed with alkaptonuria and was scheduled for TKR. Intraoperatively, we found that the articular cartilage, meniscal surface, and soft tissue surrounding the knee had black discoloration. Thus, additional debridement of soft tissues was required.

Clinical discussion

Alkaptonuria may increase the risk of osteoarthritis in the knee joint. Ochronosis correlated with alkaptonuria. Diagnosis can be conducted with physical examination, synovial fluid exam and complete urinalysis to avoid misdiagnose of this disease.

Conclusion

In our study, TKR for ochronotic arthritis had good outcomes, with a knee score of 95 and a function score of 90. The patient received routine treatment for alkaptonuria at the Urology Department.

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Alkaptonuria result in the accumulation of homogentisic acid in collagenous structure.

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Articular cartilage may experience mild discoloration due to deposition of hemosiderin and lipofuscin.

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Degenerative process result in joint arthrosis or pain, and reduced range of motion in the affected joint.

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TKR for ochronotic arthritis had good outcomes.

Whole exome sequencing reveals potentially pathogenic variants in a small subset of premenopausal women with idiopathic osteoporosis

Osteoporosis in premenopausal women with intact gonadal function and no known secondary cause of bone loss is termed idiopathic osteoporosis (IOP). Women with IOP diagnosed in adulthood have profound bone structural deficits and often report adult and childhood fractures, and family history of osteoporosis. Some have very low bone formation rates (BFR/BS) suggesting osteoblast dysfunction. These features led us to investigate potential genetic etiologies of bone fragility. In 75 IOP women (aged 20-49) with low trauma fractures and/or very low BMD who had undergone transiliac bone biopsies, we performed Whole Exome Sequencing (WES) using our variant analysis pipeline to select candidate rare and novel variants likely to affect known disease genes. We ran rare-variant burden analyses on all genes individually and on phenotypically-relevant gene sets. For particular genes implicated in osteoporosis, we also assessed the frequency of all (including common) variants in subjects versus 6540 non-comorbid female controls. The variant analysis pipeline identified 4 women with 4 heterozygous variants in LRP5 and PLS3 that were considered to contribute to osteoporosis. All 4 women had adult fractures, and 3 women also had multiple fractures, childhood fractures and a family history of osteoporosis. Two women presented during pregnancy/lactation. In an additional 4 subjects, 4 different relevant Variants of Uncertain Significance (VUS) were detected in the genes FKBP10, SLC34A3, and HGD. Of the subjects with VUS, 2 had multiple adult fractures, childhood fractures, and presented during pregnancy/lactation, and 2 had nephrolithiasis. BFR/BS varied among the 8 subjects with identified variants; BFR/BS was quite low in those with variants that are likely to have adverse effects on bone formation. The analysis pipeline did not discover candidate variants in COL1A1, COL1A2, WNT, or ALPL. Although we found several novel and rare variants in LRP5, cases did not have an increased burden of common LRP5 variants compared to controls. Cohort-wide collapsing analysis did not reveal any novel disease genes with genome-wide significance for qualifying variants between controls and our 75 cases. In summary, WES revealed likely pathogenic variants or relevant VUS in 8 (11%) of 75 women with IOP. Notably, the genetic variants identified were consistent with the affected women's diagnostic evaluations that revealed histological evidence of low BFR/BS or biochemical evidence of increased bone resorption and urinary calcium excretion. These results, and the fact that the majority of the women had no identifiable genetic etiology, also suggest that the pathogenesis of and mechanisms leading to osteoporosis in this cohort are heterogeneous. Future research is necessary to identify both new genetic and non-genetic etiologies of early-onset osteoporosis.

