Retinoblastoma is an extremely rare childhood form of cancer of the retina of th

Question

Retinoblastoma is an extremely rare childhood form of cancer of the retina of the eye. In some cases, both eyes are affected (bilateral retinoblastoma) and in others only one eye is affected (unilateral retinoblastoma). Bilateral cases occur almost exclusively in hereditary retinoblastoma. An informative difference between bilateral and unilateral retinoblastoma is age of onset as depicted in the figure below. Here a population of children, all of whom ultimately developed retinoblastoma, is represented. The fraction of the population that was tumor free is plotted against age. The curve for unilateral retinoblastoma has a “shoulder” compared to the linear curve for bilateral retinoblastoma.

(1) Which of the following best explains the age of onset data from the graph?

A. In hereditary retinoblastoma, both eyes are

affected so the age of onset is later to allow

more time for the cancer to develop.

B. The genome of the eye mutated more

rapidly than other cells so hereditary

retinoblastoma is observed earlier.

C. Individuals with hereditary retinoblastoma

inherit one mutant copy and one normal copy of Rb, which makes it more likely that these individuals will incur a second or third cancer causing mutation earlier than children that do not inherit the mutation.

D. Hereditary retinoblastoma is an inherited mutation in a tumor suppressor, which generally leads to an earlier age of onset than oncogenes.

(2) Which of the following best explains why both eyes are usually affected in retinoblastoma?

A. In hereditary retinoblastoma, the age of onset is later which allows time for the

cancer to develop on both eyes.

B. In patients with hereditary retinoblastoma, the genome of eye is the primary target

so both eyes are more likely to develop cancer

C. In hereditary retinoblastoma, cells of both eyes as well as all other cells of the body

carry the mutation so it is more likely that both eyes will be affected.

D. The eyes are especially sensitive to mutations in tumor suppressors so it is more likely

that both will be affected.

Explanation / Answer

Retinoblastoma (Rb) is a rare form of cancer that rapidly develops from the immature cells of a retina, the light-detecting tissue of the eye. It is the most common malignant cancer of the eye in children, and it is almost exclusively found in young children.

Approximately 60% of retinoblastomas are sporadic Unilateral in one eye, and the remaining are beacause of Heredity with bilateral in both eyes, with the predisposition to develop the tumor being transmitted as an autosomal dominant trait.”

“In Hereditycases [of retinoblastoma], children inherit one defective copy of the RB gene in the germ line (one hit); the other copy is normal. Retinoblastoma develops when the normal RB allele is mutated in retinoblasts as a result of spontaneous somatic mutation (second time). Because only a single somatic mutation is required for loss of RB function in retinoblastoma families, familial retinoblastoma is inherited as an autosomal dominant trait.”

Ans:1) C)

Individuals with hereditary retinoblastoma inherit one mutant copy and one normal copy of Rb, which makes it more likely that these individuals will incur a second or third cancer causing mutation earlier than children that do not inherit the mutation.

Ans:2) C)

In hereditary retinoblastoma, cells of both eyes as well as all other cells of the body carry the mutation so it is more likely that both eyes will be affected.

Related Questions

Navigate

• Browse (All)
• Browse R
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.