Xeroderma pigmentosum

Xeroderma pigmentosum, commonly known as XP, is an inherited condition characterized by an extreme sensitivity to ultraviolet radiation (UVR), which is present in sunlight and may also be found in some types of artificial lighting. This condition mostly affects the eyes and areas of skin exposed to the sun. Xeroderma pigmentosum is associated with an increased risk of UVR-induced cancers. People with this condition often experience premature aging. Some affected individuals also have problems involving the nervous system.

The signs of xeroderma pigmentosum usually appear in infancy or early childhood. About half of affected children develop a severe sunburn after spending just a few minutes in the sun. The sunburn causes redness and blistering that can last for weeks. However, some children with xeroderma pigmentosum can tan normally. 

By age 2, almost all children with xeroderma pigmentosum develop freckling of the skin in sun-exposed areas (such as the face, arms, and lips); this type of freckling rarely occurs in young children without the disorder. In affected individuals, exposure to sunlight often causes dry skin (xeroderma) and changes in skin coloring (pigmentation). This combination of features gives the condition its name.

People with xeroderma pigmentosum are 10,000 times more likely to develop non-melanoma skin cancer and up to 2,000 times more likely to  develop melanoma skin cancer compared to individuals without this condition. The types of skin cancer that can develop include basal cell carcinoma, squamous cell carcinoma, and melanoma. Most commonly, the first skin cancer appears in affected individuals before age 10. 

Without protection from the sun and other sources of UVR, most people with xeroderma pigmentosum develop multiple skin cancers during their lifetime. These cancers occur most often on  portions of the body that are exposed to the sun, including the face, the lips, the eyelids, the surface of the eyes, the scalp, and the tip of the tongue. Studies suggest that people with xeroderma pigmentosum may also have an increased risk of some internal cancers, including brain tumors, thyroid cancer, and blood cancers. Additionally, affected individuals who smoke cigarettes have a significantly increased risk of lung cancer.

The eyes of people with xeroderma pigmentosum may be painfully sensitive to UVR (photophobia). If the eyes are not protected from UVR, they may become bloodshot and irritated, and the clear front covering of the eyes (the cornea) may become cloudy. In some people, the eyelashes fall out and the eyelids may be thin and turn abnormally inward or outward. In addition to an increased risk of cancer on the surface of the eye, xeroderma pigmentosum is associated with noncancerous growths on the eye. Many of these eye abnormalities can impair vision.

About 30 percent of people with xeroderma pigmentosum develop progressive neurological abnormalities in addition to problems involving the skin and eyes. These abnormalities can include hearing loss, poor coordination, difficulty walking, movement problems, loss of intellectual function, difficulty swallowing and talking, and seizures. When these neurological problems occur, they tend to worsen with time.

Individuals with xeroderma pigmentosum may experience early menopause.

Researchers have identified at least eight genetic forms of xeroderma pigmentosum: complementation group A (XP-A) through complementation group G (XP-G), plus a variant type (XP-V). The types are distinguished by their genetic cause. All of the types increase the risk of skin cancer, although some are more likely than others to be associated with neurological abnormalities.