General topics in genetics Flashcards
In your practice, for whom do you recommend cell free DNA screening?
All patients
How do you counsel the low risk patient who desires cell free DNA screening?
Lower positive predictive value in low risk population
What is the sensitivity of cell free DNA for trisomy 21, 13 and 18?
99% ————— SNOUT - sensitivity rules out disease. What is the probability that the test will be positive if the disease is present.
What is the specificity of cell free DNA for trisomy 21, 13 and 18?
99% ————– SPIN - specificity rules in disease. What is the probability that the test is negative if disease is not present.
What is the positive predictive value of cell free DNA screening of Trisomy 21?
High risk population - 84% Low risk population - 37%
What is the negative predictive value of cell free DNA for Trisomy 21?
99%
When you perform an amniocentesis for genetic testing, what testing do you order?
FISH Direct FISH Karyotype CMA Whole exome sequencing
What is chromosomal microarray?
it is whole genomic sequencing using DNA primers to bind complimentary DNA. More or less binding noted in color with copy number variants. Cannot detect balanced translocation
What is the likelihood of an abnormal microarray result if the fetus has an anomaly and a normal karyotype?
6%
What is the significance of a cell free DNA result that states low fetal fraction?
Associated with increased risk of aneuploidy. __________________ -3-13% normal fetal fraction -fetal fraction is needed to calculate risk of aneuploidy
Indications for invasive diagnostic testing?
-Patient desire -Advanced maternal age -Abnormal genetic screening -Anomaly noted on ultrasound -Maternal or paternal history of translocation
Describe how you perform amniocentesis
Using continuous ultrasound guidance, a 20-22G spinal needle is used to puncture the skin, underlying muscle and fascia and uterine wall until in the intramniotic space that is free of cord and fetal parts after which the needle guide is removed and syringe is placed. The firs 1-2 ml of fluid obtained are discarded. No more than 2 attempts.
At what gestational age can you perform amniocentesis?
15 weeks gestation
What are the risks of amniocentesis?
Infection, alloimmunization, bleeding, rupture of membrane 1-2% Pregnancy loss 0.2-0.3% Lack of cell culture growth 2%
Describe how you perform CVS?
Under continuous ultrasound monitoring, I use an 18-20G spinal needle to puncture the skin and underlying muscle, fascia and uterine wall until in the placental space after which the needle guide is removed and tissue media filled syringe is placed and constant pressure is placed. The placenta is biopsied along a trajectory with back and forth movements for at least 3 times. The syringe and needle are removed simultaneously while maintaining pressure on the syringe.
How do you intepret soft marker in the setting of a normal NIPT?
