The enzyme deficient in erythropoietic porphyria is:
**Core Concept**
The question tests the understanding of **porphyrias**, a group of disorders caused by defects in the **heme biosynthetic pathway**. Erythropoietic porphyrias are a subset of porphyrias that affect the production of **heme** in erythrocytes.
**Why the Correct Answer is Right**
The correct answer is related to the specific enzyme deficiency in **erythropoietic porphyria**, which involves the **uroporphyrinogen III synthase** enzyme. This enzyme plays a crucial role in the conversion of **hydroxymethylbilane** to **uroporphyrinogen III**.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not the specific enzyme deficient in erythropoietic porphyria.
**Option B:** Incorrect as it is related to a different step in the heme biosynthetic pathway.
**Option C:** Incorrect because it is associated with a different type of porphyria.
**Option D:** Incorrect as the correct enzyme is not listed.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **erythropoietic porphyrias** often present with **photosensitivity** and can lead to severe **skin blistering** and **scarring**.
**Correct Answer:** D. Uroporphyrinogen III synthase