**Core Concept**
Nephrotic syndrome is a kidney disorder characterized by massive proteinuria (>3.5 g/24 hours), hypoalbuminemia, edema, and hyperlipidemia. It is caused by damage to the glomerular filtration barrier, leading to the loss of large amounts of protein in the urine.

**Why the Correct Answer is Right**
The glomerular filtration barrier is composed of the fenestrated endothelium, the basement membrane, and the podocytes. Damage to any of these components can lead to proteinuria. For example, minimal change disease involves damage to the podocytes, while focal segmental glomerulosclerosis involves scarring of the glomeruli.

**Why Each Wrong Option is Incorrect**
**Option A:** Not enough information is provided to assess the validity of this option.
**Option B:** Focal segmental glomerulosclerosis is a cause of nephrotic syndrome, as it involves scarring of the glomeruli and leads to proteinuria.
**Option C:** Membranous nephropathy is a cause of nephrotic syndrome, as it involves thickening of the glomerular basement membrane and leads to proteinuria.

**Clinical Pearl / High-Yield Fact**
It is essential to differentiate between nephrotic and nephritic syndromes, as they have different underlying causes and require different treatments.

**Correct Answer: A.**