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 27 year old male presents to the emergency department for severe left flank pain radiating to the groin and associated with hematuria. The pain suddenly started one hour ago and is severe and stabbing in nature. The patient reports that this is not the first time such pain crises happens to him. According to the patient, previous laboratory exams constantly revealed hexagonal stones in all the previous episodes. 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 also 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. |
| Approved | Approved::No |
| Keyword | WBRKeyword::Cystinuria, WBRKeyword::cystine, WBRKeyword::Cysteine |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |