Xeroderma Pigmentosum

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What is xeroderma pigmentosum?

Xeroderma pigmentosum (XP) is a hereditary condition characterized by extreme sun sensitivity, leading to a very high risk of skin cancer. Eye problems are also common. Neurologic problems—€”including learning disabilities, progressive hearing loss, progressive neuromuscular degeneration, loss of some reflexes, and occasionally, tumors in the central nervous system—occur in some people with XP.

People with XP are extremely sensitive to ultra-violet (UV) radiation. This includes UVA, UVB, and UVC rays. Exposure to even a very small amount of UV radiation leads to severe sunburn and blistering, beginning at a very young age. People with XP also have increased freckling, as well as areas of lighter (hypo) skin pigmentation. They also have very dry skin. There is a high risk of squamous cell and basal cell skin cancers and melanoma.

People with XP also have eye problems, especially with the eyelids. Like their skin, their eyes are also very sensitive to light, which gives them a slightly increased risk of cancer of the eye. Cancers of the lips, mouth, and the tip of the tongue have also been reported. In addition, people with XP may have neurological complications, including developmental disabilities, mental retardation, and high-frequency hearing loss that leads to deafness.

What causes XP?

XP is a genetic condition. This means that the risk of XP can be passed from generation to generation in a family. Mutations (alterations) in at least eight different genes are known to play a role in XP. Research is ongoing to learn more about XP.

How is XP inherited?

Normally, every cell has two copies of each gene: one inherited from the mother and one inherited from the father. XP follows an autosomal recessive inheritance pattern, in which case a mutation must be present in both copies of the gene in order for a person to be affected. This means that both parents must pass on a gene mutation for a child to be affected. A person who has only one copy of the gene mutation is called a carrier. When both parents are carriers of a recessive mutation in the same gene, there is a 25% chance that a child will inherit two mutations and be affected.

How common is XP?

XP is considered to be very rare. It is estimated that one in one million people in the United States may have XP. XP appears to be somewhat more common in Japan, North Africa, and the Middle East.

How is XP diagnosed?

XP is suspected when a person shows signs of extreme sun sensitivity. Signs of sun sensitivity include severe burning and blistering with only a small amount of sun exposure or even exposure to fluorescent lights. These signs can be present in infancy. Young children may also be suspected of having XP if they have a large number of freckles on their face. The characteristic eye and neurologic problems may also increase the doctor's suspicion that a person has XP. The clinical signs of XP vary widely, depending on the type of mutations involved and the extent of sun exposure that a person with XP has had.

Genetic testing for mutations in the genes associated with XP is available, mainly as part of research studies. Because there are at least eight genes associated with XP, laboratory screening tests are recommended to help determine which of the eight genes is likely to be causing XP in a family.

What are the estimated cancer risks associated with XP?

People with XP have a nearly 100% risk of developing multiple skin cancers if their environment is not carefully controlled. The first diagnosis of skin cancer commonly occurs in childhood. There may be an increased risk of cancer developing in the eyes and around the mouth area.

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