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Marfan's Syndrome
Published in K. Gupta, P. Carmichael, A. Zumla, 100 Short Cases for the MRCP, 2020
K. Gupta, P. Carmichael, A. Zumla
Homocystinuria is an important differential diagnosis. This is an autosomal recessive disorder with clinical features resembling Marfan's syndrome and includes peripheral vascular disease, arterial thrombosis, lens dislocation and osteoporosis with increased tendency to bone fractures and mental retardation. The diagnosis is established by the presence of excessive homocystine in the urine. The presence of mitral valve prolapse alone, in the absence of other clinical features, should not be confused with Marfan's. Tall stature is also a feature of Klinefelter's syndrome (see Case 8). There is no satisfactory treatment of Marfan's syndrome. Patients should ideally be followed every year for ocular and cardiac (including echocardiographic) evaluation.
Cobalamin C, D, F, G diseases; methylmalonic aciduria and variable homocystinuria
Published in William L. Nyhan, Georg F. Hoffmann, Aida I. Al-Aqeel, Bruce A. Barshop, Atlas of Inherited Metabolic Diseases, 2020
William L. Nyhan, Georg F. Hoffmann, Aida I. Al-Aqeel, Bruce A. Barshop
In the presence of defective cofactor synthesis, methylmalonate and homocystine accumulate. The amounts are distinctly less than in methylmalonyl CoA mutase deficiency or cystathionine synthase deficiency (Table 4.2). The diagnosis is usually made by organic analysis of the urine, which detects methylmalonate, the most abundant metabolite. Methylcitrate and 3-hydroxypropionate are also identified in this way. Screening tests for methylmalonate (Chapter 3) are also positive, and the diagnosis may first be suspected in this way. Quantitative assay of the urinary amino acids reveals elevated amounts of homocystine. It is important for this purpose to employ fresh urine.
Diseases of the Nervous System
Published in George Feuer, Felix A. de la Iglesia, Molecular Biochemistry of Human Disease, 2020
George Feuer, Felix A. de la Iglesia
The basic metabolic lesion in homocystinuria is the deficiency of cystathione synthetase normally present in the liver and brain. In some patients, this enzyme has been detected in the optic lens. The lack of this enzyme causes accumulation of homocystine and methionine in the blood and excretion of homocystine in the urine in excessive quantities. Several other metabolic products including S-adenosyl-L-methionine are also present in the urine. Levels of cystathionine are low in the brain and other tissues of homocystinuric patients, whereas homocysteine is present in greater amounts. Some homocysteine is methylated to methionine and some is oxidized to homocystine. Folic acid content of the serum is decreased, probably due to increased demands for its metabolite N-5-methyltetrahydrofolic acid, needed in the methyl transfer reactions between homocysteine and methionine. In homocystinuria, cysteine cannot be synthetized from methionine, this is why supplementation of this amino acid becomes essential in these patients.
Proteomic exploration of cystathionine β-synthase deficiency: implications for the clinic
Published in Expert Review of Proteomics, 2020
Hcy-thiolactone is also exported from cells: 99.9% is found in extracellular media [23] or urine [24] and only 0.1% in cells or tissues [25,26]. Hcy is exported from cells as well [19,27] and reacts with protein sulfhydryls and low-molecular weight thiols to form disulfides such as S-Hcy-protein, homocystine (Hcy-S-S-Hcy), and a Cys-S-S-Hcy disulfide in the blood [28–31] (Table 1).