Retinoblastoma, deletion 13q14, and esterase D: application of gene dosage effect to prenatal diagnosis.

Esterase D (ESD) gene dosage studies were performed on amniotic cells from a fetus at risk for del 13q14. The mother was a balanced carrier of an insertion in chromosome #20: 46,XXins(20;13)(p12;q1307q14.3). She had already given birth to a monosomic child with retinoblastoma (Rb) and to a phenotypically normal child trisomic for the same 13q14 segment. Both sibs displayed the expected proportionate gene dosage effects for ESD. 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 mother delivered a phenotypically normal child who was confirmed to be trisomic for segment 13q14 by cytogenetic analysis and by gene dosage studies for ESD in cord blood cells and in lymphoblastoid cells.