Sister chromatid exchanges in patients with retinoblastoma

Spontaneous and mitomycin C(MMC)-induced sister chromatid exchanges were studied in 11 patients with retinoblastoma and 7 normal controls. Spontaneous rates were similar in patients and in controls. The MMC-induced rate was found to be significantly higher in bilaterally affected patients than in controls. It is suggested that this increase may be due to a DNA repair deficiency. However, it is not possible to clarify whether this abnormality is associated with the retinoblastoma gene or with another factor acting on the degree of expressivity of the disease in gene carriers.