WBR0469
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::Gastrointestinal |
| Prompt | [[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?]] |
| Answer A | AnswerA::Defect of LDL receptors |
| Answer A Explanation | AnswerAExp::A defect in LDL receptors causes familial hypercholesterolemia (FH). |
| Answer B | AnswerB::Defect of apolipoprotein B |
| Answer B Explanation | 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. |
| Answer C | AnswerC::Defect of microsomal triglyceride transfer protein |
| Answer C Explanation | AnswerCExp::Defect of MTP (or MTTP) causes abetalipoproteinemia |
| Answer D | AnswerD::Defect of lipoprotein lipase |
| Answer D Explanation | AnswerDExp::Defect in lipoprotein lipase (LPL) causes chylomicronemia |
| Answer E | AnswerE::Defect of chylomicron |
| Answer E Explanation | AnswerEExp::A defect in chylomicron is not the primary defect in abetalipoproteinemia; it occurs secondary to MTP defect. |
| Right Answer | RightAnswer::C |
| Explanation | [[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.
Abetalipoproteinemia causes a range of symptoms including GI, ocular, hematological, and neurological symptoms. Educational Objective: Abetalipoproteinemia is caused by a genetic mutation of MTP gene. Reference:
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::No |
| Keyword | WBRKeyword::abetalipoproteinemia, WBRKeyword::malabsorption, WBRKeyword::diarrhea, WBRKeyword::microsomal triglyceride transfer protein, WBRKeyword::microsomal, WBRKeyword::triglyceride, WBRKeyword::transfer, WBRKeyword::protein, WBRKeyword::chylomicron, WBRKeyword::apolipoprotein |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |