Features of cystinuria are
a) Impaired proximal tubular reabsorption of cystine
b) Autosomal recessive
c) Recurrent renal stone
d) All of the above
Correct Answer - D
Answer- D. All of the above
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
cysteine in the urine, which can precipitate and cause kidney stones.
Clinical Manifestations: Cysteine 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 cysteine 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.