What is Xeroderma Pigmentosum Group C?
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 specific to each group, but all types include sensitivity to UV light.
XP is often diagnosed in infants who have been sunburned after minimal time in sunlight. However, not all children with XP group C (XPC) will sunburn, though they may have freckle-like changes in skin areas exposed to the sun. Damage from UV rays, regardless of the amount of sun damage observed, significantly increases the risk for skin cancer in children with XPC. 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 or blindness in one or both eyes 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 a portion of individuals with XPC, but are unlikely to be related to UV damage, include neurological abnormalities and internal cancers. Cognitive and motor issues are less likely with XPC, but hearing loss, intellectual disability, autism, and hypoglycemia which can cause neurologic damage have been reported. Risk for internal cancers, primarily cancers of the brain, may be higher than that in other groups, even if the individual does not have any neurological abnormalities. The increased risk for internal cancers is thought to be linked to environmental carcinogens, like cigarette smoke and other, potentially uncontrollable, exposures.
How common is Xeroderma Pigmentosum Group C?
Worldwide, XP has been estimated to affect about 1 in 100,000 individuals. However, XP has been estimated to affect from as high as 1 in 5000 persons to as low as 1 in 1,400,000 individuals, depending on the population. For the Caucasian population in the United States, XP is estimated to affect 1 in 250,000 individuals. In Western Europe, 1 case of XP is seen per 1,000,000 individuals, annually. Of the XP cases in the United States, approximately 40 to 45% are XP group C cases.
In the Japanese population, XP affects approximately 1 in 22,000 individuals, with ~3.5% being attributed to mutations in the XPC gene. A higher frequency of XP cases has been reported in areas where marriage between blood relatives (consanguinity) is common, or where a few mutations account for the majority of cases (founder mutations). A higher frequency of XP cases has been documented in Italy, Turkey, North Africa, and the Middle East. In the Comorian black population of Mayotte, an island off the coast of Africa, XP is found in 1 in 5000 individuals.
How is Xeroderma Pigmentosum Group C treated?
Management for all types of XP involves strictly avoiding sun and UV light especially to the skin and eyes; skin-covering clothing, sunscreen, and 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 A to prevent additional growths (though 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.
What is the prognosis for a person with Xeroderma Pigmentosum Group C?
The prognosis for an individual without neurological features may be good and associated with a normal lifespan. However, the life expectancy is shortened for many individuals with XPC due to the dramatically increased risk for cancers. The average life expectancy of an individual with any type of XP and no neurological features is approximately 37 years (29 years if neurological features are present).