A patient with abetalipoproteinemia (MTP — microsomal triglyceride transfer protein deficiency) presents with fat malabsorption, acanthocytosis, spinocerebellar degeneration, and pigmentary retinopathy. Why do fat-soluble vitamin deficiencies dominate the neurological picture despite normal dietary intake?

• A MTP deficiency impairs bile acid synthesis, reducing fat emulsification and vitamin absorption
• B Acanthocytosis causes accelerated RBC destruction, consuming vitamin E in oxidative stress
• C Absent chylomicron and VLDL assembly means fat-soluble vitamins (A, D, E, K) cannot be packaged or transported in the blood ✓
• D The spinocerebellar degeneration is due to apoB deficiency directly, independent of vitamin malabsorption

Explanation

MTP is required for loading triglycerides and phospholipids onto apoB during chylomicron (in intestine) and VLDL (in liver) assembly. Without MTP, no chylomicrons are formed, so dietary fat and fat-soluble vitamins (A, D, E, K) absorbed into enterocytes cannot be exported into lymph. Vitamin E deficiency is most clinically significant — it causes spinocerebellar ataxia (dorsal column/spinocerebellar tract degeneration) and pigmentary retinopathy. Vitamin A deficiency causes night blindness. Treatment is high-dose oral fat-soluble vitamins.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.