POSTER NO: 340

Germline RB1 Mutations in SPoradic Retinoblastoma

C.P. Pang, K.W. Choy, C.B. Yu, S.P. Fan, J. Ng, D.S.C. Lam
Dept of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, 3/F Hong Kong Eye Hospital, 147K Argyle St, Kowloon, Hong Kong

Transmission of retinoblastoma at the cellular level requires loss of function of both alleles at the Rb1 locus. Patients with germline Rb1 mutations can transmit retinoblastoma predisposition to their offspring. Therefore, early detection and characterization of Rb1 mutations among retinoblastoma patients are extremely important for appropriate treatment to improve prognosis and clinical outcome. To determine the frequency and nature of Rb1 gene mutations in patients with sporadic retinoblastoma, we analyzed DNA from peripheral blood. Mutation analysis of the coding and promoter regions of Rb1 was performed by PCR-mediated Conformation Sensitive Gel Electrophoresis followed by direct sequencing. In 16 of 42 retinoblastoma patients, we detected 15 Rb1 germline mutations, including 9 novel sequence alterations: E54X, S114X, I126S, g73779insG, D718N, IVS2+1G>C, IVS14+1G>C, IVS21+1G>C, and a complex alteration g78177G>T/g78176insTT leading to 543X. All of them were predicted to affect the Rb1 large pocket domain by truncating the normal gene products. None of these disease-associated mutations were detected among 100 healthy individuals. Our results indicate that 21% of the sporadic retinoblastoma patients carried a germline Rb1 mutation. This data will be useful to distinguish hereditary from nonhereditary retinoblastoma for proper clinical management, especially if it significantly reduces the number of infant relatives required for clinical surveillance.