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  #1  
Old 02-23-2011
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DNA Retinoblastoma Genetics Question

A newborn male is diagnosed with unilateral retinoblastoma. Molecular analysis of enucleated tumor cells reveals loss of both normal alleles of Rb gene. In comparison, skin fibroblasts of the patient do not show any abnormality at the Rb locus. Which of the following statements regarding his clinical appearance is most accurate?
(A) A predisposition to develop this tumor was inherited by this patient.
(B) His sibs have an increase risk for developing retinoblastoma.
(C) He has increase risk for developing Osteosarcomas in later life.
(D) Both copies of the Rb gene were lost because of mutations in retinoblasts.
(E) He is at a high risk for developing retinoblastoma in the other eye.
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Old 02-23-2011
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hmmm....nice question....thanks
i think the answer is d...the mutation is not inherited because his somatic cells are normal and thus no likelihood of increased risks in siblings and osteosarcoma.....
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Old 02-23-2011
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(C) He has increase risk for developing Osteosarcomas in later life. - This is because Rb gene mutation raises the chances of having Retinoblastoma and Osteosarcomas.
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Old 02-23-2011
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Default E. high risk of retinoblastoma in the other eye

I think it's E - that he will likely have bilateral retinoblastomas. If it had been inherited, then donofitaly would be correct with C, but then B and A could also be true. I agree with pnreddy that the unaffected somatic cells rule out inherited RB mutation. I don't it's D, though, for two reasons. First, don't patients usually inherit one affected RB, and at some point some cells get the "second hit" and develop the potential for malignancy? Also, it seems very probable that E is correct, since it was diagnosed so young. I think that kids with unilateral noninherited retinoblastoma are usually diagnosed as toddlers.

Great question! Looking forward to the answer
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Old 02-23-2011
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Arrow C) He has increase risk for developing Osteosarcomas in later life

My ans is C) He has increase risk for developing Osteosarcomas in later life

Quote:
Originally Posted by donofitaly View Post
(C) He has increase risk for developing Osteosarcomas in later life. - This is because Rb gene mutation raises the chances of having Retinoblastoma and Osteosarcomas.
I agree with you, b/c unilateral retinoblastoma behave in a similar fashion to those bone with bilateral retinoblastoma and predispose to develop osteosarcomas
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Old 02-23-2011
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Default D

The correct ans is (D) Both copies of the Rb gene were lost because of mutations in retinoblasts.
pnreddy is right !!
This is a sporadic form of retinoblastoma because the somatic cells (fibroblasts) of the patient has normal Rb genes. If it was inherited, it would have shown abnormal Rb genes in all cells of the body.
i.e. If he had inherited one copy of mutant(or deleted) Rb gene, all the cells in the body would have only one normal copy of the Rb gene.

For the above reasons, the patients sibs are at no increased riskfor developing retinoblastoma, or he is at no increased risk of developing osteosarcoma, or bilateral retinoblastoma than that of general population.

Well tried guys!
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Old 02-23-2011
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Answer is D.

First, he has not inherited the gene, because fibroblasts at Rb loci are normal. Inherited genes would show in every cell. It is just unfortunate loss of both Rb genes just in, and just in retinal cells.

All other options A, B, C, and E apply to inherited Rb loss.
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Old 02-23-2011
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Great qn buddy, keep posting more!
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