Which one of the following stromal dystrophy is inherited as a recessive condition?
**Core Concept:**
Stromal dystrophies are a group of genetic disorders characterized by degeneration of the stromal cells within the cornea. The stroma is the middle layer of the cornea, which provides its strength, transparency, and refractive power. Inheritance patterns for these disorders include autosomal dominant, autosomal recessive, and X-linked recessive.
**Why the Correct Answer is Right:**
The correct answer, **D.** Leber congenital amaurosis (LCA), is inherited as an X-linked recessive condition. In this mode of inheritance, the gene responsible for the disorder is located on the X chromosome, and males must inherit two mutated copies (one from each parent) to develop the disease. In contrast, females only need to inherit one mutated copy to express the disease symptoms.
**Why Each Wrong Option is Incorrect:**
A. **Option A:** Maroteaux-Lamy syndrome is an X-linked recessive disorder affecting the lysosomal enzymes, but it does not involve the cornea.
B. **Option B:** Cornelia de Lange syndrome is an autosomal dominant disorder characterized by growth retardation, facial dysmorphism, and developmental delays. It does not involve the cornea.
C. **Option C:** Oculocutaneous albinism is an autosomal recessive disorder affecting melanin production, but it does not specifically involve the cornea.
**Clinical Pearl:**
It is essential for students to understand the mode of inheritance for various genetic disorders, as this knowledge can guide the suspicion and diagnosis of these conditions in clinical practice. In the case of inherited corneal dystrophies, it is crucial to consider the mode of inheritance (autosomal dominant, autosomal recessive, or X-linked recessive) when assessing a patient with corneal abnormalities.
**Correct Answer:** **D.** Leber congenital amaurosis (LCA) is an X-linked recessive condition affecting the cornea, which is characterized by congenital blindness and ocular anomalies. In this case, females who inherit the mutated X-linked gene will not typically express symptoms, while males will likely be affected.