**Core Concept:**

Primary hyperparathyroidism is a disorder characterized by an overproduction of parathyroid hormone (PTH) by one or more hyperfunctioning parathyroid glands. PTH regulates calcium and phosphorus homeostasis in the body, acting on bones, kidneys, and intestines to maintain calcium levels within a narrow range.

**Why the Correct Answer is Right:**

In primary hyperparathyroidism, the overproduction of PTH leads to increased calcium levels in the blood (hypercalcemia), as PTH stimulates the release of calcium from bones, increases calcium reabsorption in the kidneys, and enhances calcium absorption in the intestines.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because it does not address the primary issue in primary hyperparathyroidism - the overproduction of PTH.
B. Although elevated calcium levels may be present, this statement does not specifically address the cause of the problem, which is an overactive parathyroid gland(s).
C. This statement highlights an effect of high PTH levels but does not address the underlying cause of primary hyperparathyroidism.
D. This option is incorrect because it does not address the primary issue in primary hyperparathyroidism - the overproduction of PTH.

**Clinical Pearl:**

Primary hyperparathyroidism is typically caused by a benign parathyroid adenoma or hyperplasia, and less commonly by parathyroid carcinoma. The diagnosis may be suspected in patients with unexplained hypercalcemia and can be confirmed with blood tests for PTH and calcium levels, as well as imaging studies like sestamibi scan or ultrasound. Treatment typically involves surgery to remove the affected parathyroid gland(s), leading to remission of symptoms and normalization of serum calcium levels in the majority of cases.

**Correct Answer:**

D. The correct answer highlights the primary issue in primary hyperparathyroidism, which is the overproduction of parathyroid hormone (PTH). This statement addresses the cause of the problem, differentiating it from the other options that either describe effects of elevated PTH levels or do not address the primary issue.