NEET PG Medical – 2018 – Question – 31

Correct Answer – B
Ans. is ‘B’ i.e., Citrulline
Types of cystinuria
* Type-I: It is homozygous with a fully recessive form. The patient excretes a large quantity of cystine, ornithine, lysine, and
arginine. Gene involved is rBAT on chromosome-2.
* Type-II & III: These are heterozygous variants of incompletely recessive forms. They excrete cystine, ornithine, lysine, and arginine more than normal but less than the homozygous state (Type-I). Gene involved is SLC7A9 on chromosome 79.
Cystinuria
* Biochemical Defect: An autosomal recessive disorder that results in the formation of a defective amino acid transporter in the renal tubule and intestinal epithelial cells.
* Pathophysiology: The amino acid transporter is responsible for transporting cystine, ornithine, lysine, and arginine. Defective tubular reabsorption of these amino acids in the kidneys results in increased cystine in the urine, which can precipitate and cause kidney stones.
* Clinical Manifestations: Cystine kidney stones presenting with severe, intermittent flank pain and hematuria.
* Lab findings: Increased urinary excretion of cystine, ornithine, arginine, and lysine on urine amino acid chromatography; hematuria and cystine crystals (hexagonal) on the cooling of acidified urine sediment.
* Imaging: Radiopaque kidney stones on CT scan. The most specific test is the cyanide–nitroprusside test
* Treatment: Low-methionine diet; increased fluid intake; acetazolamide to alkalinize the urine. If this fails then patients are usually started on chelating therapy with penicillamine.