Confirmation of a balanced chromosomal translocation using molecular techniques.

Investigation of a couple, who had produced three babies with cri du chat syndrome, showed initially that the mother had an apparent deletion of chromosome 5. It seemed likely that she had a balanced chromosomal translocation but it proved impossible to detect the second chromosome involved using routine cytogenetic methods. Molecular techniques using quantitative hybridization dosage studies were performed and these showed that the mother had a double dose of DNA in the suspected deleted area of chromosome 5. Further studies, using in situ hybridization techniques, revealed that the missing segment of chromosome 5 had translocated onto the short arms of a C group chromosome and further analysis of prometaphase chromosomes showed the presence of a balanced translocation, 46,XY,t(5;9)(5qter----5p14.1::9p22----9pter;9 qter----9p22::5p14.1----5pter). As a result of these findings, it was possible to offer prenatal diagnosis to the patient in future pregnancies, by detecting the presence of a balanced or unbalanced translocation in the fetus using molecular and cytogenetic techniques.