Incontinentia pigmenti: One of the genetic diseases known as neurocutaneous disorders, which cause characteristic patterns of discolored skin and also involve the brain, eyes, nails, and hair. The disease is caused by the genomic rearrangement of the gene for NEMO, or nuclear factor kappa B essential modulator (IKBKG-IKK gamma). Symptoms include discolored skin that appears within two weeks of birth. Neurological abnormalities can include slow motor development, seizures, mental retardation, visual problems, and muscle weakness. Other key features of IP include dental and nail abnormalities. IP is inherited as an X-linked dominant trait, and most affected male fetuses do not survive. In females with IP and certain other X-linked conditions, the X chromosome with the mutant allele is preferentially inactivated; this phenomenon is termed nonrandom (or skewed) X-chromosome inactivation. Also known as Bloch-Sulzberger syndrome.