Treatment of osteoporotic fractures in alkaptonuria by teriparatide stimulates bone formation and decreases fracture rate - A report of two cases

Two cases of advanced alkaptonuria (AKU) with co-existing osteoporosis are described. Case 1 developed multiple non-vertebral fragility fractures, while Case 2 developed vertebral fragility fractures, both refractory to bisphosphonates. Difficulties in diagnosing osteoporosis in AKU complicated by extensive calcifying and ossifying spondylosis are discussed. Both patients continued to fracture despite nitisinone therapy for metabolic control of AKU, as well as bisphosphonate antiresorptive therapy for osteoporosis. Subsequently the patients were treated with teriparatide 20 μg subcutaneous injections daily for two years, leading to reduction in fractures soon after commencing therapy in both cases. Markers of bone remodelling P1NP and CTX were stimulated. No complications due hypercalcaemia or calcification were encountered in either case. We conclude that teriparatide is an effective adjunct in the treatment of AKU when bisphosphonates prove ineffective.

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Two case of osteoporosis are described in patients with the ultra-rare genetic disorder, Alkaptonuria (AKU)

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Diagnosis of osteoporosis in AKU is complicated by extensive calcifying and ossifying spondylosis

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Treatment of AKU with Nitisinone and or antiresorptive did not improve bone health in these patients

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Teriparatide led to a reduction in fractures and is an effective adjunct in AKU when bisphosphonates prove ineffective

Clinical and Surgical Insights on Bilateral Total Knee Arthroplasty in Ochronotic Arthropathy: A Case-based Review

Introduction

Ochronotic arthropathy (OcA) is a consequence of alkaptonuria, a rare systemic-inherited metabolic disorder leading to accumulation of homogentisic acid in articular cartilage and subsequent early degeneration of the joints. Only few cases of OcA managed with bilateral total knee arthroplasty (TKA) has been described in the literature so far. We aim to discuss surgical pearls, pitfalls, and clinical outcome of OcA of knees managed with simultaneous bilateral TKA.

Case Presentation

The patient was a 52-year-old female presented to outpatient facility with severe bilateral knee pain and difficult ambulation. After clinical and radiological diagnosis of osteoarthritis, she was posted for bilateral TKA. During arthrotomy, blackening of articular cartilage, quadriceps and patellar tendon, and synovium was noted. Subchondral bone was free of pigmentation though, seemed osteopenic while taking bone cuts. Right knee was implanted with cruciate retaining components with ultracongruent insert; while on the left side, posterior stabilized components were used. Diagnosis of ochronosis was made retrospectively with characteristic subtle pigmentation of nails, palms, pinnae, and urine homogentisic levels. Two years follow-up of the patient remained satisfactory without any major complications.

Conclusion

OcA may present with intra-operative surprise to the surgeon if not anticipated preoperatively. Simultaneous bilateral TKA is safe and effective treatment for end-stage arthritis. However, it is difficult to diagnose it preoperatively; a high clinical suspicion leads to meticulous assessment and counseling regarding potential anesthetic concerns, choice of implant, and possible intra-operative and post-operative complications reported sporadically though.

Alkaptonuria with extensive ochronotic degeneration of the Achilles tendon and its surgical treatment: a case report and literature review

Background

Alkaptonuria is a rare genetic metabolic disorder due to deficiency of homogentisate 1,2-dioxygenase (HGD), an enzyme catalyzing the conversion of homogentisate to 4-maleylacetoacetate in the pathway for the catabolism of phenylalanine and tyrosine. HGD deficiency results in accumulation of homogentisic acid and its pigmented polymer. Ochronosis is a bluish-black discoloration due to the deposition of the polymer in collagenous tissues. Extensive ochronotic involvement of the Achilles tendon in alkaptonuria and its surgical treatment is rarely reported.

Case report

A 43-year-old man presented to our clinic in March 2019 with sudden onset of left Achilles tendon pain with no history of prior trauma. Surgical exploration revealed a complete disruption of the tendon at its attachment to the calcaneus. Black pigmentation was extensive and reached the calcaneal tuberosity, extending about 7 cm from the insertion.

