## **Core Concept**
Incontinentia pigmenti is a rare genetic disorder that affects the skin, hair, teeth, nails, eyes, and central nervous system. It is characterized by a distinct sequence of skin manifestations that evolve over time. The disorder is inherited in an X-linked dominant pattern.

## **Why the Correct Answer is Right**
The correct answer, X-linked dominant, is right because incontinentia pigmenti is caused by mutations in the IKBKG gene, which is located on the X chromosome. This gene encodes a protein called NEMO, which plays a critical role in the NF-κB signaling pathway. The X-linked dominant pattern of inheritance means that a single copy of the mutated gene is sufficient to cause the disorder, and it predominantly affects females, while males are usually more severely affected and often do not survive.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Autosomal recessive inheritance is incorrect because incontinentia pigmenti does not follow a pattern where two copies of the mutated gene (one from each parent) are needed to cause the disorder.
- **Option B:** Autosomal dominant inheritance is incorrect because, although the disorder seems to affect each generation and can be transmitted by both males and females, its expression and transmission pattern are not typical of autosomal dominant disorders due to its lethality in males.
- **Option D:** X-linked recessive inheritance is incorrect because incontinentia pigmenti predominantly affects females and has a different expression profile than typical X-linked recessive disorders, which usually affect males.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that incontinentia pigmenti is often lethal in males because they have only one X chromosome. Females, having two X chromosomes, are usually affected but can survive due to X-chromosome inactivation patterns. A classic feature is the evolution of skin lesions through four stages: blistering, verrucous, hyperpigmented, and atrophic.

## **Correct Answer:** . X-linked dominant.