WBR0321

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A 5-year-old boy is diagnosed with a disorder characterized by the deficiency of enzyme X. The enzyme is an essential component of the pathway shown below. Which of the following is most likely to be a clinical feature of this patient's condition? ]]
Answer A	AnswerA::Delayed separation of umbilical cord
Answer A Explanation	AnswerAExp::Leukocyte adhesion deficiency (type I) is due to a defect in LFA-1 integrin. Patients typically present with recurrent bacterial infections with no pus formation and delayed separation of the umbilical cord.
Answer B	AnswerB::Absence of germinal centers on lymph node biopsy
Answer B Explanation	AnswerBExp::Absence of germinal centers on lymph node biopsy due to absence of B cells is found in SCID.
Answer C	AnswerC::Thrombocytopenic purpura and eczema
Answer C Explanation	AnswerCExp::Thrombocytopenic purpura, eczema, and infections are found in patients with Wiskott-Aldrich syndrome, caused by inability of T-cell reorganization of actin cytoskeleton.
Answer D	AnswerD::Self-mutilation and choreoathetosis
Answer D Explanation	AnswerDExp::Self-mutilation and choreoathetosis are found in patients with Lesch-Nyhan syndrome, caused by a deficiency of HGPRT.
Answer E	AnswerE::Precipitation of monosodium urate crystals in joints on arthrocentesis
Answer E Explanation	AnswerEExp::Gout is caused by precipitation of monosodium urate crystals (MSU) in joints. It is a common complication of hyperuricemia.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The patient has adenosine deaminase deficiency, a common cause of severe combined immunodeficiency (SCID). The disease is an X-linked disorder characterized by B cell and T cell deficiency. Accordingly, patients present with recurrent infections, thymic aplasia, and loss of germinal centers on lymph node biopsy. Educational Objective: Adenosine deaminase deficiency is a common cause of SCID References: ]]
Approved	Approved::No
Keyword	WBRKeyword::lymph, WBRKeyword::node, WBRKeyword::biopsy, WBRKeyword::germinal, WBRKeyword::center, WBRKeyword::centers, WBRKeyword::B cell, WBRKeyword::T cell, WBRKeyword::severe, WBRKeyword::combined, WBRKeyword::immunodeficiency, WBRKeyword::SCID, WBRKeyword::adenosine, WBRKeyword::deaminase
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::