**Core Concept**
Vitamin-D Resistant Rickets, also known as X-linked hypophosphatemia, is a rare genetic disorder characterized by impaired phosphate reabsorption in the kidneys. This condition leads to hypophosphatemia, which in turn causes rickets or osteomalacia due to impaired mineralization of bones.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of vitamin-D resistant rickets. In this condition, the impaired phosphate reabsorption in the kidneys is not due to a lack of vitamin D, but rather due to mutations in the PHEX gene, which encodes a protein involved in phosphate regulation. This results in increased levels of fibroblast growth factor 23 (FGF23), which in turn inhibits phosphate reabsorption in the kidneys.

**Why Each Wrong Option is Incorrect**
* **Option A:** Elevated alkaline phosphatase levels are characteristic of vitamin-D resistant rickets, as the body tries to compensate for the impaired mineralization of bones.
* **Option B:** Hypophosphatemia is a hallmark of vitamin-D resistant rickets, resulting from impaired phosphate reabsorption in the kidneys.
* **Option D:** Rickets or osteomalacia are common manifestations of vitamin-D resistant rickets, due to impaired mineralization of bones.

**Clinical Pearl / High-Yield Fact**
Vitamin-D resistant rickets is an X-linked disorder, meaning it primarily affects males, as they have only one X chromosome. Female carriers of the mutation may exhibit milder symptoms.

**Correct Answer: D. Normal vitamin D levels.**