Discussion

Achilles reconstruction was performed using flexor hallucis longus tendon transfer. The patient experienced uncomplicated healing with satisfactory functional results.

Conclusion

Orthopedic surgeons should be aware of the progressive nature of alkaptonuria. Extensive degenerative changes of the ruptured tendon should be suspected so that physicians can plan tendon repair and facilitate prompt surgical intervention.

Frequency, diagnosis, pathogenesis and management of osteoporosis in alkaptonuria: data analysis from the UK National Alkaptonuria Centre

Osteoporosis and fractures are common features of alkaptonuria.

INTRODUCTION

A large cohort of alkaptonuria (AKU) patients was studied to better recognise and characterise osteoporosis and fractures in AKU.

METHODS

Assessments including questionnaire analysis, DEXA and CT densitometry at the neck of femur (FN), total hip (TH) and lumbar spine (LS) were performed on patients at baseline when 2 mg nitisinone was commenced, and yearly thereafter. Blood and urine samples were collected for chemical measurement. CT BMD Z-scores were generated.

RESULTS

Between June 2007 and March 2020, 87 AKU patients attended the NAC. At baseline, there were 48 fractures in 39 patients. Prevalence of osteoporosis was 3.1 at FN, 10.8 at TH and 24.7% at LS respectively. Prevalence of fragility fractures was greatly increased at 44.8%. The group with fractures showed increased ochronosis scores (p < 0.05). CT LS showed an inverse relationship with fractures (R = - 0.28; p < 0.05). CT LS was significantly lower in the fracture group (p < 0.002). Following nitisinone only, CT FN and CT TH decreased significantly (p < 0.05 and 0.01 respectively). Following nitisinone plus antiresorptive therapy, CT FN, CT TH and CT LS all increased significantly (p < 0.05, 0.05 and 0.001 respectively). However, patients on nitisinone plus antiresorptive had more fractures than nitisinone and no-treatment groups (p < 0.05).

CONCLUSIONS

Osteopenia and fragility fractures are common in AKU.. Anti-resorptive therapy increased BMD in AKU without decreasing fragility fractures. Bone densitometry measurements by DXA are less reliable than quantitative CT at the LS in AKU.

A Mimic of Ankylosing Spondylitis, Ochronosis: Case Report and Review of the Literature

PURPOSE OF REVIEW

Ochronosis and alkaptonuria are manifestations of the same condition-a rare autosomal recessive disorder resulting from a constitutional lack of homogentisate 1,2-dioxygenase (HGD) with the consequent accumulation of homogentisic acid (HGA). In ochronosis, HGA undergoes autoxidation as well as enzymatic oxidation to form an ochronotic pigment that accumulates in cartilage and connective tissues. In the beginning, there is homogentisic aciduria and pigmentation of cartilages and other connective tissues. In later years, generalized osteoarthritis of the spine and large joints, termed ochronotic arthropathy, develops.

RECENT FINDINGS

The diagnosis is confirmed by quantitative measurement of HGA in urine and mutation analysis of the HGD gene. One of the differential diagnoses for the skin findings is exogenous ochronosis, a limited hyperpigmentation of skin caused by some chemicals. As for the lumbar spine findings, there can be radiographic similarities with ankylosing spondylitis (AS) including reduced intervertebral disc spaces and loss of lumbar lordosis; however, ochronosis will spare the sacroiliac joint, and the lumbar spine will show dense, wafer-like disk calcification with a vacuum disc phenomenon and broad syndesmophytes. Here, we present a case of a patient with probable ochronosis that was treated many years as ankylosing spondylitis without response, and we provide a review of the current literature on ochronosis pathogenesis, diagnosis, and treatment.

Inflammatory rheumatic diseases in patients with ochronotic arthropathy

BACKGROUND

Ochronotic arthropathy (OcA) refers to excessive homogentisic acid (HGA) deposition in the musculoskeletal system. Our current understanding of OcA is limited, as there are less than a thousand alkaptonuria (AKU) cases reported in the literature. Herein, we investigated the rheumatological manifestations of OcA in a group of adult AKU patients.

