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Xeroderma pigmentosum (XP) is an inherited condition characterized by an extreme sensitivity to ultraviolet (UV) rays from sunlight. Thus, the areas of the body that are most affected by the condition are the skin and eyes. XP’s name comes from two of its common characteristics: dry skin (xeroderma) and skin color changes (pigmentosum). There are multiple types of XP, some with different features that are captured by the groupings, but all types include sensitivity to UV light.
The onset of symptoms for individuals with XP group A (XPA) is usually in infancy, but some mutations have been associated with later onset. Typically, XPA is diagnosed in infants who have been sunburned after minimal time in sunlight. Affected children also develop excessive freckling on sun-exposed areas. Damage from the UV rays significantly increases the risk for skin cancer in children with XPA. The average age of onset for non-melanoma skin cancer in children with any type of XP is 9 years and for melanoma is 22 years. The eye is also susceptible to damage from UV light resulting in impaired vision due to clouding of the cornea, inflammation of the cornea, non-cancerous growths on the eye, and/or eye cancer.
Other abnormalities that occur in individuals with XPA, but are unlikely to be related to UV damage, include neurological abnormalities and internal cancers. At least 25 to 30% of individuals with XPA have progressive neurological issues that may include hearing loss, difficulty swallowing and talking, movement problems, seizures, and intellectual disability. The risk for internal cancers is thought to be linked to environmental carcinogens, like cigarette smoke and other, potentially uncontrollable, exposures.
Worldwide, XP has been estimated to affect about 1 in 100,000 individuals. For the Caucasian population in the United States, XP is estimated to affect 1 in 250,000 individuals. In Western Europe, 1 in 1,000,000 new cases are seen annually. Of the XP cases in the United States, ~9% are XPA cases.
Higher frequency of XPA cases has been reported in other areas where marriage between blood relatives (consanguinity) is common, or where a few mutations account for the majority of cases. In Japan, ~55% of cases of XP are attributed to a few mutations in the XPA gene; thus the XPA disorder is estimated to affect approximately 1 in 40,000 Japanese individuals. Additional countries in North Africa, the Middle East, and South Asia may also have a higher frequency of XPA patients.
Management for all types of XP involves strictly avoiding sun and UV light especially to the skin and eyes; skin-covering clothing, sunscreen, sunglasses with UV protection are strongly recommended. Avoidance of carcinogens, like cigarette smoke, is also recommended. Treatment of individuals with XP is typically multidisciplinary. Individuals are regularly seen by dermatologists to remove skin growths, and may be prescribed high doses of a special form of vitamin D to prevent additional growths although there are many side effects. Ophthalmologists are also involved in patient care to regularly examine the eyes for damage. A neurologist and audiologist may aid in monitoring, diagnosis, and management of neurological features. Oncologists will become involved if an internal cancer is diagnosed.
The prognosis for an individual with XPA is generally poor due to early onset of symptoms and severity of features. The life expectancy is shortened for many individuals with XPA due to the dramatically increased risk for skin cancer and risk for neurodegeneration. The average life expectancy of an individual with any type of XP with neurological features is 29 years (37 years if neurological features are not present).
Explanations of an extensive number of genetic diseases written by the U.S. Government's National Institutes of Health.
The XP Society is a not-for-profit charitable organization that offers information, support, advocacy, and protection to the XP family, patient and caregiver while promoting research for a cure.
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