الفهرس 
DOWN SYNDROMEOnly 14 pages are availabe for public view
 |  | from | 138 |  |  |
| | | from | 138 | | |
Abstract
Down syndrome, is the most common chromosomal aneuploidy, it affects up to 1 in 750 live births. It is caused by an extra copy of chromosome 21 or a triplication of part of it.
Current invasive prenatal diagnostic methods for fetal chromosomal aneuplodies, such as amniocentesis or chorionic villus sampling, pose a finite risk to the fetus. Noninvasive screening methods, including nuchal translucency and maternal serum biochemical screening typically detect the associated epiphenomena instead of the core genetic abnormalities of chromosome dosage imbalance and are not diagnostic in nature
For many years, research in non invasive testing has focused on the isolation and analysis of the rare fetal nucleated cells and the cell free fetal DNA in the plasma of pregnant women however, many problems appeared in their use.
The demonstration of detectable circulating fetal RNA in maternal plasma has led to the development of new noninvasive prenatal diagnostic opportunities. Unlike fetal DNA measurements in maternal plasma, quantitative analysis of circulating fetal RNA has the advantage of being applicable to all pregnant women irrespective of fetal gender or genetic polymorphism status.
In the present study we tried to isolate chromosome 21 encoded mRNA, to detect and measure the level of expression of C21ORF105 gene in maternal plasma in trisomy 21 pregnancies.
The cases studied were 40 high risk pregnant women who were undergoing amniocentesis. They were divided into 2 groups, the first group consisted of 13 patients who had either abnormal triple test and /or nuchal translucency, and the other group consisted of 27 patients with normal triple test and nuchal translucency but had previous history of delivering a Down syndrome infant. The control group included 10 non pregnant women, 4 of them are affected by trisomy 21.
Karyotyping was done for all amniotic fluid samples which revealed normal karyotype in 38 cases(95%),two cases with abnormal karyotype(5%), one with trisomy 21 (2.5%) and the other with trisomy 18 (2.5%).
Blood samples for RT-PCR were collected immediately before the amniocentesis procedure which was done between 14 and 17 weeks. RNA was extracted from maternal and control group plasma followed by amplification of the desired gene by RT-PCR, detection by agarose gel electrophoresis and semiquantitation using the gel documentation and analysis system.
C21ORF105 gene was not detected in the plasma of the control group even in the Down syndrome patients while it was detected in samples from all pregnant women which prove that the gene we targeted is placental in origin and expresses the genetic status of the chromosome 21 of the fetus so it can be reliably used in prenatal diagnosis. In addition, the semiquantitative measurement of C21ORF105 revealed a 2.6 fold increase in the band density in the patient with Down syndrome pregnancy than in the other patients.
The results of both RT-PCR and karyotyping were parallel with each other, which indicate that this method is a good specific test for prenatal diagnosis of Down syndrome, however, sensitivity cannot be evaluated in this study as we had only one case of Down syndrome.
Triple test and nuchal translucency measurement were done for the patients group. A highly statistically significant difference was detected as regards triple test on comparing between patients who had normal karyotype versus those with abnormal karyotype including trisomy 21 and 18 (P<0.01) and a statistically significant difference was detected between the patients as regards the measurement of the nuchal translucency (P<0.05)
Correlation studies between the semiquantitative measurement detected by PCR for C21ORF105 gene and the level of the different biochemical markers, the nuchal translucency and the maternal age were done. No statistically significant correlation was detected except for the β-hCG.
The gene C21ORF105 may be a good candidate for noninvasive prenatal diagnosis of Down syndrome as it is encoded by chromosome 21, expressed in healthy early placental tissue, detectable in maternal plasma during early pregnancies and it is over expressed by the placenta in trisomy 21 pregnancies.