Prenatal Chromosomal Analysis Lecture Notes PDF

Biological and chemical Analytics (BIOT303) Faculty of Biotechnology Biological and Chemical Analytics Lecture 10: Prenatal chromosomal analysis Dr. Rana A. Youness Head of Mo...

Biological and chemical Analytics (BIOT303) Faculty of Biotechnology Biological and Chemical Analytics Lecture 10: Prenatal chromosomal analysis Dr. Rana A. Youness Head of Molecular Genetics Research Team (MGRT) E-mail: [email protected] Office: S1-610 Office Hours: Thursday 12-1 pm Intended Learning Outcomes (ILOs): By the end of the lecture and after reading the appropriate text books, the student should be able to understand: Recall sources of specimens for chromosomal analysis Define Prenatal chromosomal analysis Differentiate between different types of Prenatal chromosomal analysis techniques Understand the procedure of chorionic villus sampling (CVS) Understand the procedure of Amniocentesis Understand the procedure and significance of Nuchal Translucency Ultrasound Understand the principle of preimplantation genetic diagnosis or preimplantation genetic testing 2 Sources of specimens for chromosome analysis 3  Preimplantation genetic screening (PGS) or preimplantation genetic testing PGT-A or PGT-SR PGS screens embryo cells for the normal chromosomal number prior to implantation & reveals diseases such as Down’s syndrome, Turner syndrome,..etc PGT-A: preimplantation genetic testing for Aneuploidy PGT-SR: preimplantation genetic testing for structural chromosomal rearrangements 1- IVF of the egg with a sperm in the lab 2- Resulting embryos are incubated for 3 days till they grow to approximately 8-10 cells each 3- PGS is a step added to the IVF cycle. PGS will be performed guided by powerful microscope and tiny hollow glass needle to remove a single cell. 4- Analysis of the obtained single cell can foretell the embryos future. So, PGS enables the experts to choose which embryos will be implanted in the mother. 5- Using this info, embryos are selected and are being implanted into the mother  Preimplantation genetic diagnosis (PGD) or preimplantation genetic testing (PGT-M) o First reported in 1990s o Used in conjunction with IVF o Genetic testing of embryos created in vitro for heritable genetic conditions o Prevent transmitting serious genetic disorders o Prevention of 5-10% of all cancers o Combination of advances in genetics and assisted reproductive technology PGD or PGT procedure PGD Genetic testing can give us information about specific chromosomal disorders & specific structural rearrangements  Prenatal chromosomal analysis This is important in identifying human chromosome abnormalities and can be done in three ways: 1. Chorionic villus sampling (CVS) 2. Amniocentesis 3. Blastomeres (after in vitro fertilisation) The three are considered diagnostic techniques. They are invasive and can provide a specific answer to whether or not a specific disorder is associated with a chromosome abnormality 8  Chorionic villus sampling (CVS) o 11-14 weeks of pregnancy o Sample of tissue is taken from the placenta o The chorionic villi is the name of the tissue that will eventually become the placenta oFine needle is passed through the abdomen or into the uterus to take the sample  Amniocentesis o 15-20 weeks of pregnancy o Needle pushed through the abdomen and then through the uterus into the pocket of amniotic fluid (AF) o AF (10-20 ml) contains cells shed from the foetus that can tested (If the 20 ml is not enough, we can culture the cells for further testing) o It should not be stained with blood  Nuchal Translucency Ultrasound ❑ Ideally performed between 11 & 13 weeks. ❑ NT thickness is a measure of the amount of fluid at the back of the foetal neck ❑ 3 measurements to the nearest 0.1 mm are advised ❑ The thickness is higher in Down’s pregnancies during screening period  Nuchal Translucency In Turner Syndrome a female miss a Ultrasound complete X chromosome Normal Down Syndrome Turner Syndrome 1.5 mm 3.4 mm 10 mm Thickness > 2.8 mm sets high risk for Down Syndrome Cell-free fetal DNA (cffDNA) o Non-invasive prenatal screening (NIPT) for fetal aneuploidies o Circulating cell free fetal (cff) DNA present in maternal blood o Detected as early as 7 weeks of gestation o Non-invasive prenatal diagnosis (NIPD) for some X-linked disorders & Rh incompatibility (Rh- mother; Rh+ baby)  From conventional cytogenetics to molecular cytogenetics: advances in medicine Cytogenetic approaches like for example Karyotype G Banding are applied for detection of chromosome abnormalities. For instance, the gross genomic variations that involve more than 3-5 megabases. The molecular cytogenetic techniques are used for refinement of variations detected by cytogenetic analysis and for identification of subtle genomic variations at chromosomal or even at sub-chromosomal levels achieving the highest resolution of approximately 1Kbp The molecular cytogenetics aren’t used for routine determination, instead they are used as 2nd stage test because they might take longer time periods, larger cell number and higher cost. Thank You 16