**Core Concept**
Porphyrias are a group of rare genetic disorders that result from defects in the biosynthetic pathway of heme, leading to the accumulation of intermediate compounds, known as porphyrins. These disorders can manifest with acute neurological symptoms, cutaneous photosensitivity, and other systemic features.

**Why the Correct Answer is Right**
The correct answer is related to Erythropoietic Protoporphyria (EPP), a form of porphyria characterized by a deficiency of the enzyme ferrochelatase. This enzyme is responsible for inserting iron into the porphyrin molecule to form heme. In EPP, the accumulation of protoporphyrin IX in erythrocytes and other tissues leads to cutaneous photosensitivity, which is a hallmark of this disease. The fair skin of the child makes them more susceptible to the damaging effects of sunlight, resulting in symptoms such as burning, itching, and blistering upon exposure to UV light.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a particular type of porphyria. While porphyrias can present with cutaneous symptoms, the question requires a more specific diagnosis.
**Option B:** This option is incorrect because it does not accurately describe the primary clinical feature of the disease. The correct answer is related to cutaneous photosensitivity, not gastrointestinal symptoms.
**Option C:** This option is incorrect because it describes a different disease altogether. While it may present with some similar symptoms, it is not the correct answer to the question.

**Clinical Pearl / High-Yield Fact**
A key feature of EPP is the presence of scarring and blistering upon exposure to sunlight, which can lead to chronic skin damage and disfigurement. This is particularly important for clinicians to recognize, as it can help guide diagnosis and treatment.

**Correct Answer:** C.