Read Case Study A \"Retinoblastoma\" on page 580 of your textbook, answer questi

Question

Read Case Study A "Retinoblastoma" on page 580 of your textbook, answer questions 1-5.

Gould, Barbara E., Karin C. VanMeter, and Robert J. Hubert. Gould's Pathophysiology for the Health Professions. St. Louis, MO: Elsevier Saunders, 2014. Print.

A.L. is a healthy toddler with a normal perinatal history. Her parents noticed a white spot in the pupil of one eye and request a referral to a pediatric ophthalmologist. Examination of the eye suggests that A.L. has developed a retinoblastoma, a cancer in her eye. This cancer occurs in approximately 1 in every 1500 live births in the United States. The family is referred for genetic testing and counseling. Retinoblastoma can occur because of a change in chromosome 13 or a mutation in the RB 1 gene, which in its normal state prevents normal mitosis. A.L.’s tumor results from mutation of the RB 1 gene, but neither parent shows this mutation.

1. What is the difference in the cause and inheritance of chromosomal changes compared with the inheritance of a mutation in a specific gene?

2. How did the mutation likely occur in the genes in A.L.’s tumor cells?

3. Testing of A.L.’s blood shows no evidence of the RB 1 mutation; how likely is it that A.L. could transmit the mutated gene to her children?

4. How has the mutation caused growth of the tumor in A.L.’s eye?

5. What is the prognosis if the tumor is limited to the intraocular tissues?

Explanation / Answer

Que 1

It is well known that RB1 is tumor suppresser gene, which prevent an uncontrolled cell division. In most of cases, mutation occur in RB1 gene, resulted in prevention of translation of pRB protein. However, under certain condition, additional genetic alterations can influence the development of retinoblastoma and pRB may affects another function of genes and proteins also. When it affects proteins, results in influence on the cell survival, apoptosis, and differentiation. A deletion in RB1 gene region of chromosome 13 may affects other genes, besides RB1, resulted in intellectual disability, slow growth, and distinctive facial features.

Que 2

Mutation may occur through deletion, alteration in gene RB1, or the translated protein may affect the function of other genes or protein.

Que 3

The gene expression is autosomal dominance with 90% penetrance and under certain conditions mutation may occur in early stage of embryo development. Mostly the children with genetic retinoblastoma may not have affected parents and can still transfer their Mutated RB1 gene to their children.

Que 4

The gene RB1 affects the synthesis of protein pRB which is responsible for controlling cell division, and this is resulted in uncontrolled growth in retina tissues. Additionally, the affected gene may also cause ill functioning of others genes. This is explained on basis of two-hit model, in which both alleles need to be pretentious.

Que 5

Children with positive family history, is examined by fundus at regular interval. Besides, dilated eye examination can also be done.

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