X-ray sensitivity of fibroblasts from patients with hereditary retinoblastoma and their families.

The in vitro response to X-irradiation of cultured human fibroblasts was studied using a colony forming assay. A comprehensive reference range was established, giving a median D0 value of 98.5 cGy with an interquartile range of 86.5-110.5 cGy. Cells from 3 retinoblastoma family pedigrees were studied and the cell survival after exposure to X-rays was compared between affected (11 samples) and unaffected (26 samples) family members. No significant differences in response to ionising radiation were found between the controls, the affected and the unaffected members of the 3 families. The affected members had a median D0 of 97.5 cGy (interquartile range 87.5-107.5 cGy) and the unaffected members had a median D0 of 102 cGy (interquartile range 93-111 cGy). Thus radiosensitivity is not a useful marker for the detection of the retinoblastoma gene.