Application of different technologies for distinguishing true and pseudo mosaicisms during prenatal diagnosis

Objective To use different technologies to distinguish true and pseudo mosaicisms among cultured amniocytes in order to attain more accurate diagnosis. Methods With informed consent, 20 mL of amniotic fluid was obtained from pregnant women at between 18 to 24 gestational week. Each amniotic fluid sample was processed as two separate lines for the culturing, observation, harvesting and analysis. All procedures were conducted conforming to the Technology Standards of Cytogenetic Prenatal Diagnosis of Fetal Chromosome Abnormalities issued by the Ministry of Health in 2010. Umbilical cord blood, fluorescence in situ hybridization （FISH）, single nucleotide polymorphism array （SNP-array） and flow cytometer were applied when necessary. Results Among 3910 cases, 128 （3. 3%） were detected as mosaicisms. Further analysis with the above technologies has verified 6 cases as true mosaicisms and the remaining 120 as pseudomosaicisms. For one case detected by karyotype analysis as 47, XXY/46, XY, the ratio of different cell lines was confirmed by FISH as 1 ： 2. Another case, detected by karyotype analysis as 47, XX, ＋ mar/46, XX （1 ： 1）, was verified by SNP-array as 18p duplication. A suspected polyploidy mosaicism was rejected by flow cytometry and cord blood karyotyping. Conclusion Two separate cell cultures are important for distinguishing true and pseudo mosaicisms. Combined FISH, SNP-array and flow cytometry can attain more reliable and accurate diagnosis for mosaicisms. Key words: Prenatal diagnosis;  Cell culture;  Mosaicism;  Fluorescence in situ hybridization;  Single nucleotide polymorphism array