The genetics of retinoblastoma

Retinoblastoma is a malignant tumor of the eye that affects about one in 20,000 young children and occurs as hereditary and non-hereditary (sporadic) forms. It results from successive loss or inactivation of the two alleles of the Rb1 gene, located in 13q14. A chromosomal deletion in 13q14 is revealed by cytogenetic investigation in about 5% of affected patients. Molecular studies have confirmed that inactivation of both alleles of the Rb1 gene, even by point mutation, is required for tumorigenesis, leading to the concept of antioncogenes or tumor suppressor genes. The protein (p110RB) produced by the Rb1 gene is involved in cell cycle regulation. Absence or abnormal forms of the protein may result in deregulation of the cell cycle and subsequent cell proliferation. Association of p110RB with viral oncoproteins may be a step in tumorigenesis. Differences in penetrance and expressivity among families, could be explained by balanced insertional translocation and by defects of the Rb1 gene, which codes for a shortened Rb protein with partial oncosuppressor function. Techniques allowing analysis of Rb1 mutations can be successfully used to predict or exclude the development of retinoblastoma in newborn infants.