A deletion on chromosome

A deletion on chromosome 13 found in a group of affected
children, some of whom had additional congenital
abnormalities, enabled localisation of the retinoblastoma gene
to chromosome 13q14. The esterase D locus is closely linked to
the retinoblastoma locus and was used initially as a marker to
identify gene carriers in affected families. The retinoblastoma
gene has now been cloned and mutation analysis is possible.