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A metabolic disorder characterized by sparse blond hair, long limbs, pectus excavatum, dislocation of lens, failure to thrive, mental retardation, psychiatric disturbances, and thromboembolic episodes; some patients have alleviation of symptoms with pyridoxine whereas others are not responsive; associated with increased urinary excretion of homocystine and methionine. Autosomal recessive inheritance, but carriers have an increased risk of occlusive vascular disease; caused by mutation in the cysthathione beta-synthase gene (CBS) on chromosome 21q. In addition, there are seven other causes of homocystinuria: defect in vitamin B12 metabolism [MIM*277400]; deficiency of N-methylene-tetrahydrofolate reductase [MIM*236250]; selective intestinal malabsorption of vitamin B12 [MIM*261100]; vitamin B12 responsive homocystinuria, cblE type [MIM*236270]; methylcobalamin deficiency, cblG type [MIM*250940], vitamin B12 metabolic defect type 2 [MIM*277410]; and transcobalamin II deficiency [MIM*275350].
homocystinuria/ho·mo·cys·tin·uria/ (-sis″tin-u´re-ah) excessive homocystine in the urine, having various causes, some genetic; symptoms include developmental delay, failure to thrive, neurological abnormalities, and others depending on the cause. Sometimes the term refers specifically to the disorder due to lack of the enzyme cystathionine β-synthase.
Any of several genetic disorders of amino acid metabolism that result in elevated levels of homocystine in the urine and are characterized by varied symptoms including dislocation of the crystalline lens of the eye, cardiovascular and skeletal deformities, and intellectual disability.
Etymology: Gk, homos + (cystine); Gk, ouron, urine
a rare biochemical abnormality characterized by the abnormal presence of homocystine, an amino acid, in the blood and urine, which is caused by any of several enzyme deficiencies in the metabolic pathway of methionine to cystine. The disease is inherited as an autosomal-recessive trait. Its clinical signs are similar to those of Marfan's syndrome, including mental retardation, osteoporosis leading to skeletal abnormalities, dislocated lenses, and thromboembolism. Treatment may include a diet low in methionine and supplementation with large doses of vitamin B6. Long-term results of treatment are not available. homocystinuric, adj.
homocystinuriaMetabolic disease An AR condition due to a defect of cystathionine β—synthase , characterized by ↑ (> 300 µmol/L) homocysteine in serum Clinical Overgrowth of long bones, mental retardation, osteoporosis, ectopia lentis, failure to thrive, sparse blond hair, genu valgum, thromboembolism, fatty liver; most die before age 30 of arterial and venous occlusive disease; lesser ↑ of homocysteine is seen in heterozygotes, in those with ↓ folic acid, vitamin B12, in renal failure and after heart transplants Lab ↑ homocysteine in urine Management Pyridoxine or vitamin B6.
homocystinuriaThe abnormal presence of homocystine in the urine. This may be caused by vitamin B12 deficiency, a B12 metabolic defect, drugs or urinary infection but is usually due to an autosomal recessive enzyme-defect disorder. The hereditary form features sparse blond hair, OSTEOPOROSIS with overgrowth of long bones, a hollowed chest, dislocation of the lenses of the eyes and mental retardation.
An autosomal recessive inherited disorder caused by a cystathionine beta synthase deficiency, which leads to an accumulation of the amino acid methionine and homocysteine. The first signs are ocular; a dislocated lens which may cause diplopia or glaucoma, myopia and occasionally retinal detachment. Systemic signs are blond hair, intellectual impairment and some of the features of Marfan's syndrome (e.g. tall, thin build).
Metabolic disorder characterized by sparse blond hair, long limbs, pectus excavatum, dislocation of lens, failure to thrive, mental retardation, psychiatric disturbances, and thromboembolic episodes.
n a genetic disorder of amino acid metabolism in which the amino acid homocystine appears in the blood and urine; may respond to a low-protein diet and the administration of synthetic amino acids.