Lect 10: Prenatal Genetics Flashcards
Reasons for prenatal testing
- a parent is a carrier of a structural chromosome rearrangement or there is a previous child with one
Non-invasive example is MSAFP & ultrasound. When is it performed?
around 18 weeks of gestationn
Why is an ultrasound useful?
- to verify viability
- to detect multiple pregnancies
- to determine the gestational age
- to identify possible abnormalities - a) NUCHAL TRANSLUCENCY…thickness >1.3 is DownSyndrome
b) Cleft palate
c) neural tube defects
Non-invasive: MSAFP
draw blood from mom to check for alphafetoprotein which is produced by the fetal liver.
==>sensitive to mom’s weight, age and diabetic status
When is MSAFP testing done?
16 - 18 weeks
What do low or high levels of MSAFP mean?
Low levels: Down Syndrome and other chrom abn
High levels: Open Neural Tube Defect *Not sensitive Only used for risk assessment, not a diagnosis
Maternal serum Quad Test
checks out 4 pregnancy related proteins: AFP, hCG, unconjugated estriol, dimeric inhibin-A
together they are sensitive to picking up Down Syndrome
Integrated Prenatal Testing is done at what gestational stage?
10 - 13 weeks gestation;
– PAPP-A is assoc with higher risk of DS
Non-invasive prenatal screening is done at which gestational age?
10-22 weeks
What is NIPS/NIPT?
Mom’s blood is tested to retrieve free floating DNA from her and the fetus. Then you use DNA sequencing technology to match the fragment with the chromosome from that fetus. Any increase or decrease in total value of a chromosome suggests aneuploidy. NOT DIAGNOSTIC/ ONLY GIVES RISK. Need to confirm
Invasive Testing includes Amniocentesis. When is it done?
16-18 weeks gestation but early testing can be done starting ar 13 or 14 weeks.
Amniotic Fluid AFP
Low levels: chromo abnormalities, confirmed by karyotyping
High levels:higher risk of ONTD, confirmed by Acetylcholinesterase
Chorionic Villous Sampling
you take the cells from the placenta instead of the fetus. It is done 10 - 14 weeks
Confined placental mosaicism occurs where the placenta carries a mutation but not the fetus . If CVS is done and this mutation is detected, it could be misinterpreted as fetal
So this can be a drawback
What is the advantage of CVS testing
it is done EARLY!!!!
Assisted Reproductive Technologies
IVF, ICSI, ZIFT, Donor egg or sperm
Polar body analysis for iVF
done on the oocytes. If the first polar body is positive for the CF mutation the the corresponding egg is not expected to have the mutation. If it is vice versa then the egg would not be used
Prenatal Genetic Diagnosis
screening technique for embryos
