Photosensitive human syndromes

• High sensitivity to sunlight can be caused by defects in certain DNA repair pathways.
• Some DNA repair defects result in high incidence and early appearance of skin tumors.
• Neurodegeneration and growth abnormalities characterize some DNA repair 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.