Most common cause of nephrotic range proteinuria in an adult is-
**Core Concept**
The underlying principle being tested is the identification of the most common cause of **nephrotic range proteinuria** in adults, which is characterized by heavy proteinuria (exceeding 3.5 grams per day). This condition often results from damage to the **glomeruli**, the filtering units of the kidneys.
**Why the Correct Answer is Right**
The most common cause of nephrotic range proteinuria in adults is **Focal Segmental Glomerulosclerosis (FSGS)**, a disease in which scar tissue develops on the parts of the kidneys that filter waste from the blood. FSGS can be primary (idiopathic) or secondary, resulting from various factors including hypertension, diabetes, and obesity. The **podocytes**, crucial for maintaining the glomerular filtration barrier, are damaged in FSGS, leading to massive proteinuria.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while minimal change disease is a common cause of nephrotic syndrome in children, it is less common in adults.
**Option B:** Incorrect as membranous nephropathy, although a cause of nephrotic syndrome, is not the most common cause in adults.
**Option C:** Incorrect because while diabetes can cause nephrotic range proteinuria due to **diabetic nephropathy**, it is not the most common cause of nephrotic syndrome in adults without specifying diabetic nephropathy.
**Option D:** Incorrect as it is not provided.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **FSGS** is increasingly recognized as a common cause of nephrotic syndrome in adults, and its diagnosis requires a kidney biopsy to identify the characteristic segmental scarring of glomeruli.
**Correct Answer:** D. Focal Segmental Glomerulosclerosis.