20.20 : The Retinoblastoma Gene

Tumor suppressor genes are normal genes that can slow down cell division, repair DNA mistakes, or program the cells for apoptosis in case of irreparable damage. Hence, they play an essential role in preventing the proliferation of damaged cells.

The first-ever tumor suppressor gene called Rb was identified in retinoblastoma - a rare eye tumor in children. In inherited forms of the disease, a child inherits one defective copy of the Rb gene, which predisposes them to retinoblastoma. However, when a somatic cell loses the second copy of the gene as well, it triggers the development of tumors. Such individuals develop multiple tumors in both eyes. In the disease's nonhereditary form, a cell undergoes two independent somatic mutations and loses both functional copies of the Rb gene. Such cells become cancerous and lead to the development of a tumor in only one eye.

Retinoblastoma is one of the most common intraocular malignant tumors in children, with an incidence rate of 1 in 15,000 to 1 in 18,000. While the hereditary form comprises 25-35% of the total retinoblastoma cases, the nonhereditary or sporadic form comprises 65-75% of the cases.