A.L. is a healthy toddler with a normal perinatal history. Her parents notice a

Question

A.L. is a healthy toddler with a normal perinatal history. Her parents notice 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 and approximately 250 children are diagnosed each year 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 RB1 gene, which in its normal state prevents abnormal mitosis. A.L.'s tumor results from mutation of the RB1 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 RB1 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

There are two types of reteinoblastoma mutations are present one is germinal 2)non germinal

In 40% reteinoblastoma mutations are germinal mutations means mutation occurs in all of the body cells(including sperm and ova) .People with germinal mutations have a family history and have autosomal daminant inheritance patern .A person with germinal retinoblstoma may inherited one alterd copy from his parents or the other altered gene may be the result of a new mutationthat occurs in an egg or sperm cell or just after fertilization(two hit hypothesis)

In 60% non germinal form of retinoblastomas have no family history, non-germinal retinoblastoma are not at risk of passing these RB1 mutations to their children.Somatic mutation or other alteration in a retinal cell leads to loss of function of the normal alleles , thus initiating development of a tumor.Non germinal retinoblastoma usually occurs in one place in one eye only.

3) loss of heterozygosity (LOH) is a phenomenon usally observed in retino blastoma patients for this reason blood does not show evidence of the Rb mutations.

In AL case we have to look on family history ,if family history have Rb mutations ,shows germinal form of retinoblastoma and pattern of inheritance is autosomal daminent so more chances are there mutation passes to next generation.If no family history, less likely passes to next generation .

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