Following the construction of the pedigree, the parents had a series of questions about retinoblastoma and its effect on LD and their family. All forms of retinoblastoma represent a mutation in the gene RB1. The gene is about 180 kb in length with 27 exons that code for a transcript of only 4.7 kb. RB1 gene has been identified as a tumor suppressor gene . The normal retinoblastoma gene product binds DNA and controls the cell cycle at the transition from the G 1 to S phase .
Retinoblastoma arises when loss of function of both alleles of the gene in a retinoblast occurs.
In hereditary retinoblastoma, a chromosome containing the mutant form of RB1 is transmitted in typical autosomal dominant fashion. All of the cells of the body of a person who has inherited this mutation begin with only one normal copy of the retinoblastoma gene. When normal function in both alleles of a tumor suppressor gene is lost, cell division becomes uncontrolled, leading to tumor growth. Hereditary retinoblastomas are often bilateral or multifocal and exhibit an earlier age of onset than sporadic retinoblastomas. Absence or abnormal forms of the protein may result in deregulation of the cell cycle and subsequent cell proliferation.