**Question:** Combination of retinitis pigmentosa and ichthyosis is seen in –

A. X-linked dominant retinitis pigmentosa
B. Autosomal recessive retinitis pigmentosa
C. Autosomal dominant retinitis pigmentosa
D. Autosomal recessive ichthyosis

**Core Concept:**
Retinitis pigmentosa (RP) is a group of inherited retinal degenerative diseases characterized by the progressive loss of rod photoreceptor cells, leading to night blindness and loss of peripheral vision. Ichthyosis is a group of inherited skin disorders characterized by dry, scaly skin. Combining RP and ichthyosis is rare but has been observed in specific genetic disorders.

**Why the Correct Answer is Right:**
The correct answer is **C. Autosomal dominant retinitis pigmentosa**. This type of RP is associated with mutations in the RPGR gene on chromosome 19q13.2. The combination of RP and ichthyosis is seen in cases where the RP gene mutation is inherited from one parent and the ichthyosis gene mutation is inherited from the other parent. This results in a child with both RP and ichthyosis.

**Why Each Wrong Option is Incorrect:**

A. **X-linked dominant retinitis pigmentosa**: This type is associated with mutations in the RP1 gene on Xq28 and is typically inherited from the mother. Combining RP with ichthyosis is not expected in this case.

B. **Autosomal recessive retinitis pigmentosa**: This type is associated with mutations in various genes and is inherited in a recessive manner. Combining RP with ichthyosis is not expected in this case.

D. **Autosomal recessive ichthyosis**: This type is associated with mutations in various genes and is inherited in a recessive manner. Combining RP with ichthyosis is not expected in this case.

**Clinical Pearl:**
Inheritance of genetic disorders can lead to unexpected combinations of diseases in offspring. It is crucial for healthcare professionals to consider these possibilities when evaluating patients with both ocular and dermatological symptoms. This understanding can aid in proper diagnosis, genetic counseling, and targeted genetic testing for families at risk.