**Core Concept**
The question is testing the student's knowledge of the pathognomonic changes seen in diabetic nephropathy. Diabetic nephropathy is a common complication of diabetes mellitus characterized by damage to the glomeruli, leading to proteinuria and eventually renal failure. Electron microscopy is a valuable tool in diagnosing this condition.

**Why the Correct Answer is Right**
The loss of foot processes is a hallmark feature of diabetic nephropathy. On electron microscopy, the glomerular basement membrane appears thickened, and the podocytes' foot processes are short and fused, leading to a characteristic "effaced" appearance. This change is due to the accumulation of extracellular matrix proteins and the activation of various signaling pathways, including the TGF-β pathway, which contributes to the progression of diabetic nephropathy.

**Why Each Wrong Option is Incorrect**
* **Option A:** Focal segmental glomerulosclerosis (FSGS) is another cause of proteinuria, but it is characterized by segmental sclerosis of the glomeruli rather than loss of foot processes.
* **Option B:** Minimal change disease is a common cause of nephrotic syndrome, but it is characterized by normal electron microscopy findings, with the exception of occasional podocyte foot process effacement.
* **Option C:** Membranous nephropathy is characterized by thickening of the glomerular basement membrane due to immune complex deposition, but it does not typically show loss of foot processes.

**Clinical Pearl / High-Yield Fact**
The loss of foot processes is a sensitive and specific marker for diabetic nephropathy, but it can also be seen in other conditions, such as HIV-associated nephropathy and FSGS.

**Correct Answer: C. Minimal change disease is characterized by normal electron microscopy findings, with the exception of occasional podocyte foot process effacement.**