Homogentisic acid is not only eliminated by glomerular filtration and tubular secretion but also produced in the kidney in alkaptonuria.

The clinical effects of alkaptonuria (AKU) are delayed and ageing influences disease progression. Morbidity of AKU is secondary to high circulating homogentisic acid (HGA) and ochronosis. It is not known whether HGA is produced by or processed in the kidney in AKU. Data from AKU patients from four studies were merged to form a single AKU group. A control group of non-AKU subjects was generated by merging data from two non-AKU studies. Data were used to derive renal clearance and fractional excretion (FE) ratios for creatinine, HGA, phenylalanine (PHE) and tyrosine (TYR) using standard calculations, for comparison between the AKU and the control groups. There were 225 AKU patients in the AKU group and 52 in the non-AKU control group. Circulating HGA increased with age (P < 0.001), and was significantly associated with decreased HGA clearance (CLHGA ) (P < 0.001) and FEHGA (P < 0.001). CLHGA and FEHGA were increased beyond the theoretical maximum renal plasma flow, confirming renal production and emphasising the greater contribution of net tubular secretion than glomerular filtration to renal elimination of HGA. The kidneys are crucial to elimination of HGA. Elimination of HGA is impaired with age resulting in worsening disease over time. The kidney is an important site for production of HGA. Tubular secretion of HGA contributes more to elimination of HGA in AKU than glomerular filtration.

ARTHROPLASTY IN ALKAPTONURIC OCHRONOSIS.

Ochronotic degenerative arthropathy occurs in patients with alkaptonuria. Alkaptonuria disorder is an extremely rare disease characterized by black pigmentation of various tissues (e.g., cartilage and connective tissue). Ochronotic arthropathy is a disabling disease that primarily affects the large joints. Like other metabolic diseases that involve the musculoskeletal system, care must be taken with regard to the quality of the affected bones, tendons and ligaments, and therefore the stability and survival of joint prosthesis. The following is a report of a 66-year-old man affected by several musculoskeletal manifestations of alkaptonuria with severe joints disruption, who was successfully treated with total left hip and total right knee replacements. Surgical, anesthesiological and postoperative management of these patients may require more vigilance due to the associated comorbidities of this disorder.

Anesthetic management of two patients with alkaptonuric ochronosis for total knee arthroplasty / Manejo anestésico de dois pacientes com ocronose alcaptonúrica para artroplastia total do joelho

Abstract 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.

Resumo Este relato descreve o manejo anestésico em dois casos de ocronose alcaptonúrica. Alcaptonúria é uma doença genética rara do metabolismo de tirosina caracterizada por acúmulo de ácido homogentísico em cartilagem e tecidos conjuntivos. Os pacientes geralmente recorrem à cirurgia ortopédica devido à artropatia progressiva, que, muitas vezes, pode ser diagnosticada incorretamente. No entanto, complicações das vias respiratórias, cardiovasculares e geniturinárias podem ocorrer com o avanço da idade. A restrição de mobilidade da coluna cervical pode levar ao manejo difícil das vias aéreas. Além disso, as alterações degenerativas e a rigidez da coluna lombar devido à ocronose podem tornar o bloqueio neuroaxial um desafio. Embora essa condição hereditária seja extremamente rara, os anestesiologistas devem estar cientes de sua existência e se preparar para o manejo de potenciais problemas desafiadores. Este relato destaca os cuidados e as precauções especiais que devem ser tomadas durante o manejo anestésico.

Tyrosinase, could it be a missing link in ochronosis in alkaptonuria?

The hypothesis that is proposed is that tyrosinase, an enzyme widely found within the human body is implicated in the ochronosis that occurs in alkaptonuria; an autosomal recessive condition first used by Archibald Garrod to describe the theory of "Inborn Errors of Metabolism." The disease results from the absence of a single enzyme in the liver that breaks down homogentisic acid; this molecule becomes systemically elevated in sufferers. The condition is characterised by a clinical triad of symptoms; homogentisic aciduria from birth, ochronosis (darkening) of collagenous tissues (from ∼30years of age) and ochronotic osteoarthropathy in weight bearing joints due to long term ochronosis in them (from ∼40years of age). Tyrosinase, a polyphenol oxidase has been shown in many species to contribute to the darkening of tissues in many organisms; including humans in the production of melanin. Tyrosinase under the right conditions shows alterations in its substrate specificity and may contribute to the darkening seen in AKU where it moves away from polymerising tyrosine but also homogentisic acid, the causative molecule in alkaptonuria, that is present in excess.

Alkaptonuria: An example of a "fundamental disease"--A rare disease with important lessons for more common disorders.

