Application of linkage analysis to genetic counselling in families with hereditary retinoblastoma.

Six families with retinoblastoma in more than one member were investigated with DNA markers linked to the retinoblastoma locus because direct analysis had not disclosed the gene defect. In all of the families we could identify the affected chromosome and predict the genetic risk with a high level of confidence (90 to 99%). In one patient the test helped to detect tumour development earlier than usually possible. Several subjects were found not to carry a mutation, thus obviating frequent ophthalmological examinations under anaesthesia as would be necessary otherwise. These results show that linkage analysis can be successfully applied to genetic counselling in families with hereditary retinoblastoma.