Xeroderma Pigmentosum

    Xeroderma Pigmentosum (XP) (OMIM 278700 etc.) is a skin condition that results from a 5bp-deletion in the gene for the XPAC protein of the DNA excision repair system. Individuals homozygous for the mutation are unable to reverse T^T dimerization induced by sunlight. XP is characterized by extremely dry skin (xeroderma) and numerous malignant pinpoint tumors that are induced by brief exposure to sunlight.

    The boy on the left shows two skin cancers on his nose, and an irregular distribution of pigment that resembles a severe sunburn (erythemea). The girl on the right has avoided sunlight since diagnosis with XP, and has worked as a successful model. These two cases are relatively mild: XP parients often have massively disfiguring tumors.