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Xeroderma Pigmentosum(XP)

Xeroderma Pigmentosum(XP). 着色性干皮病. We owe our lives to light from the sun,which provides the energy captured during photosynthesis ( 光合作用 ). But the sun also emits a constant stream of ultraviolet rays that ages and mutates the cells of our skin.

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Xeroderma Pigmentosum(XP)

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  1. Xeroderma Pigmentosum(XP) 着色性干皮病

  2. We owe our lives to light from the sun,which provides the energy captured during photosynthesis (光合作用). • But the sun also emits a constant stream of ultraviolet rays that ages and mutates the cells of our skin. • The hazardous effects of the sun are most dramatically illustrated by the rare recessive genetic disorder , Xeroderma Pigmentosum(XP) .

  3. Patients with XP possess a dificient repair system that cannot remove segments of DNA damaged by ultraviolet(紫外线) radiation.

  4. As a result ,person with XP are extremely sensitive to sunlight • Even very limited exposure to the direct rays of the sun can produce large numbers of dark-pigmented spots on exposed areas of the body and a greatly elevated risk of developing disfiguring and fatal skin cancers.

  5. The mechanism about XP------nucleotide excision repair deficiency(核苷酸切除修复缺陷) • When subjected to ultraviolet radiation ,adjacent(相邻的) pyrimidines(嘧啶) on a DNA strand have a tendency to interact with one another to form a covalent(共价的) dimer complex.(example as TT---胸腺嘧啶二具体)

  6. Once TT is formed, ultravioletradiated DNA will not be repaired correctly. • The replication and the transcription of DNA will be influenced seriously.

  7. THF IIH--- a crucial link between transcription and DNA repair • XPB and XPD are two subunits of THF II H

  8. In persons with XP who carry specific mutations in the XPD gene. XPD gene encodes a subunit of the TFII H required for transcription initiation(起始) So, Mutations in XPD could lead to defect(缺陷) in both DNA repair and transcription nucleotide excision repair

  9. How to help XP patients? • Some help for XP patients may be on the way in the form ofskin creamsthat contain DNA repair enzymes. • The enzyme are contained in liposomes(脂质体) that can apparently penetrate (穿过) the outer layer of the skin and participate in repair pathways

  10. XP is a very rare condition ,but colon cancer(结肠癌) is relatively common. • It is estimated that up to 15 percent of colon cancer cases can be attributed to mutations in the genes that encode the proteins required for mismatch repair. • Mutations that cripple the mismatch repair system inevitably lead to higher mutation rate in other genes because mistakes made during replication are not corrected.

  11. Thank You All !

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