[Establishment of lymphocyte cell lines with abnormal chromosome karyotypes and its application in external quality assesment for chromosome karyotype analysis].

OBJECTIVE: To develop chromosome abnormal karyotype quality control cell and to explore the external quality assessment (EQA) method for chromosome karyotype analysis. METHODS: The chromosome abnormal karyotype quality control cells were prepared by EB virus (EBV) transfection of human B lymphocyte strain establishment and were distributed to participating labs for EQA test of chromosome karyotype analysis project at appointed time. The evaluation results were obtained through 4 grades scoring. RESULTS: Six kinds of chromosome abnormal karyotype quality control cells were initially developed, the karyotypes of which were 46,X, t(Y;5)(q12;q21), 46, XY, 15p +, 46, XX, t(13;18)(q12;q21), 46, X, r(Xp), 46,X,t(Y;Y), 46,XX,t(9;20)(p13;p13) respectively. In the external quality assessment, feedbacks from the participating labs on the sequencing results of the six kinds of quality control cells showed that the wholly overlapping rate were 82.1%, 92.0%, 84.6%, 80.8%, 86.2%, 74.1% and the wholly deviation rate were 10.7%, 8.0%, 11.5%, 19.2%, 13.8%, 18.5%. The overall wholly overlapping rate, partial overlapping rate, partial deviation rate and wholly deviation rate turned out to be 83.2%, 0.6%, 2.5% and 13.7% respectively. CONCLUSION: The misdiagnose rate of chromosome karyotype analysis is rather high and regular external quality assessment is necessary to achieve dynamic information and improve diagnosis quality.

Novel real-time PCR assay for rapid prenatal diagnosis of Down syndrome: a prospective study of 563 amniocytes.

OBJECTIVE: To explore the possibilities of a novel real-time PCR assay for rapid prenatal diagnosis of Down syndrome in clinical settings. DESIGN AND METHODS: This duplex real-time PCR assay is based on relative quantification of DSCR4 gene on chromosome 21 by using RABIF gene on chromosome 1 as a reference. For each sample, the differences in threshold cycles between DSCR4 and RABIF genes (Delta Ct, DeltaCt) were detected, and a calibrated DeltaCt value (DeltaDeltaCt, DeltaCt (sample)-DeltaCt (internal control)) was analyzed. Overall, 563 amniotic fluid samples from patients were blindly tested for fetal chromosome analysis and their DeltaDeltaCt values were evaluated according to the karyotyping results. RESULTS: Chromosome analysis revealed that 12 fetuses had trisomy 21 and 551 others were normal in chromosome 21. The DeltaDeltaCt values of trisomy 21 fetuses were significantly lower than those of normal ones (p-value<0.001) and no overlapping was shown: lower than -0.49 for trisomy 21 and above -0.30 for a normal one. CONCLUSIONS: DeltaDeltaCt value could be used as a direct diagnostic index in real-time PCR assay; this novel assay is applicable for rapid prenatal diagnosis of Down syndrome in clinical settings.