Aortic stenosis and vascular calcifications in alkaptonuria

Alkaptonuria: a rare disease with multiorgan manifestation and a long-awaited diagnosis

Alkaptonuria is a rare inherited disease resulting from a genetic variant leading to homogentisic acid accumulation in body tissues, causing a broad spectrum of symptoms. Our case involves a Caucasian male diagnosed in his 70s, who shares a constellation of symptoms and the diagnosis with his monozygotic twin brother. The symptoms include early-onset arthropathy, tendinopathy, osteopenia, discolouration of the auricular regions and fingers, scleral discolouration, secondary glaucoma, proteinuria, calcification of the mitral valve and black urethral and prostate stones. Additionally, the patient suffers from chronic cough, polyneuropathy and corpus cysts in the thoracic spine have been found. This case highlights the importance of holistic assessments, recognition of familial symptom patterns and early identification of key clinical indicators for rare disease diagnosis. It also underscores the challenge of differentiating rare symptomatic manifestations from those unrelated to alkaptonuria.

An anatomical investigation of alkaptonuria: Novel insights into ochronosis of cartilage and bone

Ochronotic pigmentation of connective tissue is the central pathological process in the rare metabolic disease alkaptonuria (AKU). Tissue pigmentation in AKU occurs due to unmetabolised homogentisic acid (HGA) in the circulation, caused by an enzyme deficiency in the liver. Ochronotic pigmentation, derived from HGA, has previously been reported and described in large joints obtained from arthroplasty surgeries, which typically have advanced disease. Many tissues that are affected by ochronosis are not accessible for study during life, including tissues subjected to early and mid-stage disease. Here, the opportunity arose to anatomically examine a 60-year-old AKU female body donor, allowing the investigation of previously understudied tissue, including those undergoing early-stage pathological changes. Dissection of fresh-frozen tissue was carried out and harvested tissues were fixed and examined histologically using H&E and Schmorl's stains to aid identification of ochronotic pigment. This work focusses on osteochondral tissues including extra-skeletal cartilage, viscera and eyes. Gross and histological images demonstrating pigmentation in the cartilage and perichondrium of the ear ossicles, tympanic membrane and the pubic symphysis fibrocartilaginous disc are described for the first time here. We also show the first examination of the temporomandibular joint, which macroscopically appeared unpigmented, with histological analysis of the fibrocartilaginous disc showing no pigmentation. Pigmentation of non-articular hyaline cartilage was observed in the respiratory tract, in both the hyaline cartilage and perichondrium, confirming previous findings. Within smaller joints, pigmentation of chondrons and the surrounding territorial matrix was observed, but was confined to calcified articular cartilage, and was not generally found in the hyaline articular cartilage. Dark pigmentation of the perichondrium adjacent to the articular surface was observed in numerous small joints. The calcified bone matrix was not pigmented but ochronosis was identified in a small fraction of trabecular osteocytes in the capitate and radius, with substantially more pigmented osteocytes observed in bone of the ear ossicles. Viscera examined were unpigmented. This anatomical examination of tissues from an AKU individual highlights that most osteochondral tissues are susceptible to HGA-derived pigmentation, including the ear ossicles which are the smallest bones in the body. Within joints, calcified cartilage and perichondrium appear to be the earliest affected tissues, but why this is the case is not understood. Furthermore, why the TMJ disc was unaffected by pigmentation is intriguing. The heterogenous appearance of pigmentation both within and between different tissues indicates that factors other than tissue type (i.e. cartilage, perichondrium) and matrix composition (i.e. collagen-rich, calcified) may affect the process of ochronosis, such as oxygen tension, loading patterns and tissue turnover. The effect of nitisinone treatment on the ochronotic disease state is considered, in this case 7 years of treatment, however comparisons could not be made to other cases due to inter-individual variability.

A rare differential diagnosis of aortic stenosis with a black aortic valve: A case report

BACKGROUND

Cardiac ochronosis, presenting as a rare manifestation of alkaptonuria, an autosomal recessive disorder, is characterised by black pigmentation of calcified cardiac valves and atherosclerotic plaques. We report an intraoperative dilemma on the discovery on the black aortic valve in a case of an old lady with degenerative calcific aortic stenosis.