METHODS

Adult AKU patients with symptoms suggestive of OcA were included. Patients underwent a detailed rheumatological assessment. Laboratory testing, including autoantibodies and radiological investigations such as conventional X-rays, and magnetic resonance imaging (MRI) were performed.

RESULTS

Eight out of 12 (66%) patients had symptoms consistent with OcA. The median age at OcA symptoms was 36 (27-48) years, and the presenting symptom was back pain in 87.5% of the patients. All patients had chronic back pain, and three (37.5%) had an inflammatory type of pain character. Radiographic sacroiliitis based on X-rays was present in 2 (25%) cases. MRI of the sacroiliac joints documented bone marrow edema in five (62.5%), and spinal MRI identified corner inflammatory lesions in three patients (37.5%). One patient (12.5%) had rheumatoid arthritis. Extra-articular involvement, including enthesitis (n = 1; 12.5%), interstitial lung disease (n = 1; 12.5%), and scleritis (n = 1; 12.5%), was also noted.

CONCLUSION

The frequent occurrence of OcA-related inflammatory manifestations in our patients contradicts the conventional concept of OcA as a non-inflammatory disorder. The activation of inflammatory pathways, possibly by the HGA products, may responsible for this condition.Significance and innovationsAbout three-fourths of adult ochronotic arthropathy (OcA) patients in our group had associated inflammatory disease.OcA associated inflammatory diseases were showing a severe phenotypeNearly half of the OcA patients required early prosthesis operations compared to their healthy counterparts.

Narrowing of the dark valve: aortic stenosis in alkaptonuria

The commonest cardiac pathology in patients with alkaptonuria is aortic stenosis. Patients with alkaptonuria and aortic stenosis may remain asymptomatic until the 6th decade. Surgeons may have to deal with per-operative difficulties as alkaptonuria is a systemic disease. Proper preoperative planning is important. The mechanical valve prosthesis is advisable in a patient with alkaptonuria and aortic stenosis considering disease pathophysiology. We report a 70-year-old male diagnosed with alkaptonuria and aortic stenosis, who underwent aortic valve (mechanical valve prosthesis) and ascending aorta replacement.

Long-Term Outcomes of the Knee and Hip Arthroplasties in Patients with Alkaptonuria

Alkaptonuria is a rare autosomal recessive metabolic disorder. It is characterized by the accumulation of homogentisic acid in the body due to a lack of enzymes that degrade it. Over time, it results in joint degeneration and eventually leads to ochronosis. Ochronosis refers to bluish-black discoloration of connective and other tissues within the body. In this study, we present 5 distinct cases diagnosed with alkaptonuria. They have undergone 8 total joint replacement surgeries (4 hips and 4 knees) within 8 years (2010-2018). All patients had an excellent outcome over several years. The follow-up period ranged from 2 to 10 years. Although none of the presented cases had intraoperative or postoperative adverse sequelae, we must take care when dealing with patients with ochronotic arthropathy. They carry a higher risk of complications than other patients with osteoarthritis disease. These complications include fractures due to fragile bone quality, muscle or tendon rupture, joint instability, and anesthesia-related complications. Total joint arthroplasty is a valid and safe option in the management of hip and knee ochronotic arthropathy.

Family history of ochronotic arthropathy

Alkaptonuria is a rare autosomal-recessive disorder that produces accumulation of homogentisic acid in body fluids. The accumulation in collagen tissues, mainly in the joint cartilage, produces ochronotic arthropathy. We report two clinical cases of one brother and sister with alkaptonuria and ochronotic arthropathy diagnosed in old age. In the first case, the patient is diagnosed by musculoskeletal involvement with long-term low back pain with other associated manifestations that made this pathology suspected. In the second case, the patient comes due to osteoporosis and other associated fractures and with the family history and the rest of the clinic, the appropriate complementary tests were performed and the diagnosis is established. It is unknown if there is consanguinity in these patients between parents or ancestors. It is an infrequent pathology that is often diagnosed intraoperatively. Despite the poor efficacy of medical treatment, it would be advisable to make an early diagnosis to avoid accumulation of the pigment and accelerated joint destruction and deposition in other locations. Owing to its prevalence, it is difficult to find a significant number of patients to search for new treatments that are intended to correct the enzyme deficit and not only to modify the elimination.

