Prenatal Screening Part 2 Flashcards
What are the two methods of NIPS?
SNP based counting method (MPSS)
What were the original indications to offering NIPS?
advanced maternal age
abnormal serum screen (first or second trimester)
abnormal US
personal or family history of aneuploidy
What is SNP based NIPS?
focuses on special regions of interest in the genome (1% unique DNA)
now accepts twins and can report on zygosity
What is MPSS based NIPS?
looks at total genomic material without having to separate mother’s info from fetus
can distinguish between twins vs egg donor vs maternal DNA
What indications would be consistent for ordering a NIPS GENOME test?
couples with known translocation carrier status in chromosomes (not 13, 18, or 21)
can detect cryptic deletions/duplications >7Mb
still an ongoing study
What indications would be consistent for ordering a NIPS single gene disorders?
Advanced Paternal Age (50-55+)
de novo mutation panel
detects conditions that can only be seen in 3rd trimester US (or sometimes only after birth) including achondroplasia and osteogenesis imperfecta
What are the downsides of NIPS single gene disorder panels?
still self-pay only
not a lot of validation yet
requires both maternal and paternal samples as well
needs other testing to confirm
What is the only way to screen for neural tube defects?
quad screening
MSAFP
What makes NIPS possible?
apoptotic trophoblasts release fragmented placental DNA into maternal circulation –> maternal blood has mix of both maternal DNA and fetal DNA (~10%)
What factors could impact the accuracy of NIPS?
increased BMI
medications
time of sample did not allow for enough fetal DNA to be present
List the possible reasons for NIPS false positives.
fetal (confined placental mosaicism, co-twin demise/vanishing twin, fetal mosaicism)
maternal (malignancy, mosaicism)
lab (lab error)
other
What are the main factors that limit the detection of subchromosomal microdeletions/duplications?
size of variation
number of counts
fetal fraction
sequencing noise in the area
