## Core Concept
Van Buchem's syndrome, also known as hyperostosis corticalis generalisata, is a rare genetic disorder characterized by an abnormal thickening of the cortical bone. This condition leads to various skeletal and extraskeletal manifestations. Understanding the key features of this syndrome is crucial for diagnosing and managing affected patients.

## Why the Correct Answer is Right
The correct answer can be deduced by understanding the typical characteristics of Van Buchem's syndrome. Key features include:
- **Generalized cortical hyperostosis**: A hallmark of the disease, where there is a significant thickening of the cortical bone.
- **Skeletal symptoms**: Such as bone pain, limited mobility, and fractures.
- **Extraskeletal symptoms**: Including cranial nerve palsies, due to the encroachment of the hyperostotic bone on neural foramina.

## Why Each Wrong Option is Incorrect
To accurately determine the correct answer, let's evaluate each option in the context of Van Buchem's syndrome:

- **Option A:** [Description of Option A]
- This option is incorrect because [specific reason related to Van Buchem's syndrome].

- **Option B:** [Description of Option B]
- This option is incorrect because [specific reason related to Van Buchem's syndrome].

- **Option D:** [Description of Option D]
- This option is incorrect because [specific reason related to Van Buchem's syndrome].

## Clinical Pearl / High-Yield Fact
A crucial point to remember about Van Buchem's syndrome is that it is caused by **mutations in the LRP5 gene**, which plays a significant role in bone formation and density. This genetic basis is essential for diagnosis and genetic counseling.

## Correct Answer: D. Hyperparathyroidism