A New Disorder in UV-Induced Skin Cancer with Defective DNA Repair Distinct from Xeroderma Pigmentosum or Cockayne Syndrome

Photosensitive human syndromes

Photosensitivity in humans can result from defects in repair of light-induced DNA lesions, from photoactivation of chemicals (including certain medications) with sunlight to produce toxic mediators, and by immune reactions to sunlight exposures. Deficiencies in DNA repair and the processing of damaged DNA during replication and transcription may result in mutations and genomic instability. We will review current understanding of photosensitivity to short wavelength ultraviolet light (UV) due to genetic defects in particular DNA repair pathways; deficiencies in some are characterized by an extremely high incidence of cancer in sun-exposed tissues, while in others no cancers have been reported.

Hereditary photodermatoses

Photodermatoses are defined as the abnormal reactions of the skin to photons, usually those of wavelengths found in sunlight. These reactions can be caused by a wide variety of reasons, including defects in repair oflight-induced DNA lesions, the interaction of certain chemicals or medications with sunlight to produce toxic mediators and photo-induced immune reactions. In this chapter we will describe photodermatoses that are associated with hereditary conditions. These can be subdivided into several groups: dermatoses caused by abnormal metabolic conditions, idiopathic photodermatoses, defects in cancer suppressor genes not directly involved in DNA repair but that predispose to photodistributed tumors and photosensitivity due to abnormalities in DNA repair pathways. Special emphasis will be placed on the relatively recently described UV-sensitive syndrome.