Use of the RB1 cDNA as a diagnostic probe in retinoblastoma families.

Use of an intragenic BamHI restriction fragment length polymorphism within the 5' end of the retinoblastoma gene (RB1) provided improved genetic counselling for five familial and ten non-familial retinoblastoma patients and their relatives. All other polymorphic probes within RB1 were uninformative in three families, and accuracy of diagnosis was improved by use of this polymorphism in two families. In 10/14 informative constitutional DNA-RB tumor DNA pairs, a reduction to homozygosity allowed identification of the RB1 allele at risk to carry a germline RB1 mutation.