THE SPECTRUM OF RB1 GERM-LINE MUTATIONS IN HEREDITARY RETINOBLASTOMA

We have searched for germ-line RB1 mutations in 119 patients with here ditary retinoblastoma. Previous investigations by Southern blot hybrid ization and PCR fragment-length analysis had revealed mutations in 48 patients. Here we report on the analysis of the remaining 71 patients. By applying heteroduplex analysis, nonisotopic SSCP, and direct seque ncing, we detected germ-line mutations resulting in premature terminat ion codons or disruption of splice signals in 51 (72%) of the 71 patie nts. Four patients also showed rare sequence variants. No region of th e RB1 gene was preferentially involved in single base substitutions. R ecurrent transitions were observed at most of the 14 CGA codons within the RB1. No mutation was observed in exons 25-27, although this regio n contains two CGA codons. This suggests that mutations within the 3'- terminal region of the RB1 gene may not be oncogenic. When these data were combined with the results of our previous investigations, mutatio ns were identified in a total of 99 (83%) of 119 patients. The spectru m comprises 15% large deletions, 26% small length alterations, and 42% base substitutions. No correlation between the location of frameshift or nonsense mutations and phenotypic features, including age at diagn osis, the number of tumor foci, and manifestation of nonocular tumors was observed.