**Core Concept**
Albinism is a group of rare genetic disorders characterized by the complete or partial absence of melanin production in the skin, hair, and eyes. This results from mutations in genes encoding enzymes involved in melanin synthesis, such as tyrosinase, tyrosinase-related protein 1 (TYRP1), and SLC45A2. The most common form of albinism is oculocutaneous albinism type 1 (OCA1), caused by mutations in the TYR gene.

**Why the Correct Answer is Right**
Albinism is caused by mutations in genes involved in melanin synthesis. The TYR gene encodes the enzyme tyrosinase, which catalyzes the conversion of tyrosine to L-DOPA, the first step in melanin production. Without functional tyrosinase, L-DOPA cannot be produced, and melanin synthesis is blocked. This leads to the characteristic pale skin, hair, and eye color of individuals with albinism.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because albinism is not caused by a lack of melanocyte-stimulating hormone (MSH) receptors. MSH receptors are involved in regulating melanin production, but they are not directly responsible for the genetic defects that cause albinism.
**Option B:** This option is incorrect because albinism is not caused by a deficiency of the enzyme phenylalanine hydroxylase. Phenylalanine hydroxylase is involved in the breakdown of phenylalanine, but it is not directly involved in melanin synthesis.
**Option C:** This option is incorrect because albinism is not caused by a mutation in the SLC24A4 gene. The SLC24A4 gene is involved in the regulation of melanin production, but it is not directly responsible for the genetic defects that cause albinism.
**Option D:** This option is incorrect because albinism is not caused by a lack of vitamin D. Vitamin D is involved in the regulation of calcium and phosphate metabolism, but it is not directly involved in melanin synthesis.

**Clinical Pearl / High-Yield Fact**
Albinism is a rare genetic disorder that affects approximately 1 in 18,000 to 1 in 50,000 individuals worldwide. It is often associated with increased risk of skin cancer due to the lack of melanin, which provides natural protection against UV radiation.

**Correct Answer: C.**