Which of the following statements about Pseudohypoprathyroidism is true:
**Core Concept**
Pseudohypoparathyroidism (PHP) is a rare genetic disorder characterized by resistance to parathyroid hormone (PTH), leading to **hypocalcemia** and **hyperphosphatemia**. The underlying defect involves the **G protein** signaling pathway. This condition affects the regulation of **calcium** and **phosphate** metabolism.
**Why the Correct Answer is Right**
The correct answer is related to the clinical and biochemical features of PHP, which include resistance to PTH, resulting in elevated PTH levels, **hypocalcemia**, and **hyperphosphatemia**. The condition is often associated with **Albright's hereditary osteodystrophy**, which includes features such as short stature, round face, and brachydactyly.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because PHP is not primarily characterized by an excess of PTH.
**Option B:** This option is incorrect as it does not accurately describe the pathophysiological hallmark of PHP.
**Option C:** This option is incorrect because while PHP involves abnormalities in calcium and phosphate metabolism, the description is not specific or accurate enough.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that PHP involves not just biochemical abnormalities but also physical characteristics such as **brachydactyly** and **obesity**, which are part of **Albright's hereditary osteodystrophy**.
**Correct Answer:** D. Resistance to parathyroid hormone.