Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0003873 (rheumatoid arthritis)
 53,068 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The rare hereditary metabolic disorder alcaptonuria is characterized by the inability to metabolize homogentisic acid, an intermediary compound in the catabolism of the aromatic amino acids phenylalanine and tyrosine. The essentially complete deficiency of homogentisic acid oxidase causes a striking accumulation of homogentisic acid and a derived melanin-like pigment in the connective tissues; the latter is termed ochronosis. Urinary homogentisic acid is oxidized rapidly and becomes a brown or black pigment if alkali is added. Older alcaptonurics have intensely pigmented (ochronotic) connective tissues, primarily the cartilaginous joint surfaces, ribs, intervertebral disks, ear cartilage, etc. They also have an unusual type of arthritis affecting the large weight-bearing joints, i.e. hips, knees and spine, but not the small joints of the hands and feet, as in rheumatoid arthritis. A mechanistic explanation for ochronotic arthritis has not been worked out, but it is clear that accumulation of homogentisic acid in the connective tissues directly or indirectly leads to the arthritic changes. A detailed analysis of the events leading to alcaptonuric arthritis should be worthwhile since it is a model form of arthritis secondary to a well-defined metabolic disorder that must persist for many years before the arthritic complications appear. Possibly other, more common types of arthritis, develop secondarily to metabolic disturbances that involve chemical mediators less obvious, or less easily detected, than homogentisic acid.
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PMID:Alcaptonuria and ochronotic arthritis. 194 88

Homogentisic acid (HGA) spontaneously starts to undergo oxidation and polymerization soon after the beginning of incubation in human blood or plasma at 37 degrees C, and forms plasma soluble melanins (PSM). Haemolysis accompanies this process in blood. The addition of equimolar quantities of antioxidants delays this oxidation significantly (isoascorbic acid by 2:30-4:00 h; glutathione by 3:20-4:05 h; D-penicillamine by 5:00-5:45 h). HGA is a phenylalanine and tyrosine metabolite, related structurally to the catecholamines and other precursors of melanins. HGA is normally metabolized by the enzyme homogentisic acid oxidase. When this enzyme is genetically missing, part of HGA is excreted in the urine, another part polymerizes darkens many tissues (ochronosis), and produces widespread degenerative changes in cartilage and other connective tissues, joints, blood vessels, heart valves, kidneys and in other tissues. Collectively this disorder is known as alcaptonuria, for which no satisfactory treatment is known. The causes of both alcaptonuric arthritis and rheumatoid arthritis are thought to involve increased oxidative stress. Inflammation of joints and connective tissue damage are involved in both diseases. Oxygen radicals are suspected to cause inflammation and cellular damage. Hydroxyl radicals degrade hyaluronic acid (the viscous synovial fluid of joints). High levels of products of free radical reactions, with fluorescence excitation (ex) and emission (em) maxima in the wavelength ranges of those of PSM (ex 320-400 and em 400-470) were reported in the blood sera and synovial fluids of patients with rheumatoid arthritis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Homogentisic acid and structurally related compounds as intermediates in plasma soluble melanin formation and in tissue toxicities. 800 39

Alkaptonuria, a rare autosomal-recessive disorder caused by mutations in the HGD gene and a deficiency of homogentisate 1,2-dioxygenase, is characterized by accumulation of homogentisic acid (HGA), ochronosis, and destruction of connective tissue resulting in joint disease. Certain medications have been reported to cause cutaneous hyperpigmentation resembling that of alkaptonuria. We present 5 such cases. Eighty-eight patients with a possible diagnosis of alkaptonuria were examined at the National Institutes of Health Clinical Center between June 2000 and March 2004. The diagnosis of alkaptonuria was confirmed or ruled out by measurement of HGA in the urine. Five patients with findings consistent with ochronosis, including pigmentary changes of the ear and mild degenerative disease of the spine and large joints, were diagnosed clinically as having alkaptonuria, but the diagnosis was withdrawn based on normal urine HGA levels. All 5 patients were women who had taken minocycline for dermatologic or rheumatologic disorders for extended periods. Minocycline-induced hyperpigmentation should be considered in the differential diagnosis of ochronosis. This could be of increased significance now that minocycline and other tetracyclines have been proposed as therapeutic options for rheumatoid arthritis, bringing a new population of patients with ochronosis and arthritis to medical attention with the potential, but incorrect, diagnosis of alkaptonuria.
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PMID:Minocycline-induced hyperpigmentation masquerading as alkaptonuria in individuals with joint pain. 1552 43

Alkaptonuria is a rare autosomal recessive disorder due to a lack of the enzyme homogentisate dioxygenase, leading to ochronosis, a process of accumulation of a melanin-like polymer of homogentisic acid in cartilage and other collagenous structures. Patients develop severe osteoarthropathy that resembles osteoarthritis. Although the diagnosis of alkaptonuria is not particularly challenging in view of the blue-black discolouration of visible connective tissue and the presence of homogentisic acid in urine, the natural history of alkaptonuria remains poorly understood. Patients would benefit immensely from an objective assessment of their disease status and from a clearer understanding of the pathophysiology and associated physical changes. Isotope bone scans, which are commonly used to identify the extent of involvement of bones in cancerous processes, have also been increasingly used for characterizing the extent of arthropathy in conditions such as osteoarthritis and rheumatoid arthritis. Semiquantitative scores based on the extent of involvement of joints have been used to describe the involvement of large joints in the context of symptomatic treatment for osteoarthritis. A similar semiquantitative isotope bone scan score depending on the involvement of the number of large joints in patients with alkaptonuria can be formulated and validated in a suitable cohort of patients. Bone densitometry measurement using dual-energy X-ray absorptiometry scanning is an internationally accepted tool to assess the risk and extent of osteoporosis, and is increasingly used to assess the additional fracture risk in patients with arthropathy. We believe that, currently, nuclear medicine techniques can provide useful information, which can be incorporated into disease severity scores for alkaptonuria. Once the biological basis for alkaptonuria is better understood, it is feasible that nuclear medicine techniques of even greater sensitivity and specificity can be developed, thereby taking advantage of the vast advances in the fields of radiochemistry, radiopharmacy, positron emission tomography-computed tomography and positron emission tomography-magnetic resonance imaging scanning.
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PMID:Nuclear medicine techniques in the assessment of alkaptonuria. 2187 98

Exogenous ochronosis is characterized by hyperpigmented skin lesions that arise in association with local suppression of homogentisic acid oxidase enzyme. Although it generally develops in association with topical application of chemical agents, it can occasionally develop in association with antimalarial drugs. Here we present the case of a patient with rheumatoid arthritis who developed hyperpigmentation on the face and neck regions during hydroxychloroquine treatment. Hydroxychloroquine is being widely used in rheumatology practice, and cutaneous hyperpigmentation may develop as an adverse effect. In the present case, we emphasize the potential underlying mechanisms through which it may cause cutaneous hyperpigmentation and determine the clinical and histopathological findings of exogenous ochronosis.
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PMID:A case of exogenous ochronosis associated with hydroxychloroquine. 3007 40