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Xeroderma pigmentosum

Xeroderma Pigmentosum (XP) is a rare genetic condition where affected individuals have extreme sun sensitivity, which results in an increased chance of developing skin cancer. It is caused by mutations in one of several different genes.

Characteristics of Xeroderma pigmentosum
Xeroderma pigmentosum (XP) is a chromosomal breakage syndrome characterized by hypersensitivity to ultraviolet (UV) radiation. Affected individuals are at risk for severe sunburn, premature skin aging, blistering, rash, and pigmentation abnormalities even after a minimal amount of sun exposure. The risk for skin cancer is greatly increased in individuals with XP. Affected individuals may develop multiple skin cancers over their lifetime. Age of onset and severity are variable, although individuals with classic XP typically develop skin cancer before the age of 20. Malignancies and complications of the eye are frequent and can include light sensitivity, irritation, weakening of the skin surrounding the eye, and possibly blindness. In addition to complications involving the skin and eyes, approximately 25-30% of individuals with XP develop neurological abnormalities such as diminished deep tendon reflexes, progressive hearing loss, intellectual disability, small head-size (microcephaly), poor coordination, and movement problems.

Diagnosis/Testing
The diagnosis of XP is typically based on clinical exam findings and can be confirmed by cellular tests that look for abnormalities in DNA repair. The genes associated with XP are involved in nucleotide excision repair, which is the primary mechanism the body has for repairing genetic damage caused by exposure to ultraviolet radiation. About 50% of XP cases are found to have two abnormal copies of either the XPA or XPC genes. Other genes known to be associated with XP include ERCC3, ERCC2, DDB2, ERCC4, ERCC5, ERCC1, and POLH.

Management/Surveillance
Individuals with XP are highly recommended to avoid sun and UV exposure as much as possible. The application of sunscreen and UV protective clothing is strongly encouraged. Regular skin, eye, and neurological examinations are suggested for individuals affected with XP. Additionally, since management involves limiting sun exposure, there is risk for vitamin D deficiency. Thus, dietary supplementation of vitamin D is often necessary.

Mode of inheritance
XP is inherited in an autosomal recessive pattern. This means that an individual has to inherit two mutations in a gene associated with XP (i.e., one from each parent) to be affected with XP. If both parents are carriers of an XP gene mutation, they have a 1 in 4 (25%) chance with each pregnancy of having a child with XP.

Risk to family members
Parents of a child with XP are carriers of XP. If a sibling of a child with XP is unaffected, he/she has a 2 in 3 (66%) chance of being a carrier of XP.

Special considerations
None

Resources
Xeroderma Pigmentosum Society
Genetics Home Reference: Xeroderma Pigmentosum
XP Family Support Group

References
Butt, FM. et al. (2010).Xeroderma pigmentosum: a review and case series. Journal of Craniomaxillofacial Surgery 38: 534-537.
Kraemer KH, DiGiovanna JJ. (Updated 2013 Feb 14). Xeroderma Pigmentosum. In: GeneReviews at GeneTests Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2013. Available at http://www.ncbi.nlm.nih.gov/books/NBK1397/. Accessed [12/13/2013].
Schneider K. Counseling About Cancer. Third Edition. Xeroderma Pigmentosum. Chapter 4: Hereditary Cancer Syndromes. Wiley-Blakwell. 2012. Print.

Created:12/2013

Updated:mm/yyyy

Created by:Shannon Stasi, MS, LCGC, Maureen Flynn, MS, LCGC, MPH

Edited by:Seema Jamal, MSc, LCGC



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