CASE PRESENTATION

A 60-year-old lady was electively admitted for valve replacement with a bioprosthetic valve for severe aortic stenosis. She was symptomatic with complaints of headache and giddiness and had a pressure gradient of 113/17mmhg across the aortic valve. Intraoperatively, she was found to have cardiac ochronosis on the discovery of pigmented aortic intima extending to the valve leaflets and underwent valve replacement with a mechanical prosthetic valve. She was post-operatively evaluated for the same and diagnosed with alkaptonuria. Though the surgery went uneventful and the patient was discharged without any complication, she was advised to be on regular follow-up to assess valve gradients, paravalvular leaks and to monitor the disease progression.

CONCLUSION

The presented case sheds light on the rare cardiac manifestation of alkaptonuria. In the absence of definitive pre-operative diagnosis, intraoperative findings played a pivotal role in guiding the surgical approach and choice of prosthetic valve. The decision to use a mechanical valve was influenced by the potential risks associated with bioprosthetic valves in the setting of ochronosis. Ongoing follow-up and monitoring are essential to assess the durability of the chosen prosthetic valve and to manage any long-term consequences of the underlying metabolic condition.

Ease of sutureless aortic valve replacement in a patient with unexpected ochronosis: a case report

BACKGROUND

Alkaptonuria is a rare congenital metabolic disorder characterized by homogentisic acid accumulation in body cartilage and connective tissues due to a deficient homogentisic acid dioxygenase enzyme. This disorder manifests in various clinical symptoms, including spondyloarthropathy, ocular and dermal pigmentation, genitourinary tract obstruction by ochronosis stones, and cardiovascular system involvement. Cardiac ochronosis is a rare manifestation of alkaptonuria that may present as aortic stenosis, sometimes accompanied by other cardiovascular complications.

CASE PRESENTATION

We report an unexpected case of ochronosis diagnosed during cardiac surgery. Due to the fragile, thin, and atheromatous nature of the ascending aorta in patients with ochronosis, we opted for a sutureless aortic valve replacement procedure. This approach appears to be more suitable for patients with ochronosis.

CONCLUSIONS

Although cardiac ochronosis is rare, surgeons should remain vigilant and consider the possibility of this condition when examining patients with aortic valve stenosis, paying close attention to the clinical manifestations of alkaptonuria.

Insights into calcific aortic valve stenosis: a comprehensive overview of the disease and advancing treatment strategies

Aortic valve stenosis is a disease characterized by thickening and narrowing of the aortic valve (AV), most commonly due to calcification, which leads to left ventricular outflow obstruction called calcific aortic valve disease (CAVD). CAVD presents as a progressive clinical syndrome with cardiorespiratory symptoms, often with rapid deterioration. The modern-day pathophysiology of CAVD involves a complex interplay of genetic factors, chronic inflammation, lipid deposition, and valve calcification, with early CAVD stages resembling atherosclerosis. Various imaging modalities have been used to evaluate CAVD, with a recent trend of using advanced imaging to measure numerous AV parameters, such as peak jet velocity. Significant improvements in mortality have been achieved with transcatheter AV repair, but numerous therapeutics and modalities are being researched to delay the progression of CAVD. This article aims to provide a comprehensive review of CAVD, explore recent developments, and provide insights into future treatments with various novel modalities.

Alkaptonuria

Alkaptonuria is a rare inborn error of metabolism caused by the deficiency of homogentisate 1,2-dioxygenase activity. The consequent homogentisic acid (HGA) accumulation in body fluids and tissues leads to a multisystemic and highly debilitating disease whose main features are dark urine, ochronosis (HGA-derived pigment in collagen-rich connective tissues), and a painful and severe form of osteoarthropathy. Other clinical manifestations are extremely variable and include kidney and prostate stones, aortic stenosis, bone fractures, and tendon, ligament and/or muscle ruptures. As an autosomal recessive disorder, alkaptonuria affects men and women equally. Debilitating symptoms appear around the third decade of life, but a proper and timely diagnosis is often delayed due to their non-specific nature and a lack of knowledge among physicians. In later stages, patients' quality of life might be seriously compromised and further complicated by comorbidities. Thus, appropriate management of alkaptonuria requires a multidisciplinary approach, and periodic clinical evaluation is advised to monitor disease progression, complications and/or comorbidities, and to enable prompt intervention. Treatment options are patient-tailored and include a combination of medications, physical therapy and surgery. Current basic and clinical research focuses on improving patient management and developing innovative therapies and implementing precision medicine strategies.

Surgical management of calcific valvular and coronary disease in a patient with alkaptonuria: a case report

Background

Alkaptonuria is a rare metabolic disease that causes an increase in homogentisic acid (HGA) due to a lack of enzymatic activity. Commonly, accumulation of HGA presents with dark discoloration of skin and other tissues, also known as ochronosis. Additionally, alkaptonuria can result in other clinical manifestations, including arthritis and cardiac disease. This case highlights alkaptonuria-related cardiac disease and challenges that cardiac surgery teams may face when treating this patient population.

