Expression of fragile sites in patients with retinoblastoma, their parents, and unaffected siblings: a study of ten families.

The expression of fragile sites (FS) in the blood lymphocytes of 54 individuals, including 11 retinoblastoma (Rb) patients, their clinically healthy family members, and corresponding age- and sex-matched controls is presented. 5-fluorodeoxyuridine (5-FdU) and caffeine were used for FS induction. Enhanced expression of fra(13)(q13.2) was observed in the patient group as compared with controls. One of the patients had a constitutional del(13)(q14.2q21.2). In this individual, only the nondeleted homologue expressed the fra(13)(q13.2). Expression of fra(13)(q13.2) in two of the patients' unaffected younger siblings of different families showed statistically significant values. The possible relation between enhanced expression of FS and the inheritance of a genetic predisposition to Rb requires further examination.