Cells cultured from an infant suffering from hypotonia and seizures show impaired ability to oxidize very long chain fatty acids and phytanic acid. which cell organelle is defective in the infant
**Core Concept**
The question is testing the student's knowledge of a specific metabolic disorder related to the breakdown of very long chain fatty acids (VLCFAs) and phytanic acid. This disorder is associated with the deficiency of a particular enzyme or organelle involved in the beta-oxidation process.
**Why the Correct Answer is Right**
The impaired ability to oxidize VLCFAs and phytanic acid suggests a defect in the peroxisomal beta-oxidation pathway. Peroxisomes are organelles responsible for the breakdown of these fatty acids, using the enzyme phytanoyl-CoA hydroxylase for phytanic acid. The peroxisomal membrane contains a transport system that shuttles VLCFAs into the peroxisome, where they are broken down by beta-oxidation. A defect in this pathway leads to the accumulation of VLCFAs and phytanic acid, causing the symptoms observed in the infant.
**Why Each Wrong Option is Incorrect**
* **Option A:** Mitochondria are involved in the beta-oxidation of medium- and short-chain fatty acids, but not VLCFAs and phytanic acid, which are primarily broken down in peroxisomes.
* **Option B:** The endoplasmic reticulum is not directly involved in the breakdown of VLCFAs and phytanic acid.
* **Option C:** Lysosomes are involved in the breakdown of complex carbohydrates and proteins, but not fatty acids.
**Clinical Pearl / High-Yield Fact**
This disorder is known as Refsum disease, a rare genetic disorder caused by mutations in the PEX genes, which encode proteins involved in the biogenesis and function of peroxisomes.
**Correct Answer:** D. Peroxisome.