Familial incontinentia pigmenti (IP) is a genodermatosis that segregates as an X-linked dominant disorder and is usually lethal prenatally in males. In affected females it causes highly variable abnormalities of the skin, hair, nails, teeth, eyes, and central nervous system. The prominent skin signs occur in 4 classic cutaneous stages: perinatal inflammatory vesicles, verrucous patches, a distinctive pattern of hyperpigmentation, and dermal scarring. Cells expressing the mutated X chromosome are eliminated selectively around the time of birth, so females with IP exhibit extremely skewed X-inactivation. Li Y., Proc. Natl. Acad. Sci. U.S.A. 96:1042-1047(1999)Jin D.-Y., J. Biomed. Sci. 6:115-120(1999)Rothwarf D.M., Nature 395:297-300(1998).