Case summary

A 62-year-old male with a history of alkaptonuria, Hodgkin's lymphoma treated with chemoradiation, hypertension, and hyperlipidaemia originally presented with shortness of breath in the setting of known cardiac disease. Cardiac work-up demonstrated aortic stenosis, mitral stenosis, and multivessel coronary artery disease requiring aortic valve replacement, mitral valve replacement, and coronary artery bypass grafting. During the operation, significant discoloration of tissue was observed. This correlated with areas of severe calcification, which was noted throughout both valves. Extensive debridement was required prior to proceeding to valve replacements. Additionally, near-infrared spectroscopy failed to provide accurate measurements of cerebral oxygenation.

Discussion

Alkaptonuria is correlated with cardiovascular disease, particularly valvular disease. Intraoperatively, these patients may exhibit noticeable discoloration and severe calcification of various tissues. Additionally, traditional infrared-based methods of cerebral oxygenation monitoring may not be reliable; however, other options of cerebral monitoring may be feasible. With proper pre-operative planning, however, patients with alkaptonuria may safely undergo cardiac surgery.

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.

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.

Ochronotic heart disease leading to severe aortic valve and coronary artery stenosis

Cardiac ochronosis is a rare disease, estimated to affect 1 in 250,000 persons. While there is extensive evidence of the musculoskeletal alterations of the disease, cardiac involvement has not been widely studied and most information we currently have derives from case reports and case series. We report the case of a 64-year old patient with a known history of alkaptonuria who presented with dyspnea and weight loss. On evaluation, he was found to have severe aortic stenosis, coronary artery disease, and interventricular septal hypertrophy. Surgery revealed extensive ochronotic pigment deposition affecting the cardiac septum, both internal thoracic arteries, the native coronary arteries, and the aortic valve. Ochronotic heart disease is an often disregarded presentation of alkaptonuria. More information is needed on the course of the disease, as well as long-term outcomes after valve replacement surgery and/or coronary artery bypass grafting in patients with alkaptonuria.

Clinical and biochemical footprints of inherited metabolic diseases. IV. Metabolic cardiovascular disease

Inherited metabolic diseases account for 15-20% of all cases of pediatric cardiomyopathy, with a high mortality of 15-47%. Metabolic diseases can also commonly be associated with other types of cardiovascular involvement such as arrhythmias, valvulopathy or vasculopathy. We reviewed and updated the list of known metabolic etiologies associated with cardiovascular involvement, and found 246 relevant inborn errors of metabolism. This represents the fourth of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

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.

Minimally invasive endoscopic aortic valve replacement for alkaptonuria-associated severe aortic stenosis: a case report and literature review

Alkaptonuria is an inherited metabolic disease caused by a genetic deficiency of homogentisate 1,2-dioxygenase and characterized by dark-brown connective tissue related to the deposition of oxidized homogentisic acid. Pigment deposition is also observed in the cardiovascular system, such as in the coronary arteries, cardiac valves, and aorta. Because aortic stenosis may develop secondary to pigment deposition-related calcification at the aortic valve, aortic valve replacement may be necessary for severe aortic valve disease. We report the case of a 75 year-old man with alkaptonuria-associated severe aortic stenosis who was successfully treated with minimally invasive endoscopic aortic valve replacement via right anterior minithoracotomy. The tricuspid aortic valve was severely calcified and both the valve and the aortic intima were ochronotic. No perioperative complications were observed and the postoperative course was uneventful.

Aortic distensibility in alkaptonuria

INTRODUCTION

Alkaptonuria (AKU) is a rare inherited disorder of tyrosine metabolism resulting in an accumulation of homogentisic acid oxidation products in the joints and cardiovascular system. Aortic distensibility may be a non-invasive indicator of cardiovascular complications. Descending thoracic aortic distensibility in alkaptonuria has not been studied.

METHODS

Patients diagnosed with alkaptonuria underwent Magnetic Resonance Imaging (MRI) and gated non-contrast and contrast-enhanced cardiovascular computed tomography. Using MRI cine images, aortic distensibility of the descending thoracic aorta was determined.

