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A 10-year-old child develops severe, colicky, flank pain. Urinalysis shows yellow-brown
hexagonal crystals. An abdominal x-ray film demonstrates radiopaque staghorn calculi of both
renal pelvises. The nitroprusside cyanide test on urine is positive. Which of the following is the
most likely diagnosis?
A. Cystinuria
B. Familial iminoglycinuria
C. Fanconi syndrome
D. Hartnup disease
E. Hypophosphatemic rickets
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Cystinurea is an autosomal recessive, defect in proximal tubular reabsorption of cystine
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The correct answer is A.
This is cystinuria, which is an autosomal recessive defect of the renal
tubules in which the amino acid cystine cannot be resorbed. The cystine often precipitates in the
urine, forming radiopaque stones (because of enough coprecipitation with calcium) in the bladder
or renal pelvis. The renal pelvis stones often take the form of staghorn calculi. Isolated crystals
of cystine have a characteristic yellow-brown, hexagonal morphology that can be identified in
urine specimens. A positive nitroprusside cyanide test on urine will confirm the diagnosis.
Alkalinization of the urine significantly increases the solubility of the cystine, and is used with
high fluid intake as the mainstay of therapy. However, eventual development of end-stage renal
failure is common.
Familial iminoglycinuria (choice B) is characterized by impaired renal tubular resorption of
proline, hydroxyproline, and glycine.
Fanconi syndrome (choice C) is characterized by glucosuria, phosphaturia, aminoaciduria, and
bicarbonate wasting.
Hartnup disease (choice D) is characterized by a generalized aminoaciduria and more specific
abnormalities of tryptophan metabolism.
Hypophosphatemic rickets (choice E) is characterized by decreased proximal renal tubular
resorption of phosphate and bony abnormalities
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nice question >>>> deserves reposting