"Fundamental diseases" is a term introduced by the charity Findacure to describe rare genetic disorders that are gateways to understanding common conditions and human physiology. The concept that rare diseases have important lessons for biomedical science has been recognised by some of the great figures in the history of medical research, including Harvey, Bateson and Garrod. Here we describe some of the recently discovered lessons from the study of the iconic genetic disease alkaptonuria (AKU), which have shed new light on understanding the pathogenesis of osteoarthritis. In AKU, ochronotic pigment is deposited in cartilage when collagen fibrils become susceptible to attack by homogentisic acid (HGA). When HGA binds to collagen, cartilage matrix becomes stiffened, resulting in the aberrant transmission of loading to underlying subchondral bone. Aberrant loading leads to the formation of pathophysiological structures including trabecular excrescences and high density mineralised protrusions (HDMPs). These structures initially identified in AKU have subsequently been found in more common osteoarthritis and appear to play a role in joint destruction in both diseases.

Oxidative stress and mechanisms of ochronosis in alkaptonuria.

Alkaptonuria (AKU) is a rare metabolic disease due to a deficient activity of the enzyme homogentisate 1,2-dioxygenase (HGD), involved in Phe and Tyr catabolism. Due to such a deficiency, AKU patients undergo accumulation of the metabolite homogentisic acid (HGA), which is prone to oxidation/polymerization reactions causing the production of a melanin-like pigment. Once the pigment is deposited onto connective tissues (mainly in joints, spine, and cardiac valves), a classical bluish-brown discoloration is imparted, leading to a phenomenon known as "ochronosis", the hallmark of AKU. A clarification of the molecular mechanisms for the production and deposition of the ochronotic pigment in AKU started only recently with a range of in vitro and ex vivo human models used for the study of HGA-induced effects. Thanks to redox-proteomic analyses, it was found that HGA could induce significant oxidation of a number of serum and chondrocyte proteins. Further investigations allowed highlighting how HGA-induced proteome alteration, lipid peroxidation, thiol depletion, and amyloid production could contribute to oxidative stress generation and protein oxidation in AKU. This review briefly summarizes the most recent findings on HGA-induced oxidative stress in AKU, helping in the clarification of the molecular mechanisms of ochronosis and potentially providing the basis for its pharmacological treatment. Future work should be undertaken in order to validate in vivo the results so far obtained in in vitro AKU models.

Ochronotic osteoarthropathy in a mouse model of alkaptonuria, and its inhibition by nitisinone.

BACKGROUND: Alkaptonuria (AKU) is a rare metabolic disease caused by deficiency of homogentisate 1,2 dioxygenase, an enzyme involved in tyrosine catabolism, resulting in increased circulating homogentisic acid (HGA). Over time HGA is progressively deposited as a polymer (termed ochronotic pigment) in collagenous tissues, especially the cartilages of weight bearing joints, leading to severe joint disease. OBJECTIVES: To characterise blood biochemistry and arthropathy in the AKU mouse model (Hgd-/-). To examine the therapeutic effect of long-term treatment with nitisinone, a potent inhibitor of the enzyme that produces HGA. METHODS: Lifetime levels of plasma HGA from AKU mice were measured by high-performance liquid chromatography (HPLC). Histological sections of the knee joint were examined for pigmentation. The effect of nitisinone treatment in both tissues was examined. RESULTS: Mean (±SE) plasma HGA levels were 3- to 4-fold higher (0.148±0.019 mM) than those recorded in human AKU. Chondrocyte pigmentation within the articular cartilage was first observed at 15 weeks, and found to increase steadily with mouse age. Nitisinone treatment reduced plasma HGA in AKU mice throughout their lifetime, and completely prevented pigment deposition. CONCLUSIONS: The AKU mouse was established as a model of both the plasma biochemistry of AKU and its associated arthropathy. Early-stage treatment of AKU patients with nitisinone could prevent the development of associated joint arthropathies. The cellular pathology of ochronosis in AKU mice is identical to that observed in early human ochronosis and thus is a model in which the early stages of joint pathology can be studied and novel interventions evaluated.

Total knee arthroplasty in ochronosis: a case report and critical review of the literature.

Alkaptonuria is an autosomal recessive disorder caused by the deficiency of homogentisate 1.2 dioxygenase activity. The clinical presentation shows an ochronotic pigment which is deposited in all connective tissues, including in cartilage, particularly. The knee is the most common site of peripheral abnormality. There is currently no definitive cure for alkaptonuric ochronosis. In this article, we present a 69-year-old male case who underwent bilateral cemented total knee arthroplasty simultaneously. Our results during two-year follow-up were satisfactory. A critical review of the literature revealed no uniformity in reporting such cases.

The role of calcified cartilage and subchondral bone in the initiation and progression of ochronotic arthropathy in alkaptonuria.

