A patient is found to have absent apolipoprotein B in plasma and steatorrhea from birth. Neurological symptoms (ataxia, peripheral neuropathy) develop in childhood despite normal dietary fat intake. This is abetalipoproteinemia. The primary defect is in which protein?

• A Apo B-100 gene mutation causing absent synthesis
• B LDL receptor deficiency
• C Lipoprotein lipase deficiency
• D Microsomal triglyceride transfer protein (MTP) ✓

Explanation

Abetalipoproteinemia (Bassen-Kornzweig syndrome) is caused by autosomal recessive mutations in microsomal triglyceride transfer protein (MTP), which is required for the assembly and secretion of all apo B-containing lipoproteins (chylomicrons in intestine, VLDL in liver). Without MTP, fat-soluble vitamins (A, D, E, K) cannot be absorbed or transported; vitamin E deficiency causes the neurological features (ataxia, peripheral neuropathy, retinitis pigmentosa). Treatment is high-dose vitamin E supplementation. Familial hypobetalipoproteinemia involves apo B gene mutations but is autosomal dominant with partial deficiency.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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