RESULTS

Seventy-six patients with alkaptonuria were imaged. When compared to literature normal values, aortic distensibility in AKU was impaired (5.2 vs 6.2 × 10^-3, p < .001). Aortic distensibility was inversely related to age (r = -0.6, p = .0001). Hypertensive patients with alkaptonuria had impaired distensibility compared to normotensive patients with alkaptonuria (4.6 vs 5.6 × 10^-3, p = .03), and hyperlipidemic patients with alkaptonuria had impaired distensibility compared to non-hyperlipidemic patients with alkaptonuria (4.1 vs 6.0 × 10^-3, p = .001). Male hypertensive patients with alkaptonuria had greater distensibility than their female counterparts (5.3 vs 2.9 × 10^-3, p = .02). Similarly, male hyperlipidemic patients with alkaptonuria had greater distensibility than their female counterparts (4.8 vs 2.5 × 10^-3, p < .01). Of patients with alkaptonuria, those with a coronary artery calcium (CAC) score greater than 100 had more impaired distensibility than those with a CAC score less than 100 (3.5 vs 5.1 × 10^-3, p = .01) and those with aortic calcium score greater than 100 had impaired distensibility compared to those with an aortic calcium score less than 100 (3.2 vs 4.9 × 10^-3, p = .02). Univariate analysis revealed age, aortic calcification, and hyperlipidemia to be significant factors of distensibility, and multiple regression analysis showed age as the only significant risk factor of distensibility.

CONCLUSIONS

Patients with alkaptonuria have impaired aortic distensibility, which is likely an early marker for reduced cardiovascular health. Variables such as age, hypertension, hyperlipidemia, and aortic and coronary calcification were associated with impaired distensibility.

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.

A patient survey on the impact of alkaptonuria symptoms as perceived by the patients and their experiences of receiving diagnosis and care

BACKGROUND

Alkaptonuria (AKU) is an ultrarare and multifaceted disease characterized by the absence of functional homogentisate 1,2-dioxygenase activity, the enzyme responsible for breakdown of homogentisic acid-a tyrosine-degradation product. The presymptomatic phase of the disease makes diagnosis difficult, with many patients unidentified or diagnosed late in life.

OBJECTIVE

To date, no study has analyzed the perceived impact of different symptoms or the experiences of individuals through the patient journey in the context of AKU. This study aimed to examine patients' perceptions of AKU symptoms and their impact on quality of life as well as patients' experiences of being diagnosed and living with the disease.

METHODS

Data for this study were collected using a quantitative self-report questionnaire administered online to people with AKU.

RESULTS

Data from 45 participants indicate that symptoms with the highest impact for patients are those related to pain and ruptures, disability and inability to perform normal routines, emotional/mental health issues, and heart complications. Findings also revealed significant delays in contact with healthcare services and time to diagnosis. Furthermore, patients reported difficulty in receiving information about AKU, treatment and care, and long-term disease management support.

CONCLUSIONS

Time to diagnosis and care of AKU is significantly delayed. Symptoms of AKU with the highest impact on quality of life for patients are those related to pain and disability and the inability to perform normal routines. Bridging any gaps between patients with AKU and healthcare professionals through education could help improve patients' experiences with AKU through the patient journey.

Alkaptonuric ochronosis of the carotid artery

Alkaptonuria is a rare autosomal-recessive metabolic disorder of tyrosine degradation which results in elevated levels of circulating homogentisic acid. Ochronosis occurs when homogentisic acid polymerizes and deposits in connective tissue. Ochronotic lesions in the carotid arteries have not been described. In this report, we describe a 65-year-old man with alkaptonuria, with hypertension and hyperlipidemia, who underwent an uneventful carotid endarterectomy for an asymptomatic high-grade internal carotid artery stenosis. Histology revealed homogentisic acid deposits as black-brownish areas in the intima. He was noted to have an impressive heavily brown-black pigmented discoloration of the carotid plaque. Cardiovascular involvement is a rare consequence of alkaptonuria and is manifested by pigment deposition at the areas influenced by shear stress and turbulence.

