The Methodology On Prenatal Screening And Gene Diagnosis For Down's Syndrome

Objective: (1)To explore a technological system suitable for the Down' s syndrome prenatal screening in Yunnan province, using maternal serum markers. (2)To investigate the genetic polymorphism of two STR loci on chromosome 21 in Kunming Han population as well as its application in DNA testing for Down' s syndrome. Methods: (l)Three maternal serum markers, PAPP-A, AFP and Free B-hCG of 2453 cases were quantitatively detected by the time resolved fluorescent immunoassay technology; (2)The genomic DNA extracted from 100 unrelated individuals of Han nationality in Kunming and 2 Down' s syndrome patients were amplified by PCR technique. The PCR products were analyzed using polyacrylamide gel electrophoresis (PAGE), followed by silver staining. And the allele size was detected by Image Analysis System. Results: (1) 83 cases in 2453 pregnant women were screened as high risk for Down' s syndrome, and 1 was verified as trisomy 21 through prenatal diagnosis in 47 high risk pregnant women who accepted amniocentesis. (2) The normal medians of maternal serum markers on every gestational week in Kunming population were obtained. The medians of PAPP-A, AFP and Free B-hCG have no significant differences (P>0. 05) between our population and those of Finnish and British population offered by PE company. (3) The incidences of spontaneous abortion, missed abortion, fetal malformation, pregnant with thyroid malfunction in the PAPP-A lower group were significantly higher than those of the control group between 8 and 14 gestational weeks. Oppositely, in the PAPP-A evaluated group, the incidences of pregnancy-induced hypertension and twin pregnancy weresignificantly higher than those in the control group; Between 15 and 20 gestational weeks, the incidences of missed abortion and intrauterine fetal demise in the AFP lower group were significantly higher than those of the control group. In the AFP evaluated group, the incidences of spontaneous abortion, missed abortion, intrauterine fetal demise, fetal malformation, pregnancy-induced hypertension, twin pregnancy, twin pregnancy with one dead fetal were significantly higher than in the control group; Between 8 and 20 gestational weeks, in the Free B-hCG lower group, the incidences of spontaneous abortion, missed abortion, intrauterine fetal demise, fetal malformation were significantly higher than in the control group; In the Free 3 -hCG evaluated group, the incidences of fetal malformation, pregnancy-induced hypertension twin pregnancy were significantly higher than in the control group. (4) The genetics data including allele numbers, gene frequencies, genotype frequencies, heterozygosities and the polymorphic information contents (PIC) were observed in the studied population. In the meantime, the molecular diagnosis for Down' s syndrome using DNA testing method was successfully verified by the cytogenetic karyotyping in two patients. Conclusions: (1) The medians and normal reference intervals of maternal serum markers: PAPP-A, AFP and Free B-hCG of each gestational week in Kunming population were established, offering reference data for other local prenatal screening programs. (2) Combined test of PAPP-A, AFP and Free B-hCG may be an effective and easily-accepted technique for Down' s syndrome screening to the first trimester and second trimester pregnant women. (3) Excessive higher or lower values of PAPP-A, AFP and Free B-hCG imply certain abnormal pregnancies, and the test results will be benefit to clinical prognostic evaluation . (4) D21S1411 and IFNAR are two high polymorphic information content (PIC) loci. These two loci are valuable genetic markers in the molecular diagnosis for Down' s syndrome.