OBJECTIVE: Alkaptonuria is a genetic disorder of tyrosine metabolism, resulting in elevated circulating concentrations of homogentisic acid. Homogentisic acid is deposited as a polymer, termed ochronotic pigment, in collagenous tissues, especially cartilages of weight-bearing joints, leading to a severe osteoarthropathy. We undertook this study to investigate the initiation and progression of ochronosis from the earliest detection of pigment through complete joint failure. METHODS: Nine joint samples with varying severities of ochronosis were obtained from alkaptonuria patients undergoing surgery and compared to joint samples obtained from osteoarthritis (OA) patients. Samples were analyzed by light and fluorescence microscopy, 3-dimensional scanning electron microscopy (SEM), and the quantitative backscattered electron mode of SEM. Cartilage samples were mechanically tested by compression to determine Young's modulus of pigmented, nonpigmented, and OA cartilage samples. RESULTS: In alkaptonuria samples with the least advanced ochronosis, pigment was observed intracellularly and in the territorial matrix of individual chondrocytes at the boundary of the subchondral bone and calcified cartilage. In more advanced ochronosis, pigmentation was widespread throughout the hyaline cartilage in either granular composition or as blanket pigmentation in which there is complete and homogenous pigmentation of cartilage matrix. Once hyaline cartilage was extensively pigmented, there was aggressive osteoclastic resorption of the subchondral plate. Pigmented cartilage became impacted on less highly mineralized trabeculae and embedded in the marrow space. Pigmented cartilage samples were much stiffer than nonpigmented or OA cartilage as revealed by a significant difference in Young's modulus. CONCLUSION: Using alkaptonuria cartilage specimens with a wide spectrum of pigmentation, we have characterized the progression of ochronosis. Intact cartilage appears to be resistant to pigmentation but becomes susceptible following focal changes in calcified cartilage. Ochronosis spreads throughout the cartilage, altering the mechanical properties. In advanced ochronosis, there is aggressive resorption of the underlying calcified cartilage leading to an extraordinary phenotype in which there is complete loss of the subchondral plate. These findings should contribute to better understanding of cartilage-subchondral interactions in arthropathies.

Dermoscopic and reflectance confocal microscopic features of exogenous ochronosis.

BACKGROUND: Exogenous ochronosis presents as an acquired asymptomatic hyperpigmentation on photoexposed areas, predominantly over bony prominences, and is caused by the topical application of several skin-lightening agents. OBSERVATIONS: We describe a 63-year-old Hispanic woman who developed exogenous ochronosis lesions on her face after using topical bleaching creams containing hydroquinone, 2% to 3%, and oxybenzone, 2%, for several years. Dermoscopy revealed irregular brown-gray globular, annular, and arciform structures that corresponded to focal deposition of ochronotic pigment on the dermis. These deposits correlated with multiple banana-shaped nonrefractile structures seen using reflectance confocal microscopy. Histopathologic sections revealed the deposition of a banana-shaped, yellow to brown material in the papillary and middle dermis. Ultrastructural examination revealed an amorphous electron-dense material mostly located in the core of elastic fibers and also in smaller amounts in the interstitium with prominent degenerative changes in the elastic fibers. A good correlation was observed between the results of both noninvasive techniques and the diagnostic histologic features of this condition. CONCLUSIONS: We characterized by means of dermoscopy, reflectance confocal microscopy, and electronic microscopy a case of exogenous ochronosis. To our knowledge, this is the first description of reflectance confocal microscopic findings in this condition. Dermoscopy and reflectance confocal microscopy are proved to be useful noninvasive techniques for the diagnosis of this pigmentary disorder.

[Ochronotic spondylarthropathy]. / Okronotisk spondylartropati.

We describe a patient with ochronotic spondyloarthropathy who presented with severe spinal stiffness, advanced degenerative changes in the spine with ossifications of the intervertebral discs and subchondral sclerosis of the sacroiliac joints. The diagnosis of ochronosis was verified by detection of homogentisic acid in the urine. Ochronosis is rare, but should be kept in mind as a differential diagnosis to other spondyloarthropathies including AS.

Alkaptonuria and intramedullary calcification.

Alkaptonuria is a rare disorder of metabolism caused by deficiency of homogentisic acid oxidase enzyme and characterized by triad of homogentisic aciduria (dark urine), relentlessly progressive arthritis and ochronosis. We have documented a case with typical features of alkaptonuria along with intramedullary calcification which has not been reported in the literature before.

Ochronosis and lumbar disc herniation.