Hip and knee replacement in patients with ochronosis: Clinical experience and literature review

Patients with alkaptonuria can present ochronotic degenerative arthropathy due to the accumulation of pigments in the cartilages. Ochronotic arthropathy initially affects the spine, then there is the involvement of the other large joints, with greater frequency of the knees. In this article we will present two patients with alkaptonuria who have been effectively treated with knee and hip replacement, comparing our experience with what is available in the literature.

Mechanisms involved in the unbalanced redox homeostasis in osteoblastic cellular model of Alkaptonuria

Alkaptonuria (AKU) is a rare metabolic disease correlated with the deficiency of homogentisate 1,2-dioxygenase and leading to an accumulation of the metabolite homogentisic acid (HGA) which can be subjected to oxidation and polymerization reactions. These events are considered a trigger for the induction of oxidative stress in AKU but, despite the large description of an altered redox status, the underlying pathogenetic processes are still unstudied. In the present study, we investigated the molecular mechanisms responsible for the oxidative damage present in an osteoblast-based cellular model of AKU. Bone, in fact, is largely affected in AKU patients: severe osteoclastic resorption, osteoporosis, even for pediatric cases, and an altered rate of remodeling biomarkers have been reported. In our AKU osteoblast cell model, we found a clear altered redox homeostasis, determined by elevated hydrogen peroxide (H₂O₂) levels and 4HNE protein adducts formation. These findings were correlated with increased NADPH oxidase (NOX) activity and altered mitochondrial respiration. In addition, we observed a decreased activity of superoxide dismutase (SOD) and reduced levels of thioredoxin (TRX) that parallel the decreased Nrf2-DNA binding. Overall, our results reveal that HGA is able to alter the cellular redox homeostasis by modulating the endogenous ROS production via NOX activation and mitochondrial dysfunctions and impair the cellular response mechanism. These findings can be useful for understanding the pathophysiology of AKU, not yet well studied in bones, but which is an important source of comorbidities that affect the life quality of the patients.

Long-term follow-up of bilateral hip and knee arthroplasty secondary to ochronotic arthropathy

Alkaptonuria is a rare metabolic disorder caused by the deficiency of homogentisic acid oxidase enzyme, which is responsible for eliminating homogentisic acid from the body through the renal system. Excessive accumulation of homogentisic acid leads to ochronosis and ochronotic arthritis. Owing to the rarity of the disease, long-term functional outcomes of joint replacements of the hips and knees in ochronosis arthropathy are unconfirmed, and only a limited number of case reports are available on this. We present a case of a 45-year-old man with ochronosis and advanced osteoarthritis of both the hips and knees. He underwent bilateral hip and knee replacements as staged procedures. At a follow-up of more than 12 years, the man had full mobility with no loosening of implants.

[Black knee-ochronotic alterations in alkaptonuria]

This article presents the case of a 53-year-old male patient born in Sri Lanka, who presented to the outpatient unit with the suspicion of empyema of the knee joint. Within the framework of knee arthroscopy, the diagnosis of ochronosis was made and later confirmed by histopathological biopsy. The alkaptonuria is caused by a homogentisate 1,2-dioxygenase deficiency and leads to an accumulation of homogentisic acid, a degradation product of tyrosine. This leads to the characteristic appearance of ochronosis with bluish-black deposits in the tissue (e.g. in connective tissue, sclera and ear cartilage) and a black coloration of the urine.