**Core Concept**
Nephrotic syndrome is characterized by massive proteinuria (>3.5 g/1.73m^2/day), hypoalbuminemia, hyperlipidemia, and edema. It results from damage to the glomerular filtration barrier, leading to uncontrolled protein loss in the urine.

**Why the Correct Answer is Right**
The hallmark of nephrotic syndrome is the loss of large amounts of protein in the urine, primarily albumin. This occurs due to the disruption of the glomerular filtration barrier, which consists of the podocytes, glomerular basement membrane, and endothelial cells. The correct answer is associated with a primary kidney disease that leads to this disruption.

**Why Each Wrong Option is Incorrect**
**Option A:** Focal segmental glomerulosclerosis (FSGS) is a common cause of nephrotic syndrome, characterized by scarring of the glomeruli and disruption of the filtration barrier.
**Option B:** Minimal change disease (MCD) is another primary kidney disease that presents with nephrotic syndrome, characterized by normal glomeruli on light microscopy but effacement of podocyte foot processes on electron microscopy.
**Option C:** Membranous nephropathy is a primary kidney disease that often presents with nephrotic syndrome, characterized by immune complex deposition on the glomerular basement membrane.

**Clinical Pearl / High-Yield Fact**
To remember the primary kidney diseases associated with nephrotic syndrome, recall the "4 Ms": Minimal change disease, Membranous nephropathy, Focal segmental glomerulosclerosis, and Membranoproliferative glomerulonephritis.

**Correct Answer:** D.