Incontinentia Pigmenti (IP)

Incontinentia pigmenti (IP) belongs to a heterogeneous group of ectodermal dysplasias, which cause abnormalities in structures derived from the ectoderm. It is an X-linked dominant inherited disorder that manifests as abnormalities affecting the skin, coat, teeth, eyes, and hooves. Clinical signs occur only in heterozygous mares (X^IP/X), while male foals (X^IP/Y) die during embryonic development in the uterus, resulting in spontaneous abortion.

The first symptoms can be observed shortly after birth, when affected mares gradually develop skin problems. Pruritic inflammatory skin lesions develop. Affected mares have a distinctive striped coat pattern, similar to the brindle pattern. Areas of hairlessness and hyperpigmentation are commonly present on the skin. The mane and tail are usually very sparse.

Incontinentia pigmenti is caused by a mutation in the IKBKG gene (g.126898409C>T). The disorder may occur in Quarter Horses and related breeds.

Possible genotypes:

• X/X – healthy mare, without the genetic mutation in the IKBKG gene; does not transmit the disease to her offspring.
• X/X^IP – affected mare, carrying the genetic mutation in the IKBKG gene; can transmit the mutation to her offspring. The probability of transmitting the genetic mutation is 50%; the probability of producing an affected female foal (X/X^IP) is 25%.

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Reference:
Towers, Rachel E., et al. “A nonsense mutation in the IKBKG gene in mares with incontinentia pigmenti.” PLoS One 8.12 (2013): e81625.