Definition of Xeroderma pigmentosa:

Xeroderma pigmentosa is a rare condition passed down through families in which the skin and tissue covering the eye are extremely sensitive to ultraviolet light.

Causes, incidence, and risk factors:

Xeroderma pigmentosa is an autosomal recessive disorder. It means you must have two copies of an abnormal gene in order for the disease or trait to develop.

Ultraviolet light -- such as that found in sunlight -- damages the genetic material (DNA) in skin cells. Normally, the body repairs this damage. But in persons with xeroderma pigmentosa, the body does not fix the damage. As a result, the skin gets very thin and patches of varying color (splotchy pigmentation) appear.

The condition also causes spidery blood vessels in the skin (telangiectasia) and skin cancer. Skin cancer often occurs before the child is 5 years old.