Rare genetic disorder of DNA repair in which ability to repair damage caused by ultraviolet (UV) light is deficient.Encyclopedia Entry for Xeroderma Pigmentosum :Xeroderma pigmentosum. XP is an autosomal recessive inherited disorder. This means you must have 2 copies of an abnormal gene in order for the disease or trait to develop. The disorder is inherited from both your mother and father at the same time. The abnormal gene is rare, so the chances of both parents having the gene are very rare. For this reason, it is unlikely for somebody with the condition to pass it on to the next generation, although it is possible. UV light, such as from sunlight, damages the genetic material (DNA) in skin cells. Normally, the body repairs this damage. But in people with XP, the body does not fix the damage. As a result, the skin gets very thin and patches of varying color (splotchy pigmentation) appear.Symptoms usually appear by the time a child is 2 years old. Skin symptoms include: Sunburn that does not heal after just a little bit of sun exposure Blistering after just a little bit of sun exposure Spider-like blood vessels under the skin Patches of discolored skin that get worse, resembling severe aging Crusting of the skin Scaling of the skin Oozing raw skin surface Discomfort when being in bright light ( photophobia ) Skin cancer at a very young age (including melanoma , basal cell carcinoma , squamous cell carcinoma ) Eye symptoms include: Dry eye Clouding of the cornea Ulcers of the cornea Swelling or inflammation of the eyelids Cancer of eyelids, cornea or sclera Nervous system (neurologic) symptoms, which develop in some children, include: Intellectual disability Delayed growth Loss of hearing Muscle weakness of the legs and arms.The health care provider will perform a physical exam, paying special attention to the skin and eyes. The provider will also ask about a family history of XP. Tests that may be done include: Skin biopsy in which skin cells are studied in the laboratory DNA testing for the problem gene The following tests can help diagnose the condition in a baby before the birth: Amniocentesis Chorionic villous sampling Culture of amniotic cells.People with XP need total protection from sunlight. Even the light coming through windows or from fluorescent bulbs can be dangerous. When out in the sun, protective clothing must be worn. To protect the skin and eyes from the sunlight: Use sunscreen with an SPF 15 or higher. Wear long-sleeve shirts and long pants. Wear sunglasses that block UVA and UVB rays. Teach your child to always wear sunglasses when outdoors. To prevent skin cancer, the provider may prescribe medicines, such as a retinoid cream, to apply to the skin. If skin cancer develops, surgery or other methods will be done to remove the cancer.These resources can help you know more about XP: NIH Genetics Home Reference -- ghr.nlm.nih.gov/condition/xeroderma-pigmentosum Xeroderma Pigmentosum Society -- www.xps.org XP Family Support Group -- www.xpfamilysupport.org.Over one half of people with this condition die of skin cancer early in adulthood.Call for an appointment with the provider if you or your child has symptoms of XP.Experts recommend genetic counseling for people with a family history of XP who wish to have children.Chromosomes and DNA Chromosomes and DNA.Patterson JW. Disorders of epidermal maturation and keratinization.