WordNet (r) 3.0 (2006):

xeroderma pigmentosum
    n 1: a rare genetic condition characterized by an eruption of
         exposed skin occurring in childhood and photosensitivity
         with severe sunburn; inherited as a recessive autosomal
         trait in which DNA repair processes are defective so they
         are more likely to chromosome breaks and cancers when
         exposed to ultraviolet light