A 35-year-old man with abetalipoproteinemia (Bassen-Kornzweig syndrome) presents with steatorrhea, ataxia, retinitis pigmentosa, and acanthocytosis. The fundamental metabolic defect in this disorder is mutation in:
- A Microsomal triglyceride transfer protein (MTP), impairing assembly and secretion of apo B-containing lipoproteins ✓
- B Apolipoprotein B gene, preventing synthesis of both apo B-48 and apo B-100
- C Lecithin-cholesterol acyltransferase (LCAT), preventing HDL maturation
- D ATP-binding cassette transporter ABCA1, reducing cholesterol efflux
Correct answer: A. Microsomal triglyceride transfer protein (MTP), impairing assembly and secretion of apo B-containing lipoproteins
Explanation
Abetalipoproteinemia is caused by mutations in microsomal triglyceride transfer protein (MTP), which is required to lipidated nascent apo B-48 in enterocytes (chylomicron assembly) and apo B-100 in hepatocytes (VLDL assembly). Without MTP function, both chylomicrons and VLDL fail to be assembled and secreted, resulting in absent plasma chylomicrons, VLDL, IDL, and LDL. Fat-soluble vitamins (A, D, E, K) and essential fatty acids cannot be absorbed or transported, explaining the neurological and retinal manifestations.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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