All of the following are excreted in Cysteinuria EXCEPT
Correct Answer: Cystine
Description: (A) Cystine[?]CYSTINE DISORDERS:oCystinuria:-Presence of cystine (and often other amino acids) in the urine due to inability of renal tubules to reasbsorb them. Patient often has kidney stones. Urine & stones can be screened for cystine using cyanide-nitroprusside.oCystinosis:-Inborn error of metabolism, where cystine is incompletely metabolized resulting in cystine deposits in tissues. Isosthenuria common.oBoth are 2 distinct disorders:oBoth of these result in sulfur odor,oBoth of these produce cyanide-nitroprusside test positive.-Quantitative test for presence of cystine gives rise a stable red-purple color (positive for presence of cystine).[?]Metabolic disorders of Cysteine:oCystinuria:-It is the most common inborn error of AA transport.-Autosomal Recessive.-Defect: Impaired Reabsorption of Cystine, Ornithine, Arginine, Lysine (COAL).-This is characterized by urinary excretion of these AAs.[?]Pathogenesis of Cystinuria:oAutosomal recessive disorder.oInvolves a defect in the renal transport of cystine by the tubules. Defect results in lack of cystine reabsorption of the kidney.oHomozygous patients usually the only ones to present with problems.oHeterozygotes have a milder form of cystinuria (cystine crystals found in urine during analysis but don't usually form stones).oCystine is relatively insoluble & increased concentrations leads to precipitation & formation of cystine stones in kidney & urinary tract.oCystinuria is usually identified in the laboratory by cyanide nitro- prusside test.oThe treatment includes restricted ingestion of dietary cystine & high intake of fluids.CYSTINURIAoMnemonic:COLA: Cystine, Ornithine, Lysine, and Arginine.oBiochemical Defect: An autosomal recessive disorder that results in the formation of a defective amino acid transporter in the renal tubule and intestinal epithelial cells.oPathophysiology: The amino acid transporter is responsible for transporting cystine, ornithine, lysine, and arginine. Defective tubular re-absorption of these amino acids in the kidneys results in increased cysteine in the urine, which can precipitate and cause kidney stones.oClinical Manifestations: Cysteine kidney stones presenting with severe, intermittent flank pain and hematuria.oLab findings: Increased urinary excretion of cystine, ornithine, arginine, and lysine on urine amino acid chromatography; hematuria and cystine crystals (hexagonal) on cooling of acidified urine sediment.oImaging: Radiopaque kidney stones on CT scan.oTreatment: Low-methionine diet; increased fluid intake; acetazolamide to alkalize the urine.
Category:
Biochemistry
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