The genetics of the photodermatoses.

There are multiple genetic disorders with photosensitivity. The first large group consists of the porphyrias about which a great amount of knowledge has accumulated. The second group is not as well-defined for they are the heredodegenerative disorders of which xeroderma pigmentosum is the most important because here the basic defect in DNA repair is known. Some of the aminoacidurias may cause photosensitivity because of pigment dilution or pellagra-like states. The last group consisting of Darier's, polymorphic light eruption and others are poorly understood, and photosensitivity here is not present in all cases.