A 30-year-old man presents with retinitis pigmentosa, peripheral neuropathy, and cerebellar ataxia. Plasma phytanic acid levels are significantly elevated. The dietary restriction of phytol is therapeutic because this patient has a defect in the degradation of phytanic acid via which pathway?
- A Beta-oxidation
- B Alpha-oxidation ✓
- C Omega-oxidation
- D Peroxisomal beta-oxidation
Correct answer: B. Alpha-oxidation
Explanation
Adult Refsum disease results from a defect in phytanoyl-CoA hydroxylase, which catalyzes the first step of alpha-oxidation in peroxisomes. Because phytanic acid has a methyl group at the 3-position, it cannot undergo beta-oxidation directly and requires alpha-oxidation to remove the terminal carbon first. Peroxisomal beta-oxidation handles very long chain fatty acids. Omega-oxidation occurs in the endoplasmic reticulum.
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.