**Core Concept**
WAGR syndrome, an acronym for Wilms tumor, Aniridia, Genitourinary anomalies, and mental Retardation, is a rare genetic disorder caused by a deletion of part of chromosome 11p13. This deletion leads to the loss of function of several critical genes, including the PAX6 gene, which plays a key role in eye development.

**Why the Correct Answer is Right**
Aniridia, characterized by the partial or complete absence of the iris, is a hallmark feature of WAGR syndrome. This occurs due to the deletion of the PAX6 gene, which is necessary for the proper development of the iris. The PAX6 gene helps regulate the expression of other genes involved in eye development, including those responsible for the formation of the iris. In the absence of functional PAX6 protein, the iris fails to develop properly, leading to aniridia.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lens coloboma, a hole in the lens, is not a characteristic feature of WAGR syndrome. While lens coloboma can occur in conjunction with aniridia, it is not a defining feature of WAGR syndrome.
* **Option B:** Retinitis pigmentosa, a group of genetic disorders affecting the retina, is not associated with WAGR syndrome. Retinitis pigmentosa typically presents with night blindness, peripheral vision loss, and eventually central vision loss, which is not a characteristic feature of WAGR syndrome.
* **Option D:** Trabeculodysgenesis, a disorder of the trabecular meshwork, is not a feature of WAGR syndrome. Trabeculodysgenesis is associated with glaucoma, but it is not a characteristic feature of WAGR syndrome.

**Clinical Pearl / High-Yield Fact**
WAGR syndrome is a rare genetic disorder that highlights the importance of the PAX6 gene in eye development. Aniridia, a hallmark feature of WAGR syndrome, is a critical diagnostic clue for this condition.

**✓ Correct Answer: C. Aniridia**