**Question:** All are true regarding Bartter syndrome except?

**Core Concept**
Bartter syndrome is a rare genetic disorder characterized by a defect in the function of the ion transport mechanisms in the thick ascending limb (TAL) of the loop of Henle in the kidneys, leading to impaired salt reabsorption and excessive urinary excretion of potassium, sodium, and chloride ions.

**Why the Correct Answer is Right**
Bartter syndrome is caused by mutations in genes encoding for proteins involved in ion transport in the TAL, such as the Na-K-2Cl cotransporter (NKCC2), the calcium-sensing receptor (CaSR), and the chloride channel (CLCNKB). These mutations disrupt the normal functioning of the ion transport mechanisms, resulting in excessive urinary excretion of ions and hypokalemia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Bartter syndrome is characterized by excessive urinary excretion of potassium, sodium, and chloride ions, not by excessive reabsorption.
**Option B:** This option is incorrect because Bartter syndrome is caused by mutations in genes encoding for proteins involved in ion transport in the TAL, not by defects in the collecting duct.
**Option C:** This option is incorrect because Bartter syndrome is characterized by hypokalemia, not hyperkalemia.

**Clinical Pearl / High-Yield Fact**
Bartter syndrome is a rare genetic disorder that can be diagnosed by measuring the urinary excretion of ions and by genetic testing for mutations in the genes encoding for proteins involved in ion transport in the TAL.

**Correct Answer: None of the above. Bartter syndrome is a rare genetic disorder characterized by excessive urinary excretion of potassium, sodium, and chloride ions, and is caused by mutations in genes encoding for proteins involved in ion transport in the TAL.