Mutation of the RB1 gene caused unilateral retinoblastoma in early age

Fluorescence in situ hybridization (FISH) was applied for the detection of the retinoblastoma tumor-suppressor gene deletion on retinoblastoma tumor c ells obtained from the unilateral tumor of a 3-month-old boy, Both retinobl astoma tumor cells and peripheral lymphocytes of the patient showed one hyb ridization signal per cell at the retinoblastoma-1 locus, indicating that o ne copy of the gene was deleted. Peripheral blood lymphocytes obtained from the patient's parents had two copies per cell for the gene. Retinoblastoma nuclear phosphoprotein expression could not be detected in the tumor tissu e. No copy number alterations were detected with ten different centromeric DNA probes in the tumor cells. The deletion at the RB1 locus detected by FI SH suggested that this gene alteration was heritable. The parental peripher al blood lymphocytes did not show the loss of the gene; thus the first dele tion may have taken place in either of the parental germ cells. The second somatic mutation of the RB1 gene was probably under the detection limit of FISH. The second allelic alterations were detected by using the polymerase chain reaction for all exons of the retinoblastoma gene. (C) 2000 Elsevier Science Inc. All rights reserved.