WBR0976

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry, MainCategory::Genetics
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A 28-year-old female is having a genetic counseling for metabolic disorders before her pregnancy. She is very worried that her future baby will carry the “bad gene” that her husband’s family has. Her husband’s brother has died when he was 7 due to coma resulting from an elevated level of ammonia in his blood. After reviewing the records, the lady is informed that her husband’s brother had the most common form of urea cycle disorder. What is the mode of inheritance of this disease?]]
Answer A	AnswerA::Autosomal recessive
Answer A Explanation	AnswerAExp::OTC deficiency is X-linked, whereas other urea metabolism disorders are autosomal recessive.
Answer B	AnswerB::Autosomal dominant
Answer B Explanation	AnswerBExp::OTC deficiency is X-linked, whereas other urea metabolism disorders are autosomal recessive.
Answer C	AnswerC::X-linked recessive
Answer C Explanation	AnswerCExp::OTC deficiency is X-linked, whereas other urea metabolism disorders are autosomal recessive.
Answer D	AnswerD::X-linked dominant
Answer D Explanation	AnswerDExp::OTC deficiency is X-linked, whereas other urea metabolism disorders are autosomal recessive.
Answer E	AnswerE::Y-linked
Answer E Explanation	AnswerEExp::OTC deficiency is X-linked, whereas other urea metabolism disorders are autosomal recessive.
Right Answer	RightAnswer::C
Explanation	[[Explanation::Ornithine transcarmylase (OTC) deficiency is the most common form of urea metabolism disorders. The urea cycle is composed of five enzymes, the deficiency in any of which might lead to a urea metabolism disorder. OTC deficiency is X-linked, whereas other urea metabolism disorders are autosomal recessive. Shown below is a diagram depicting the urea cycle. Educational objective: OTC deficiency is X-linked, whereas other urea metabolism disorders are autosomal recessive. Reference: First aid for USMLE step 1, 2013. Page 107. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::OTC, WBRKeyword::Urea cycle
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::