**Question:** Which of the following is an uncommon symptom of deficiency of vitamin A?

A. Night blindness
B. Increased appetite
C. Excessive sweating
D. Dry skin

**Core Concept:** Vitamin A plays a vital role in maintaining vision, immune system function, and epithelial cell differentiation. It is essential for the formation of rhodopsin, a protein that enables vision in low light conditions, particularly night vision.

**Why the Correct Answer is Right:** Night blindness is an uncommon symptom of vitamin A deficiency because it primarily affects the visual system. When vitamin A levels are insufficient, the formation of rhodopsin is impaired, leading to reduced sensitivity to light, particularly at night.

**Why Each Wrong Option is Incorrect:**

B. Increased appetite: This symptom is not specific to vitamin A deficiency and can be attributed to other factors, making it an unlikely choice.
C. Excessive sweating: This is a non-specific symptom and not unique to vitamin A deficiency.
D. Dry skin: Dry skin is a nonspecific symptom and not exclusive to vitamin A deficiency.

**Clinical Pearl:** A comprehensive understanding of vitamin A function and deficiency symptoms is crucial for accurate diagnosis and treatment of patients presenting with such symptoms.

**Correct Answer:** Night blindness (A) is the correct answer as it is an uncommon symptom of vitamin A deficiency and directly relates to the visual system's function, which is primarily affected by vitamin A deficiency. Understanding the importance of vitamin A in maintaining vision and its relation to the visual process can aid in recognizing patients with potential vitamin A deficiency symptoms.