Homocystinuria

A genetic disease due to an enzyme deficiency. Among other events, there is a buildup of the amino acid homocystine. Progressive mental retardation is common in untreated cases. The finding of vascular disease and premature arteriosclerosis in persons with homocystinuria led to the theory that homocystine may be a factor in heart disease.

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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 while 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 h.: (1) defect in vitamin B12 metabolism [MIM*277400], (2) deficiency of N-methylene-tetrahydrofolate reductase [MIM*236250], (3) selective intestinal malabsorption of vitamin B12 [MIM*261100], (4) vitamin B12 responsive h., cblE type [MIM*236270], (5) methylcobalamin deficiency, cblG type [MIM*250940], (6) vitamin B12 metabolic defect type 2 [MIM*277410], and (7) transcobalamin II deficiency [MIM*275350].

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ho·mo·cys·tin·uria -.sis-tin-'(y)u̇r-ē-ə n a metabolic disorder inherited as a recessive autosomal trait, caused by deficiency of an enzyme important in the metabolism of homocystine with resulting accumulation of homocystine in the body and its excretion in the urine, and characterized typically by mental retardation, dislocation of the crystalline lenses, skeletal abnormalities, and thromboembolic disease

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n.

an inborn error of metabolism, inherited as an autosomal recessive trait, caused by an enzyme deficiency resulting in an excess of homocysteine in the blood and the presence of homocystine in the urine. Clinically affected individuals are mentally retarded, excessively tall with long fingers (due to overgrowth of bones), generally have loose ligaments (which may result in dislocation of the lens), and have a tendency to form blood clots in the veins and arteries, leading to strokes. Treatment is by diet, which may allow for normal development if the disease is recognized early enough, and high-dose vitamin B₆ therapy.

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ho·mo·cys·tin·uria (ho″mo-sis″tin-uґre-ə) excretion of excess homocystine in the urine, a biochemical abnormality with a variety of autosomal recessive genetic as well as nongenetic causes, characterized by developmental delay, failure to thrive, and neurologic abnormalities, with other features such as hematologic abnormalities varying with specific causes. Principal causes include deficiency of activity of cystathionine β-synthase, any of several genetic disorders causing deficiency of activity of methionine synthase, and nutritional vitamin B₁₂ or folate deficiency; certain drugs can also elevate urinary homocystine. In older literature, the term usually denotes the disorder caused by deficiency of cystathionine β-synthase activity.