Conditional targeting in mice reveals that hepatic homogentisate 1,2-dioxygenase activity is essential in reducing circulating homogentisic acid and for effective therapy in the genetic disease alkaptonuria

Alkaptonuria is an inherited disease caused by homogentisate 1,2-dioxygenase (HGD) deficiency. Circulating homogentisic acid (HGA) is elevated and deposits in connective tissues as ochronotic pigment. In this study, we aimed to define developmental and adult HGD tissue expression and determine the location and amount of gene activity required to lower circulating HGA and rescue the alkaptonuria phenotype. We generated an alkaptonuria mouse model using a knockout-first design for the disruption of the HGD gene. Hgd tm1a -/- mice showed elevated HGA and ochronosis in adulthood. LacZ staining driven by the endogenous HGD promoter was localised to only liver parenchymal cells and kidney proximal tubules in adulthood, commencing at E12.5 and E15.5 respectively. Following removal of the gene trap cassette to obtain a normal mouse with a floxed 6th HGD exon, a double transgenic was then created with Mx1-Cre which conditionally deleted HGD in liver in a dose dependent manner. 20% of HGD mRNA remaining in liver did not rescue the disease, suggesting that we need more than 20% of liver HGD to correct the disease in gene therapy. Kidney HGD activity which remained intact reduced urinary HGA, most likely by increased absorption, but did not reduce plasma HGA nor did it prevent ochronosis. In addition, downstream metabolites of exogenous 13C6-HGA, were detected in heterozygous plasma, revealing that hepatocytes take up and metabolise HGA. This novel alkaptonuria mouse model demonstrated the importance of targeting liver for therapeutic intervention, supported by our observation that hepatocytes take up and metabolise HGA.

Ochronotic arthritis and ochronotic Achilles tendon rupture in alkaptonuria: A 6 years follow-up case report in China

INTRODUCTION

Alkaptonuria (AKU) is a rare disease caused by deficiency of homogentisate 1,2-dioxygenase which results in deposition of homogentisic acid (HGA). Ochronotic arthritis, the deposition of excess oxidized HGA in the connective tissues, causes pigmentation and degeneration of the joint tissues ultimately resulting in chronic inflammation and osteoarthritis. The ochronotic arthritis has similar clinical features with osteoarthritis. There is currently no specific treatment for AKU and management is usually symptomatic. In severe cases, total joint arthroplasty is the major treatment approaches. It is rarely reported in China.

PATIENT CONCERNS

Here we reported a case of a patient with bilateral knee pain for more than 1 year. He complained of a 20-year history of chronic, nonspecific low back pain and stiffness. His urine was black since he was a child. Six years after the knee surgery, his Achilles tendon ruptured.

DIAGNOSIS

Specific radiographic and magnetic resonance imaging manifestations were observed. Darkly pigmented full-thickness cartilage and subchondral bone were found during the operation. Histological investigation also manifested dark stains in meniscus and synovial tissues. Black-denatured tendon tissue was also found during the operation. The patient was diagnosed as AKU.

INTERVENTIONS

Total knee arthroplasty and Achilles tendon repair were operated separately after the disease was diagnosed.

OUTCOMES

The patient recovered very well after the second surgery. He returned to full activities, described no knee pain, and presented to the clinic walking without any aid. Physical examination revealed 0 to 20 of plantar flexion and 0 to 15 of dorsiflexion of the ankle.

CONCLUSIONS

Ochronosis is a very rare disease in Asia. This paper supplies new information for study of this disease. The mechanism is still unknown right now. Further studies will be necessary.

[Anesthetic management of two patients with alkaptonuric ochronosis for total knee arthroplasty]

The current case report describes two cases of alkaptonuric ochronosis for anesthetic management. Alkaptonuria is a rare genetic orphan disease of tyrosine metabolism characterized by an accumulation of homogentisic acid in cartilage and connective tissues. Patients present most commonly for orthopedic joint surgery due to progressive arthropathy that can be misdiagnosed many a times. However respiratory, airway, cardiovascular and genitourinary systems complications can occur with age progressing. Restricted range of motion of cervical spine may lead to difficulty with airway management. In addition, degenerative changes and stiffness of lumbar spine due to ochronosis would make neuraxial blockade challenging. Although this inherited condition is extremely rare, anesthesiologists should be aware of its existence and prepare for management of potential challenging problems. This report highlights special care and precautions that need to be taken during anesthetic management.

Alkaptonuria-associated aortic stenosis

Alkaptonuria is an autosomal recessive disorder of tyrosine metabolism, which results in accumulation of unmetabolized homogentisic acid and its oxidized product in various tissues, including the heart. Cardiovascular involvement is a rare but serious complication of the disease. We present two patients who have undergone successful aortic valve replacement for alkaptonuria-associated aortic stenosis along with a review of the literature.

Aortic valve replacement for aortic stenosis caused by alkaptonuria

We report a case of aortic stenosis associated with ochronosis in a 70-year-old man who underwent biologic aortic valve replacement. Intraoperative findings included ochronosis of a severely calcified pigmented aortic valve along with pigmentation of the intima of the aorta.