What is XP?
Xeroderma Pigmentosum, known as XP, is a rare genetic disease that affects both males and females. People with XP are extremely sensitive to the damaging effects of ultraviolet radiation. If undiagnosed and untreated, XP can lead to the early onset of skin cancer and blindness.
Xeroderma Pigmentosum, known as XP, is a rare genetic disease that affects both males and females. People with XP are extremely sensitive to the damaging effects of ultraviolet radiation. If undiagnosed and untreated, XP can lead to the early onset of skin cancer and blindness. XP is an autosomal recessive disease caused by mutations in genes that are critical for DNA repair. The body must repair DNA when it is damaged by harmful external agents, such as ultraviolet radiation, X-rays and chemicals, but in XP patients that repair mechanism is turned off.
There is no cure for XP. The DNA damage is cumulative and irreversible. Management is limited to avoiding exposure to UV radiation by staying indoors with sunlight blocked out and using protective clothing, sunscreens and sunglasses. Patients with XP and their families face many challenges in daily living. Constant education and reminders of afflicted people’s need to protect themselves from sunlight is paramount in managing XP.
In addition, approximately 25 percent of people with XP develop progressive neurological disease. This is expressed in the form of developmental disabilities and the loss of previously attained abilities, such as walking and talking.
There are at least eight genes that are critical for this DNA repair process. If a person is born with any of the eight genes not functioning correctly, he or she will develop the symptoms of XP. The genes for XP are: XP-A, XP-B, XP-C, XP-D, XP-E, XP-F, XP-G and variant XP. Mutations in the A, C, D and variant genes make up more than 90 percent of XP cases.
In the United States, XP is estimated to occur in one of every one million people, but the populations of some other countries have a higher prevalence of XP. For example, in Japan, XP occurs in one out of every 22,000 people. Incidence of XP in North Africa (Tunisia, Algeria, Morocco, Libya and Egypt) and the Middle East (Turkey, Israel and Syria) is also high, especially in communities in which inbreeding is not uncommon.
On the Navajo reservation, the prevalence of XP is estimated to be one in every 30,000 people.
Caption: Dorey & Yolanda watching the sunset Credit: Maya Stark
» National Center for Biotechnology Information. "Xeroderma Pigmentosum."
» National Institutes of Health. "Understanding Xeroderma Pigmentosum."
» Online Mendelian Inheritance in Man. "Mitochondrial DNA Depletion Syndrome 6."
» PBS. "The Navajo's Ancient Roots."
» Salway, J.G. Medical Biochemistry at a Glance. Hoboken, N.J.: John Wiley & Sons, 2011.