Which of the following causes of hypercalcemia is not associated with high bone turnover?
**Core Concept**
Hypercalcemia is a condition characterized by elevated calcium levels in the blood, which can result from various causes. High bone turnover is a hallmark of certain conditions leading to hypercalcemia, where there is an increased rate of bone resorption and formation.
**Why the Correct Answer is Right**
Familial hypocalciuric hypercalcemia (FHH) is a rare genetic disorder caused by mutations in the calcium-sensing receptor (CaSR) gene, leading to impaired renal calcium excretion and subsequent hypercalcemia. Unlike other conditions, FHH is characterized by low bone turnover, as the primary issue lies in the defective calcium sensing, which does not stimulate excessive bone resorption.
**Why Each Wrong Option is Incorrect**
**Option A:** Primary hyperparathyroidism is caused by hyperfunctioning parathyroid glands, leading to excessive parathyroid hormone (PTH) secretion, which increases bone resorption and turnover. Therefore, it is associated with high bone turnover.
**Option B:** Vitamin D intoxication can cause hypercalcemia by stimulating intestinal calcium absorption and bone resorption, both of which are high-turnover processes.
**Option C:** Malignancy-associated hypercalcemia, typically caused by parathyroid hormone-related protein (PTHrP) or PTH, leads to increased bone resorption and high bone turnover.
**Clinical Pearl / High-Yield Fact**
FHH is a key cause of familial hypercalcemia, often presenting with a family history and low urinary calcium excretion. It's essential to distinguish FHH from other causes of hypercalcemia, as the management and prognosis differ significantly.
**Correct Answer: C. Malignancy-associated hypercalcemia**