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.