Patients with 13q14 deletion have RB, and segregation of RB with markers (Q-banding and Esterase D) on chromosome 13 can be studied in some two-generation RB families.
A 153% value of ESD activity was found in the amniotic cells indicating unambiguously that the fetus was not monosomic for segment 13q14 and therefore not at increased risk for Rb.
The levels of expression of the viral genome in the Balb/c tumor and in the retinoblastoma line were determined by in vitro translation of RNA isolated from these cells and selected with appropriate restriction endonuclease fragments of Ad12 DNA.
Although a constitutional chromosomal deletion including 13q14 has been found to date in all retinoblastoma patients whose esterase D activity is 50 percent of normal, one female patient has been found who has 50 percent esterase D activity in all normal cells examined but no deletion of 13q14 at the 550-band level.
Evaluation of three families with hereditary retinoblastoma demonstrates close linkage of the gene for this tumor with the genetic locus for esterase D. These results assign the gene for the hereditary form of retinoblastoma to band q14 on chromosome 13, the same region which is affected in the chromosome deletion form of this eye tumor, and therefore suggest a common underlying mechanism in the pathogenesis of these two forms of retinoblastoma.
We tentatively conclude that induction of a retinoblastoma tumour requires the somatic inactivation of genes near the ESD locus including the remaining normal gene at the retinoblastoma (RB) locus.
The normal esterase D levels in this series of 51 retinoblastoma patients suggest that deletion of an esterase D locus is infrequent in retinoblastoma patients.