A 14 year old boy came to opd with hypopigmented skin patches over forehead and white forelock. The most likely diagnosis is:
**Core Concept**
The question is testing the student's knowledge of a rare genetic disorder that affects pigmentation and hair growth. This condition is characterized by the presence of hypopigmented skin patches and premature graying or whitening of hair, particularly in the forelock area.
**Why the Correct Answer is Right**
The condition is caused by mutations in the _TYR_ gene, which encodes the enzyme tyrosinase. Tyrosinase is crucial for the production of melanin, the pigment responsible for skin and hair color. In this disorder, the loss of functional tyrosinase leads to decreased melanin production, resulting in hypopigmented skin patches and white forelock. The condition is inherited in an autosomal recessive pattern, meaning that the affected individual must inherit two copies of the mutated gene (one from each parent) to express the condition.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the clinical presentation described in the question. The condition described in the question is a rare genetic disorder affecting pigmentation and hair growth, not a common skin condition like acne or eczema.
**Option B:** This option is incorrect because it refers to a different condition altogether, which is characterized by red or pink skin lesions, not hypopigmented skin patches. The condition described in the question is a rare genetic disorder affecting pigmentation and hair growth, not a viral infection like herpes.
**Option C:** This option is incorrect because it does not match the genetic basis of the condition described in the question. The condition is caused by mutations in the _TYR_ gene, not a defect in the melanocortin 1 receptor (MC1R) gene.
**Clinical Pearl / High-Yield Fact**
This condition is also known as piebaldism, a rare genetic disorder that affects melanin production and is characterized by the presence of hypopigmented skin patches and white forelock. It is essential to consider this condition in the differential diagnosis of patients presenting with hypopigmented skin patches and premature graying or whitening of hair.
**Correct Answer: C. Piebaldism.**