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 Ataxia-telangiectasia Q  

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20-year-old man is confined to a whell chair due to ataxia-telangiectasia. He has recently experiencing fatigue and shortness of breath. His internist obtains a chest x-ray film,which shows a large mediastinal mass. He undergoes an extensive non-invasive evaluation prior to having the mass removed. Pathology subsequentlyreports that his is a non-Hodgikin lymphoma. Which of the following is the most likely reason that his patient has developed a lymphoreticular malignancy?

A. Defiency in the excision endonuclease.
B. Downregulation of DNA ligase.
C. Formation of thymine dimers.
D. Inability to repair mismatched DNA base pairs.
E. Inactivation of tumor suppressor genes?

answer and explanation,please.



"Ataxia telangiectasia is a chromosome instability syndrome with cerebellar degeneration, immunodeficiency, and an increased risk of cancers; A-T cells are defective in recognizing double-strand DNA damage to signal for repair

...High sensitivity to ionizing radiations. Cell irradiation does not inhibit S phase (DNA synthesis): this is quite pathognomonic of Ataxia Telangiectasia, and shows that G1 checkpoint is deficient; there is a lack of P53, GADD45 and P21 induction, and a fall in radiation-induced apoptosis; P53 phosphorylation at ser15 is deficient


Ill eliminate; a- excision exonuclease is Xeroderma Pigmentosum

answer-c may be related to X.P. because it has to do with REPAIR of thymine dimers-


ataxia talengectasia is due to inactivation of ATM gene whcih codes a kinase essential for p 53 activity ( a tumor supresso r gene )

there is x ray hypersenstivity and predisposition to lymphome


OK it's E
But what does choice B reffer to?



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