## **Core Concept**
Dent disease is a rare genetic disorder characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis, and progressive kidney failure. It primarily affects the proximal tubules of the kidneys. The condition is caused by mutations in genes that encode for proteins important in the functioning of the proximal tubular cells.

## **Why the Correct Answer is Right**
The correct answer, **C. CLCN5**, is right because Dent disease type 1 is caused by mutations in the **CLCN5** gene, which encodes for a chloride channel (ClC-5). This channel plays a critical role in the endocytosis and reabsorption of low molecular weight proteins and calcium in the proximal tubules. Mutations in **CLCN5** lead to impaired endocytosis and subsequent loss of low molecular weight proteins in the urine, along with hypercalciuria and nephrocalcinosis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while **NPHS1** and **NPHS2** are genes associated with nephrotic syndrome (e.g., congenital nephrotic syndrome of the Finnish type for **NPHS1** and focal segmental glomerulosclerosis for **NPHS2**), they are not directly associated with Dent disease.
- **Option B:** This option is incorrect as it does not correspond to a known gene directly linked to Dent disease.
- **Option D:** This option is incorrect because **OCRL1** is associated with Lowe syndrome (oculocerebrorenal syndrome), a condition that also affects the kidneys but presents with distinct extrarenal manifestations such as cataracts and intellectual disability.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Dent disease should be suspected in patients with a history of kidney stones, significant proteinuria (particularly of low molecular weight proteins), and a family history of kidney disease. Early diagnosis can help in managing the condition and preventing progression to end-stage renal disease.

## **Correct Answer: C. CLCN5**