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Created page with "{{WBRQuestion |QuestionAuthor={{Rim}} |ExamType=USMLE Step 1 |MainCategory=Biochemistry |SubCategory=Gastrointestinal |MainCategory=Biochemistry |SubCategory=Gastrointestinal ..."
 
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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{Rim}} {{Alison}}
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=Gastrointestinal
|SubCategory=Gastrointestinal
|Prompt=A 6 month old boy is brought by his mother to his physician's office for failure to thrive and steatorrhea.  Following appropriate work-up, the diagnosis of abetalipoproteinemia is made.  Which of the following genetic mutations is the primary defect in abetalipoproteinemia?
|Prompt=A 6-month-old male is brought by his mother to the physician's office for failure to thrive and steatorrhea.  Upon appropriate work-up, you diagnose him with abetalipoproteinemia.  Which of the following genetic mutations is the primary defect in abetalipoproteinemia?
|Explanation=Abetalipoproteinemia is an inherited disorder that is characterized by fat accumulation in enterocytes that cause malabsorption of dietary fat and fat-soluble vitamins. Microsomal transfer protein (MTP) is required for the transfer of creating lipoproteins, such as VLDL, LDL and chylomicrons.  Defect of MTP gene - located on the long arm of chrosome 4 - causes abetalipoproteinemia.  
|Explanation=[[Abetalipoproteinemia]], an inherited disorder characterized by fat accumulation in enterocytes, results in malabsorption of dietary fat and fat-soluble vitamins. [[Microsomal transfer protein]]s (MTP) are required for the creation of [[lipoproteins]], such as VLDL, LDL, and [[chylomicrons]].  A defect of the MTP gene, located on the long arm of chromosome 4, results in [[abetalipoproteinemia]].  


Abetalipoproteinemia causes a range of symptoms including GI, ocular, hematological, and neurological symptoms.  
[[Abetalipoproteinemia]] frequently manifests with GI, ocular, hematological, and neurological symptoms.  


Educational Objective:
|EducationalObjectives=
Abetalipoproteinemia is caused by a genetic mutation of MTP gene.
[[Abetalipoproteinemia]] results from a genetic mutation of the MTP gene.
|References= Aggerbeck LP, Bouma ME, Eisenberg C, et al. Absence of microsomal transfer protein in individuals with abetalipoproteinemia. Science. 1992;258(5084):999-1001


Reference:
Aggerbeck LP, Bouma ME, Eisenberg C, et al. Absence of microsomal transfer protein in individuals with abetalipoproteinemia. Science. 1992;258(5084):999-1001
|AnswerA=Defect of LDL receptors
|AnswerA=Defect of LDL receptors
|AnswerAExp=A defect in LDL receptors causes familial hypercholesterolemia (FH).
|AnswerAExp=A defect in LDL receptors frequently results in [[familial hypercholesterolemia]] (FH).
|AnswerB=Defect of apolipoprotein B
|AnswerB=Defect of apolipoprotein B
|AnswerBExp=Although apoB synthesis decreases in abetalipoproteinema, apoB defect is not the direct mutation that occurs.  It is rather a consequence of the MTP defect and decrease of apolipoprotein synthesis.
|AnswerBExp=Although apoB synthesis frequently decreases in individuals with [[abetalipoproteinema]], an apoB defect is not the direct mutation that leads to [[abetalipoproteinema]].
|AnswerC=Defect of microsomal triglyceride transfer protein
|AnswerC=Defect of microsomal triglyceride transfer protein
|AnswerCExp=Defect of MTP (or MTTP) causes abetalipoproteinemia
|AnswerCExp=A defect of the MTP gene (or MTTP) frequently results in [[abetalipoproteinemia]].
|AnswerD=Defect of lipoprotein lipase
|AnswerD=Defect of lipoprotein lipase
|AnswerDExp=Defect in lipoprotein lipase (LPL) causes chylomicronemia
|AnswerDExp=A defect in lipoprotein lipase (LPL) frequently results in [[chylomicronemia]]
|AnswerE=Defect of chylomicron
|AnswerE=Defect of chylomicron
|AnswerEExp=A defect in chylomicron is not the primary defect in abetalipoproteinemia; it occurs secondary to MTP defect.
|AnswerEExp=A defect in [[chylomicron]] is not the primary defect in individuals with [[abetalipoproteinemia]], but often it occurs secondary to an MTP gene defect.
|RightAnswer=C
|RightAnswer=C
|WBRKeyword=abetalipoproteinemia, malabsorption, diarrhea, microsomal triglyceride transfer protein, microsomal, triglyceride, transfer, protein, chylomicron, apolipoprotein,  
|WBRKeyword=abetalipoproteinemia, malabsorption, diarrhea, microsomal triglyceride transfer protein, enzymes, chylomicron, apolipoprotein, genetics, inheritance, mutation
|Approved=No
|Approved=Yes
}}
}}

Revision as of 14:36, 28 July 2014
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Biochemistry
Sub Category SubCategory::Gastrointestinal
Prompt [[Prompt::A 6-month-old male is brought by his mother to the physician's office for failure to thrive and steatorrhea. Upon appropriate work-up, you diagnose him with abetalipoproteinemia. Which of the following genetic mutations is the primary defect in abetalipoproteinemia?]]
Answer A AnswerA::Defect of LDL receptors
Answer A Explanation [[AnswerAExp::A defect in LDL receptors frequently results in familial hypercholesterolemia (FH).]]
Answer B AnswerB::Defect of apolipoprotein B
Answer B Explanation [[AnswerBExp::Although apoB synthesis frequently decreases in individuals with abetalipoproteinema, an apoB defect is not the direct mutation that leads to abetalipoproteinema.]]
Answer C AnswerC::Defect of microsomal triglyceride transfer protein
Answer C Explanation [[AnswerCExp::A defect of the MTP gene (or MTTP) frequently results in abetalipoproteinemia.]]
Answer D AnswerD::Defect of lipoprotein lipase
Answer D Explanation [[AnswerDExp::A defect in lipoprotein lipase (LPL) frequently results in chylomicronemia]]
Answer E AnswerE::Defect of chylomicron
Answer E Explanation [[AnswerEExp::A defect in chylomicron is not the primary defect in individuals with abetalipoproteinemia, but often it occurs secondary to an MTP gene defect.]]
Right Answer RightAnswer::C
Explanation [[Explanation::Abetalipoproteinemia, an inherited disorder characterized by fat accumulation in enterocytes, results in malabsorption of dietary fat and fat-soluble vitamins. Microsomal transfer proteins (MTP) are required for the creation of lipoproteins, such as VLDL, LDL, and chylomicrons. A defect of the MTP gene, located on the long arm of chromosome 4, results in abetalipoproteinemia.

Abetalipoproteinemia frequently manifests with GI, ocular, hematological, and neurological symptoms.
Educational Objective: Abetalipoproteinemia results from a genetic mutation of the MTP gene.
References: Aggerbeck LP, Bouma ME, Eisenberg C, et al. Absence of microsomal transfer protein in individuals with abetalipoproteinemia. Science. 1992;258(5084):999-1001]]

Approved Approved::Yes
Keyword WBRKeyword::abetalipoproteinemia, WBRKeyword::malabsorption, WBRKeyword::diarrhea, WBRKeyword::microsomal triglyceride transfer protein, WBRKeyword::enzymes, WBRKeyword::chylomicron, WBRKeyword::apolipoprotein, WBRKeyword::genetics, WBRKeyword::inheritance, WBRKeyword::mutation
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