PRENATAL-DIAGNOSIS OF PARTIAL TRISOMY THROUGH IN-SITU HYBRIDIZATION ON AMNIOCYTES WITH WHOLE CHROMOSOME AND CENTROMERE-SPECIFIC DNA PROBES - A CASE-REPORT

BACKGROUND: DNA probes specific for whole chromosomes or portions of c hromosomes can provide important information to aid the clinician in m anaging pregnancy and the geneticist in relaying accurate recurrence r isk information to the patient. CASE: In this case, sonography was ord ered because of a low fundal height in a 29-year-old primigravida at 3 5 weeks' gestational age; it revealed major fetal anomalies. A small s upernumerary marker was seen in some cultured amniocytes. Metaphase sp reads were analyzed by means of fluorescence in situ hybridization usi ng a centromere probe specific for chromosome 22 and a whole chromosom e probe for the 11 chromosome. In situ hybridization showed that the m arker chromosome was a derivative of chromosome 22 with 11q material a ttached near the centromere. The fetal karyotype was 47,XY,+der(22) t( 11;22)(q23.3;q11.2)mat. The mother was later found to be a balanced tr anslocation carrier. CONCLUSION: It was possible to offer rapid prenat al diagnosis for this family using interphase analysis with the 22 cen tromere probe. The patient had chorionic villus sampling, and DNA prob es were used to analyze cells directly from the biopsy. The signal rep resenting the supernumerary marker was not observed. Karyotype analysi s later showed that the fetus was normal but a translocation carrier. This report illustrates that rapid in situ hybridization can provide i mportant information in known cases of translocation carriers.