Down syndrome is one of the most common congenital genetic disorders and is also the most common reason for mental retardation. Risk for Down syndrome is usually determined by noninvasive tests. If high risk is detected, then invasive tests are performed to confirm or deny the presence of Down syndrome. Invasive tests can cause different complications, including miscarriage. The latter is the main driving force for scientists attempting to find new noninvasive methods to get to fetal genetic material. The goal of our research was to validate a noninvasive screening test for determination of presence or absence of Down syndrome in a pregnant woman’s peripheral blood sample and test it on a small Slovenian population of pregnant women. Fetal DNA, which is also present in maternal blood, is differentally methylated in certain regions on the 21st chromosome. Fetal target regions are hypermethylated in comparison to corresponding maternal regions. We separated fetal target regions from maternal ones with the method of methylated DNA immunoprecipitation. The difference in copy numbers between Down syndrome and healthy cases was detected with real time polymerase chain reaction. The results were then analysed with a certain algorithm. We tested 26 blood samples, of which one had been confirmed positive for Down syndrome with amniocentesis. In our laboratory we managed to correctly classify 13 cases, the positive one as well, with few adjustions to the protocol. During the study we had some problems with a certain target region, which is why we decided to exclude it from the algorithm. After the exclusion more convincing and clearer results were obtained.
We believe that the validated method has potential to be used in clinical practice, but still needs to be tested on a larger population under standardized conditions. It can be performed relatively early in pregnancy, is easy to do, cheap and fast.
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