The gene related to retinoblastoma (Rb gene) can be considered a model human tumor suppressor gene and was assigned to band 13q14, together with the esterase D (ESD) gene.
When the occurrence of retinoblastoma is based on a chromosome deletion, red cell esterase D might be a potential tumor marker for diagnosing retinoblastoma.
Studies utilizing multiple polymorphic markers, (ESD isoenzymes, restriction fragment length polymorphisms and karyotypic heteromorphisms) have shown that a somatic change from heterozygosity in constitutional cells to homozygosity in RB tumors occurs frequently for chromosome 13q but not for other chromosomes.
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.