Prenatal diagnosis of trisomy 9: cytogenetic, fish, and DNA studies.

A cytogenetic survey and follow-up studies were performed in eight cases of full, mosaic, and pseudomosaic trisomy 9 prenatally diagnosed among 36,213 prenatal samples in our department between August 1970 and July 1996. Besides conventional chromosome analysis, interphase fluorescent in situ hybridization (FISH) was employed. FISH turned out to be a rapid and accurate method for verification of trisomy cell lines and could provide additional information to the prenatal cytogenetic results. FISH also enables the study of uncultured specimens of amniotic fluid, not accessible for traditional cytogenetic analysis. In three cases, retrospective DNA analysis showed the supernumerary chromosome 9 to be of maternal origin. The disomic cell lines in both mosaic trisomy 9 cases showed maternal uniparental disomy.