xeroderma pigmentosam

8/18/2019 xeroderma pigmentosam

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eroderma

Pigmentosum( P)

着色性干皮病


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• We owe our lives to light from the sun,which

provides the energy captured duringphotosynthesis ( 光合作用 ).

• But the sun also emits a constant stream ofultraviolet rays that ages and mutates the cellsof our skin.

• The hazardous effects of the sun are mostdramatically illustrated y the rare recessivegenetic disorder , Xeroderma Pigmentosum(XP) .


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!atients with "! possess a dificient repair system thatcannot remove segments of #$% damaged y

ultraviolet(紫外线 ) radiation.


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• %s a result ,person with "!are e&tremely sensitive to

sunlight

• 'ven very limited e&posure tothe direct rays of the sun can

produce large numers of

darkpigmented spots on

e&posed areas of the ody

and a greatly elevated risk of

developing disfiguring and

fatal skin cancers.


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The mechanism aout "!

nucleotide e&cision repair deficiency(核苷酸切除修复缺陷 )

• When suected to

ultraviolet radiation

,adacent(相邻的 )

pyrimidines(嘧啶 ) on a

#$% strand have a

tendency to interact withone another to form a

covalent(共价的 ) dimer

comple&.(e&ample as TT

胸腺嘧啶二具体 )


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• *nce TT isformed,ultraviolet radiated#$% will not e

repaired correctly.

• The replication and

the transcription of#$% will einfluencedseriously.


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• T+ -- + a crucial link etween transcription

and #$% repair

• "!B and "!# are two suunits of T+ -- +


8/11 nucleotide e&cision re air

• -n persons with "! who carryspecific mutations in the "!#gene.

• "!# gene encodes a suunitof the T-- + reuired fortranscription initiation(起始 )

• /o, 0utations in "!# couldlead to defect(缺陷 ) in oth#$% repair and transcription


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+ow to help "! patients1

• /ome help for "! patients may e on the way in the

form of skin creams that contain #$% repair enzymes.

• The enzyme are contained in liposomes(脂体 )

that can apparently penetrate (!" ) the outer layer

of the skin and participate in repair pathways


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• "! is a very rare condition ,ut colon cancer(#

$% ) is relatively common.

• -t is estimated that up to 23 percent of colon

cancer cases can e attriuted to mutations in thegenes that encode the proteins reuired formismatch repair.

• 0utations that cripple the mismatch repair systeminevitaly lead to higher mutation rate in othergenes ecause mistakes made during replication

are not corrected.


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xeroderma pigmentosam

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