Antenatal Screening and Chromosome Disorders Flashcards
When can chorionic villous sampling be carried out?
from 11.5 weeks
When can amniocentesis be carried out?
15+ weeks
What are the risks associated with chorionic villous biopsy?
miscarriage: 1-2%; confined placental mosaicism
What is the difference between the viability of tissues acquired in amnio and CVS?
in amniocentesis- poor whereas CVS ists good
What is the risk of miscarriage with amniocentesis?
0.5-1%
What is confined placental mosaicism?
placental tissue is fast growing tissue, so can have genetic abnormalities that the baby itself doesn’t have
What are the analyses avaible for looking at the whole genome?
standard karyotype; array CGH; fetal DNA in maternal serum; whole genome sequencing
What are the targeted genetic analyses?
point mutation testing; FISH; QF-PCR
What is the difference between standard karyotype and array CGH?
hundreds of base pairs in aCGH whereas millions of base pairs in karyotype
When is chromsome analysis carried out?
in metaphase
What is a single nucleotide polymorphism?
single base change
What is a copy number variation?
insertion or deletions of DNA material- polymorphism
When is FISH used?
when missing bit of chromosome is too small to see with aCGH
What is quantitative fluorescent PCR used for?
rapid counting of specific chromosomes
What is non-invasive prenatal testing used for currently?
sex determination and trisomy testing
What makes testing free fetal DNA in maternal circulation difficult?
only 10% of DNA comes from the fetus, the rest is materanl
What can cause there to be errors in looking for trisomy in NIPT?
confined placental mosaicism and DNA from cancers in mothers blood
What is the current first line genetic test for trisomy in an 18 week pregnancy?
aCGH on amniocentesis
What is a disadvantage of aCGH?
doesn’t pick up balanced translocation- need chromosome analysis
What is a Robertsonian translocation?
two acrocentric chromoeomes stuck end to end
What is an acrocentric chromosome?
where the centromere is located near the end of hte chromosome
What is aneuploidy?
too many or too few chromosomes
What is a reciprocal translocation?
exchange of genetic material between non-homologous chromosomes
Why is doing a genetic test on the fetus good to be as early as possible?
changes availability of options for TOP
