Skin fibroblasts from a D-deletion type retinoblastoma patient are abnormally X-ray sensitive

Abstract

RETINOBLASTOMA is a rare malignant eye tumour which appears spontaneously or occurs in genetically predisposed persons^1–3. The latter group is composed of patients who inherit the tumour with a dominant mode of transmission (80–90% penetrance) (referred to as the familial type) or those who bear a deletion in the long arm of chromosome 13 (13q-) (referred to as the D-deletion type). When this deletion is present, it is observed in many somatic cells and is often associated with structural defects such as microcephaly, micropthalmia and several skeletal and genitourinary abnormalities^3,4. Survivors of the genetic forms of retinoblastoma have an increased risk for the development of cancers at other sites, while patients who survive the sporadic type do not^2–6. A single genetic locus is unlikely to predispose many somatic cells to tumour formation unless a fundamental molecular defect—for example, related to DNA repair—is present. To investigate this hypothesis, we have examined the in vitro X-ray sensitivity of skin fibroblast strains derived from three retinoblastoma patients—a pair of twins with the familial type accompanied by no gross chromosome abnormalities, and a patient with the D-deletion type. We also used two normal fibroblast strains and a strain from a patient with ataxia telangiectasia. We found that the strain derived from the D-deletion retinoblastoma patient was significantly more radiosensitive than the two normal strains, but not as sensitive as that from the ataxia patient.