Bilateral Retinoblastoma Case Study

First, you said only one eye has leukocoria in this infant. Leukocoria is a common clinical feature of retinoblastoma, and this indication is usually a late sign of the disease (Balmer et al., 2006). Retinoblastoma can be either a hereditary disease and a nonhereditary disease. Generally, 60% of the cases of retinoblastoma are nonhereditary, with the remaining 40% being hereditary. Usually, 25% of the hereditary cases have family disease history, which is what we have in this case (NORD). Bilateral retinoblastoma is caused by a “two-hit” mutation on the RB1 gene, which is located on the long arm of chromosome 13, on band 14. The “two” in the two-hit mechanism is referring to the two alleles of the RB1 gene (Knudson, 1971). The first hit in the heritable form of the disease is a heterozygous germline mutation. The other hit is usually a somatic mutation in the other allele (OMIM). Now, that sets the stage for explaining the reasoning behind why only one eye is affected in the patient. The reason is that …show more content…
This hereditary component is inheriting one of the two “hits” on one of the RB1 alleles, which inactivates the gene. The interesting thing is that hereditary retinoblastoma behaves as autosomal dominant, like I said in the first sentence, in pedigrees, but the disease results from a gene in the loss of heterozygosity, through a somatic mutation, on chromosome 13. The chance to pass it on to a child is 45%, since it is a germline disease (Abramson, 2004). Two research studies have found that there the paternal allele retention is preferential in the loss of heterozygosity. They showed that all ten of ten germline mutations were derived from the paternal allele on chromosome 13, with 4 of 7 of the somatic mutations being on the maternal allele. The researchers hypothesized that mutations may be more common during spermatogenesis due to the DNA methylation or environmental exposure (Zhu et al., 1989)(Dryja et al.,