A 12-year-old boy has progressive night blindness, anosmia, ataxia, and ichthyosis. Serum shows elevated phytanic acid with normal very long chain fatty acids. MRI demonstrates cerebellar atrophy. The biochemical defect lies in:
- A Peroxisomal biogenesis causing absent peroxisomes
- B Alpha-oxidation of branched-chain fatty acids due to phytanoyl-CoA hydroxylase deficiency ✓
- C Mitochondrial trifunctional protein deficiency
- D Sterol carrier protein-2 deficiency impairing VLCFA transport
Correct answer: B. Alpha-oxidation of branched-chain fatty acids due to phytanoyl-CoA hydroxylase deficiency
Explanation
Refsum disease results from phytanoyl-CoA hydroxylase deficiency, blocking alpha-oxidation, the only route to degrade phytanic acid, a branched-chain fatty acid that beta-oxidation cannot attack at its 3-methyl group. Normal VLCFAs distinguish it from Zellweger syndrome, where peroxisome biogenesis fails globally. Dietary restriction of phytanol (dairy, ruminant fat) plus plasmapheresis slows progression.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.