WBR0981

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry, MainCategory::Genetics
Sub Category	SubCategory::Renal
Prompt	[[Prompt::A 17 year old girl presents to the emergency department for severe left flank pain radiating to her groin. The pain started suddenly one hour ago and is severe in nature. The patient reports that this is not the first time it happens to him. According to the patient, previous laboratory exams constantly revealed hexagonal stones. He was informed that the cause of his recurrent kidney stones is a genetic disease in the amino acid transporters in the kidneys. If the patient had a kid with a woman not carrying the disease, what is the percentage his kid will have the disease?]]
Answer A	AnswerA::0%
Answer A Explanation	[[AnswerAExp::Cystinuria is autosomal recessive; therefore, there is 100% risk that the patient will transmit one allele to his kid. However, since the mother is not a carrier, the kid will only have one mutated allele and consequently will not manifest the disease. Therefore, the patient has 0% risk of having cystinuria.]]
Answer B	AnswerB::25%
Answer B Explanation	[[AnswerBExp::Cystinuria is autosomal recessive; therefore, there is 100% risk that the patient will transmit one allele to his kid. However, since the mother is not a carrier, the kid will only have one mutated allele and consequently will not manifest the disease. Therefore, the patient has 0% risk of having cystinuria.]]
Answer C	AnswerC::50%
Answer C Explanation	[[AnswerCExp::Cystinuria is autosomal recessive; therefore, there is 100% risk that the patient will transmit one allele to his kid. However, since the mother is not a carrier, the kid will only have one mutated allele and consequently will not manifest the disease. Therefore, the patient has 0% risk of having cystinuria.]]
Answer D	AnswerD::75%
Answer D Explanation	[[AnswerDExp::Cystinuria is autosomal recessive; therefore, there is 100% risk that the patient will transmit one allele to his kid. However, since the mother is not a carrier, the kid will only have one mutated allele and consequently will not manifest the disease. Therefore, the patient has 0% risk of having cystinuria.]]
Answer E	AnswerE::100%
Answer E Explanation	[[AnswerEExp::Cystinuria is autosomal recessive; therefore, there is 100% risk that the patient will transmit one allele to his kid. However, since the mother is not a carrier, the kid will only have one mutated allele and consequently will not manifest the disease. Therefore, the patient has 0% risk of having cystinuria.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient presents with recurrent kidney stones. The urinalysis repeatedly reveals hexagonal crystal in all previous episodes, 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. Cystinuria is autosomal recessive; therefore, there is 100% risk that the patient will transmit one allele to his kid. However, since the mother is not a carrier, the kid will only have one mutated allele and consequently will not manifest the disease. Educational objective: Cystinuria is an autosomal recessive disease characterized by abnormal reabsorption of cysteine, ornithine, lysine and ornithine (mnemonic: cola) in the proximal convoluted tubules of the kidneys. Reference: First aid for USMLE step 1, 2013. Page 109. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Cystinuria, WBRKeyword::cystine, WBRKeyword::Cysteine
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::