Xeroderma pigmentosum.

Xeroderma pigmentosum (XP) is a form of general dermatosis characterised by photo-induced cutaneous-ocular impairment and by skin cancers. In addition to these signs, there may also be neurological involvement. This disease is related to a defect in genes within the nucleotide excision repair system for the first seven genetic groups (A-G), and to an abnormality in transcription groups for the eighth group (xeroderma pigmentosum variant - XPV). Cutaneous carcinomas are the most common types of cancer seen. They may begin in childhood. Multiple melanoma commonly occurs during the course of XP but given the frequency of spontaneous regression, the incidence is underestimated. The clinical appearance is characterised by polymorphous lesions with characteristic dyschromia and in most cases it is sufficient to establish the diagnosis. Investigation of unscheduled DNA synthesis (UDS) and cell survival following ultraviolet (UV) radiation were formerly considered the reference examination for laboratory diagnosis. However, these tests are now being replaced by new molecular biology techniques to screen for the genetic mutations characteristic of the disease. These techniques have proved extremely useful in identifying heterozygous patients and in antenatal diagnosis. Photoprotection is the key preventive measure: patients must avoid all exposure to the sun and to artificial sources of UV radiation. The therapeutic arsenal has recently been enriched by several modern therapeutic methods used to destroy cutaneous tumours such as imiquimod and photodynamic therapy (PDT). These approaches are valuable since they eliminate incipient tumours while sparing healthy skin. Surgery and cryosurgery are the most suitable methods for treating cutaneous tumours in children. Chemotherapy may be considered an alternative for the treatment of keratoacanthomas and squamous cell carcinomas (SCC). Cryosurgery may be combined with other therapeutic approaches to eliminate SCC of the lip. Management of these patients in reference centres, coupled with assistance from associations providing support for patients' families, has resulted in improved quality of therapy while slowing down disease progression.