Abetalipoproteinaemia presents with fat malabsorption, retinitis pigmentosa, ataxia, and acanthocytosis. The defect is in the MTP (microsomal triglyceride transfer protein) gene, preventing assembly of which lipoprotein?
- A Chylomicrons (in enterocytes) and VLDL (in hepatocytes) ✓
- B HDL
- C LDL only
- D Lipoprotein(a)
Explanation
MTP (encoded by MTTP) is an ER-resident lipid transfer protein that loads triglycerides onto nascent apoB-48 in enterocytes (forming chylomicrons) and onto apoB-100 in hepatocytes (forming VLDL). In abetalipoproteinaemia, both chylomicron and VLDL assembly fail; dietary fat cannot be absorbed from enterocytes (fat malabsorption, steatorrhoea), and TG cannot be exported from liver. Fat-soluble vitamin (A, E, K) deficiency causes retinitis pigmentosa, spinocerebellar degeneration, and coagulopathy respectively. Acanthocytes result from abnormal RBC membrane lipid composition. LDL is derived from VLDL metabolism and disappears secondarily; it is not the primary defect. HDL assembly uses ABCA1 and ApoA-I, not MTP.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.