Xeroderma Pigmentosum, or XP, is a genetic disorder that affects the ability of skin cells to repair the damage done by ultraviolet (UV) light. This means that UV light can easily cause burns, cancers, and other skin malignancies. In extreme cases, those suffering from XP have to avoid exposure to even the smallest amount of sunlight, and even be wary of artificial sources of UV light— such as neon tubes and some energy-saving fluorescent lamps. The necessity of complete avoidance of sunlight has led to individuals with the disease being given the nickname in French of Les Enfants de la Lune (Children of the Moon).
Cancers caused by XP usually develop between the ages of two and ten. Without protection from the sun, a patient is 4,000 times more likely to develop skin cancer than other children. Life expectancy of those who live without protection is less than 20 years. The condition is caused by a recessive gene, which means that both parents must have the gene for XP to manifest itself in their children. A couple giving birth to one baby with XP has a 25 percent chance of having another child with the disease. The incidence of XP in newborn babies worldwide is one in every 300,000, while in Tunisia it is one in 10,000, and in some regions of the country up to one in 100. Part of the reason for this is thought to be intermarriage between cousins, which is still traditional practice in some areas. Lack of public awareness of the disease is also a contributing factor.