ABSTRACT
The different types of XP can be subdivided into eight complementation groups related to their different molecular origins, are reported in Table 6.1, but they share the following symptoms:
• Photosensitivity (severe to extreme) • Freckling on photoexposed areas (Figure 6.1)
• Progressive premature aging with poikilodermatous changes (atrophy, lentigo, and telangiectasias) (Figures 6.2 and 6.3)
• Basal cell carcinomas, squamous cell carcinomas and melanoma (in decreasing order) in photoexposed areas, lips, tongue and, rarely, oral and nasal mucosa (Figure 6.4)
• Disfiguring cancer on the face can cause loss of nasal pyramid, orbital structures or external ears, as occurs with repeated surgery (Figures 6.5 and 6.6)
• Rarely, skin angiosarcomas
Extracutaneous findings
• Photophobia, conjunctival cancer, blepharitis, corneal opacities and blindness
• 25% of XP patients show neurologic involvement of different degrees, with low IQ
• Ataxia, abnormal reflex with paresis and progressive central deafness (XP-A) (see Table 6.1)
• Microcephaly, growth retardation and abnormal sexual development in a minority of patients
Genetics and pathogenesis
• XP is inherited as an autosomal recessive disease. • Clinical and cellular photosensitivity is due to
the inability to repair UV-induced DNA damage. Two different DNA-repair processes are defective in XP: the classic nuclear excision repair, divided into two subpathways called the global genome repair system and transcription-coupled repair; and translation synthesis.
