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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{Rim}} (Reviewed by  {{YD}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=Renal
|SubCategory=Renal
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=Renal
|SubCategory=Renal
|Prompt=A 10 year old girl is brought by her mother to the emergency department for severe right flank pain radiating to her groin. The pain started suddenly a couple of hours ago and quickly became very severe. The mother reports that her daughter vomited once today. Urinalysis reveals few red blood cells in the urine in addition to hexagonal crystals. The level of which of the following is probably elevated in the urine of this girl?
|Prompt=A 10-year-old girl is brought to the emergency department (ED) for severe right flank pain that developed acutely over the past 2 hours. The patient explains that her pain radiates to her groin and is only associated with nausea and one episode of yellowish vomiting. When asked, she denies any association between her pain and food intake, change in bowel movement, or change in position. Physical examination is remarkable for costovertebral angle tenderness on the right side. Urinalysis in the ED is remarkable for numerous red blood cells in addition to the presence of hexagonal crystals. Chronic elevation in the urinary concentration of which compound is associated with the development of this patient's condition?
|Explanation=The patient presents with symptoms of [[kidney stone]]s. The [[urinalysis]] reveals hexagonal crystal consistent with cystine stone which occurs in patients with [[cystinuria]]. Cystinuria is autosomal recessive disease characterized by abnormal transporters in the kidneys for cysteine and other positively charged amino acids such as [[ornithine]], [[lysine]] and [[arginine]] leading to impaired absorption of these amino acids. Patients with cystinuria are predisposed to cystine stones (cystine is formed of two cysteine linked by disulfide bond). The treatment of [[cystine]] stones is good hydration and urine alkalinization.
|Explanation=The patient presents with signs and symptoms of [[kidney stone]]s (nephrolithiasis). The [[urinalysis]] is remarkable for hexagonal crystals, which are consistent with the diagnosis of cystine kidney stones that typically develop among patients with [[cystinuria]]. Cystine is composed of two cysteine molecules linked by a disulfide bond. Cystinuria is an autosomal recessive genetic disease characterized by reduced renal reabsorption of positively charged amino acids. It is caused by the presence of abnormal transporters in the the proximal convoluted tubules for cysteine and other positively charged amino acids, such as [[ornithine]], [[lysine]], and [[arginine]]. Cystinuria results in impaired renal reabsorption and excessive excretion of these amino acids, and patients with cystinuria are predisposed to the development of cystine stones. Management of [[cystine]] stones is adequate hydration and urine alkalinization.
 
'''Educational objective:'''
Cystinuria is an autosomal recessive disease characterized by abnormal reabsorption of '''c'''ysteine, '''o'''rnithine, '''l'''ysine and '''o'''rnithine ('''mnemonic: cola''') in the proximal convoluted tubules of the kidneys.
 
'''Reference:'''
First aid for USMLE step 1, 2013. Page 109.
|AnswerA=Lysine
|AnswerA=Lysine
|AnswerAExp=The symptoms and urinalysis findings of this patient are consistent with cystine [[kidney stone]]s in the context of [[cystinuria]]. [[Lysine]] levels are probably elevated in the urine due to the impaired reabsorption of this amino acid by the mutated [[amino acid]] transporter.
|AnswerAExp=The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. The urinary concentration of [[lysine]] is elevated due to the impaired renal reabsorption and excessive excretion of this amino acid by the mutated [[amino acid]] transporter.
|AnswerB=Phenylalanine
|AnswerB=Phenylalanine
|AnswerBExp=The symptoms and urinalysis findings of this patient are consistent with cystine [[kidney stone]]s in the context of [[cystinuria]]. Phenylalanine reabsorption is not impaired in this condition; therefore, the urine level of phenylalanine is not likely elevated.
|AnswerBExp=The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. Phenylalanine reabsorption is not impaired in cystinuria, and urinary concentration of phenylalanine is not typically elevated.
|AnswerC=Tryptophan
|AnswerC=Tryptophan
|AnswerCExp=The symptoms and urinalysis findings of this patient are consistent with cystine [[kidney stone]]s in the context of [[cystinuria]]. [[Tryptophan]] reabsorption is not impaired in this condition; therefore, the urine level of [[tryptophan]] is not likely elevated. Accumulation of tryptophan occurs in [[hartnup]] disease.
|AnswerCExp=The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. Tryptophan reabsorption is not impaired in cystinuria, and urinary concentration of tryptophan is not typically elevated. Excessive urinary excretion and impaired intestinal absorption of tryptophan is characteristic of [[hartnup disease]].
|AnswerD=Homocysteine
|AnswerD=Homocysteine
|AnswerDExp=The symptoms and urinalysis findings of this patient are consistent with cystine [[kidney stone]]s in the context of [[cystinuria]]. [[Homocysteine]] reabsorption is not impaired in this condition; therefore, the urine level of [[homocysteine]] is not likely elevated. Homocysteine level is elevated in [[homocysteinuria]].
|AnswerDExp=The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. Homocysteine reabsorption is not impaired in cystinuria, and urinary concentration of homocysteine is not typically elevated. Serum and urine homocysteine concentrations are elevated in [[homocysteinuria]].
|AnswerE=Leucine
|AnswerE=Leucine
|AnswerEExp=The symptoms and urinalysis findings of this patient are consistent with cystine [[kidney stone]]s in the context of [[cystinuria]]. [[Leucine]] reabsorption is not impaired in this condition; therefore, the urine level of [[leucine]] is not likely elevated. [[Leucine]] level is elevated in [[maple syrup disease]].
|AnswerEExp=The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. Leucine reabsorption is not impaired in cystinuria, and urinary concentration of leucine is not typically elevated. Serum [[leucine]], isoleucine, and valine (branched amino acids) concentrations are elevated in [[maple syrup urine disease]] (MSUD).
|EducationalObjectives=Cystinuria is an autosomal recessive genetic disease characterized by reduced reabsorption of positively charged amino acids. It is caused by the presence of abnormal transporters in the proximal convoluted tubules for cysteine and other positively charged amino acids such as [[ornithine]], [[lysine]] and [[arginine]].
|References=First Aid 2014 page 111
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=Cystinuria, cysteine
|WBRKeyword=Cystinuria, Cysteine, Cystine stone, Nephrolithiasis, Kidney stone, Transporter, Ornithine, Lysine, Arginine
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 02:16, 28 October 2020

