Which type of inheritance does Incontinentia pigmenti fall into?

• A. X-linked dominant
• B. X-linked recessive
• C. Autosomal dominant
• D. Autosomal recessive

Answer: (A)

Incontinentia pigmenti is categorized as an X-linked dominant trait because it is generally caused by mutations in the IKBKG gene located on the X chromosome. This means that a single mutated copy of the gene in females (who have two X chromosomes) is sufficient to manifest symptoms of the disorder, while males, who have only one X chromosome, can have more severe manifestations if they inherit the mutation.

In X-linked dominant inheritance, traits are passed from an affected parent to offspring, regardless of gender, but the effects can differ between males and females due to their differing chromosome compositions. Females with one mutated copy of the gene can have varying degrees of symptoms, while males with the mutation often experience more severe effects or may not survive to birth.

The other types of inheritance listed do not apply to Incontinentia pigmenti because the disorder is specifically related to an X-linked dominant mechanism, which is characterized by the aforementioned patterns of inheritance and expression in affected individuals. This distinction is crucial for understanding how genetic conditions like Incontinentia pigmenti are transmitted and expressed in families.