Alkaptonuria is a rare, autosomal recessive metabolic disorder in which the homogentisic acid oxidase activity is absent. Its incidence is as low as 0.001%. Ochronosis is the pigmentation of connective tissues and this pigmentation leads to degenerative changes in alkaptonuric patients. Alkaptonuria most prominently involves the lumbar region, but lumbar disc herniation as the presenting feature of alkaptonuria is not common. Only a few patients required surgical intervention. Herewith we report an alkaptonuric patient, who was operated on for lumbar disc herniation. His discectomy material was black and the metabolic disorder was diagnosed retrospectively. This metabolic disease is often recognized on physical re-examination after the black disc material was seen during the operation. Therefore urinalysis for homogentisic acid should be performed in all patients with degenerative changes of the vertebral column. The results of disc surgery in this patient group is successful.

Ochronotic spondyloarthropathy: spinal involvement resembling ankylosing spondylitis.

Ochronotic spondyloarthropathy is a rare metabolic disease with the musculoskeletal manifestations of alkaptonuria. Ochronotic arthropathy patients may have spinal abnormalities similar to ankylosing spondylitis (AS). The proof of sacroiliac involvement or bamboo spine appearance is not sufficient either for diagnosis of ankylosing spondilitis or exclusion of ochronosis. In this report, the case of a 54-year-old woman having ochronosis, with clinically more recognizable axial arthropathy resembling AS, is presented, and the history, clinical presentation, diagnostic techniques, and distinctive diagnosis are reviewed.

Alkaptonuric ochronosis: a case report.

Alkaptonuric ochronosis is a rare autosomal recessive metabolic disorder resulting in a deficiency of homogentisic acid oxidase (alkaptonuria). Ultimately, this enzyme deficiency enables homogentisic acid to accumulate, become polymerized, and be systemically deposited within various tissues of the body (ochronosis). As the disease progresses, tissue deposition of polymerized homogentisic acid eventually will lead to the progressive degeneration of all affected body systems. There is no definitive cure for alkaptonuric ochronosis, and treatment is aimed at controlling and ameliorating symptoms. Multiple systemic complications occur as a result of alkaptonuric ochronosis. In the skeletal system, cervical, thoracic and lumbosacral degenerative disk disease develops, as do widespread arthritic changes in peripheral and weight-bearing joints. In the respiratory system, dyspnea can develop owing to limited chest excursion as a result of stiffening of cartilage in the chest wall. In the cardiovascular system, coronary and valvular calcification frequently occurs. In the genitourinary system, calculi formation and urine discoloration are chief manifestations. This case report describes a 63-year-old man with alkaptonuric ochronosis who sustained a stress fracture of the left femoral neck, necessitating surgical repair, which was done without complications. An overview of alkaptonuric ochronosis is presented, and anesthetic implications are discussed.

New developments in ochronosis: review of the literature.

Ochronosis commonly affects all connective tissue. Recognition of changes secondary to the deposition of ochronotic pigments has increased with advances in diagnostic technology, allowing both improved imaging and early biochemical and genetics-based diagnosis of alkaptonuria, the cause of ochronosis. Successful symptomatic treatment of ochronotic arthropathy with joint replacement has been documented, and a new pharmacotherapeutic agent, nitisinone, is currently under investigation for both prevention and treatment of ochronosis. This review of the literature highlights recently recognized complications, new diagnostic techniques, and treatment options.

Bone metabolism in ochronotic patients.

We investigated skeletal involvement in five male and two female patients with ochronosis, aged 26-82 years. The main parameters of mineral metabolism, together with biochemical markers of bone resorption (urinary N-telopeptides of type I collagen) and formation (serum bone isoenzyme of alkaline phosphatase and serum osteocalcin) were evaluated. In the same subjects lumbar spine and femoral bone mineral density (BMD) were also measured by dual energy X-ray absorptiometry. All patients but the younger 26-year-old patient had lower than normal bone mass at femoral neck and total hip, showing marked osteopenia in three cases and osteoporosis in the remaining three cases. However, at lumbar spine BMD measurement provided spuriously overestimated results, because of intervertebral disc calcification and osteophyte formation. As far as biochemical markers of bone turnover are concerned, the most relevant finding was the increased N-telopeptides of type I collagen urinary excretion. Our results suggest that ochronosis may be associated with increased bone resorption rate leading to an accelerated bone loss. A role of the homogentisic acid polymer deposit in bone matrix and cells, possibly with osteocyte damage and interference in collagen metabolism, might be hypothesized.

Ochronotic arthropathy: rapid destructive hip osteoarthritis associated with metabolic disease.

Ochronosis is a musculoskeletal manifestation of alkaptonuria, an inherited metabolic disorder associated with various systemic abnormalities related to the deposition of homogentisic acid pigment in connective tissues. This report describes a 58-year-old woman with ochronotic arthropathy who, in addition to the typical clinical features of the disorder, presented with rapidly progressive hip osteoarthritis. The destruction of the joint architecture and the severe functional impairment necessitated a total hip replacement which resulted in a satisfactory outcome.