Histology of Alport syndrome -a) Foamy cells in interstitiumb) Foamy cells in tubular epithelial cellsc) Thickening of GBM > 100 nmd) Thinning of GBM < 100 nme) Intimal proliferation

**Core Concept**
Alport syndrome is a genetic disorder characterized by glomerulonephritis, hearing loss, and eye abnormalities. It is caused by mutations in the genes coding for type IV collagen, a component of the glomerular basement membrane (GBM).

**Why the Correct Answer is Right**
The correct answer is related to the histopathological findings in Alport syndrome. The GBM is the thin layer of tissue between the glomerular capillaries and the glomerular tuft. In Alport syndrome, the GBM is thinned, which disrupts the normal filtration barrier and leads to glomerulonephritis. The thinning of the GBM is a hallmark of Alport syndrome and is often used as a diagnostic criterion.

**Why Each Wrong Option is Incorrect**
* **Option A:** Foamy cells in the interstitium are characteristic of focal segmental glomerulosclerosis (FSGS), not Alport syndrome.
* **Option B:** Foamy cells in tubular epithelial cells are not a specific feature of Alport syndrome.
* **Option C:** Thickening of the GBM is not a feature of Alport syndrome; instead, the GBM is thinned.
* **Option E:** Intimal proliferation is a feature of other vascular disorders, such as atherosclerosis or vasculitis, and is not a characteristic finding in Alport syndrome.

**Clinical Pearl / High-Yield Fact**
Alport syndrome is an X-linked genetic disorder, and males are more frequently affected than females. The disease is caused by mutations in the COL4A5 gene, which codes for the alpha-5 chain of type IV collagen.

**Correct Answer: D. Thinning of GBM < 100 nm**