RB1 DELETION IN GONADOBLASTOMA IN AN XY FEMALE

Cytogenetic studies of normal and tumor cells in a patient with gonada l dysgenesis and bilateral gonadoblastoma were performed. The karyotyp e was 46,XY in peripheral blood lymphocytes and skin fibroblasts. The conserved region of the SRY gene was detected by polymerase chain reac tion amplification. Sequencing of this region did not reveal any alter ations. A 46,XY chromosome constitution was observed in the right gona doblastoma, but a partial deletion of chromosome 13 was present in the left tumor. This deletion included band 13q14, where the retinoblasto ma gene is mapped. The study of the polymorphism of the variable numbe r of tandem repeats region in intron 17 of the RB1 locus disclosed los s of heterozygosity in both the left tumor, which showed the deletion of chromosome 13, and in the right tumor, where no chromosome alterati ons of chromosome 13 were detected. In situ hybridization covering 130 kb of RB1 showed that a partial deletion of one of the RBI alleles ha d occurred in the right tumor. Since the deletions affected different alleles in each tumor, independent events must have been involved in t he development of the tumors. These findings point toward a significan t role of RE 1 in the development of gonadoblastoma.