 
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Biochemistry
Sub Category SubCategory::Renal
Prompt [[Prompt::A 10-year-old girl is brought to the emergency department (ED) for severe right flank pain that developed acutely over the past 2 hours. The patient explains that her pain radiates to her groin and is only associated with nausea and one episode of yellowish vomiting. When asked, she denies any association between her pain and food intake, change in bowel movement, or change in position. Physical examination is remarkable for costovertebral angle tenderness on the right side. Urinalysis in the ED is remarkable for numerous red blood cells in addition to the presence of hexagonal crystals. Chronic elevation in the urinary concentration of which compound is associated with the development of this patient's condition?]]
Answer A AnswerA::Lysine
Answer A Explanation [[AnswerAExp::The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. The urinary concentration of lysine is elevated due to the impaired renal reabsorption and excessive excretion of this amino acid by the mutated amino acid transporter.]]
Answer B AnswerB::Phenylalanine
Answer B Explanation [[AnswerBExp::The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. Phenylalanine reabsorption is not impaired in cystinuria, and urinary concentration of phenylalanine is not typically elevated.]]
Answer C AnswerC::Tryptophan
Answer C Explanation [[AnswerCExp::The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. Tryptophan reabsorption is not impaired in cystinuria, and urinary concentration of tryptophan is not typically elevated. Excessive urinary excretion and impaired intestinal absorption of tryptophan is characteristic of hartnup disease.]]
Answer D AnswerD::Homocysteine
Answer D Explanation [[AnswerDExp::The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. Homocysteine reabsorption is not impaired in cystinuria, and urinary concentration of homocysteine is not typically elevated. Serum and urine homocysteine concentrations are elevated in homocysteinuria.]]
Answer E AnswerE::Leucine
Answer E Explanation [[AnswerEExp::The patient's presentation and findings on urinalysis are consistent with cystine stones, which often develop among patients with cystinuria. Leucine reabsorption is not impaired in cystinuria, and urinary concentration of leucine is not typically elevated. Serum leucine, isoleucine, and valine (branched amino acids) concentrations are elevated in maple syrup urine disease (MSUD).]]
Right Answer RightAnswer::A
Explanation [[Explanation::The patient presents with signs and symptoms of kidney stones (nephrolithiasis). The urinalysis is remarkable for hexagonal crystals, which are consistent with the diagnosis of cystine kidney stones that typically develop among patients with cystinuria. Cystine is composed of two cysteine molecules linked by a disulfide bond. Cystinuria is an autosomal recessive genetic disease characterized by reduced renal reabsorption of positively charged amino acids. It is caused by the presence of abnormal transporters in the the proximal convoluted tubules for cysteine and other positively charged amino acids, such as ornithine, lysine, and arginine. Cystinuria results in impaired renal reabsorption and excessive excretion of these amino acids, and patients with cystinuria are predisposed to the development of cystine stones. Management of cystine stones is adequate hydration and urine alkalinization.

Educational Objective: Cystinuria is an autosomal recessive genetic disease characterized by reduced reabsorption of positively charged amino acids. It is caused by the presence of abnormal transporters in the proximal convoluted tubules for cysteine and other positively charged amino acids such as ornithine, lysine and arginine.
References: First Aid 2014 page 111]]

Approved Approved::Yes
Keyword WBRKeyword::Cystinuria, WBRKeyword::Cysteine, WBRKeyword::Cystine stone, WBRKeyword::Nephrolithiasis, WBRKeyword::Kidney stone, WBRKeyword::Transporter, WBRKeyword::Ornithine, WBRKeyword::Lysine, WBRKeyword::Arginine
Linked Question Linked::
Order in Linked Questions LinkedOrder::