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Block 1 Week 4 > Genetic Counseling > Flashcards

Genetic Counseling Flashcards

1
Q

What are the 3 common prenatal screening tests?

A

1) maternal serum screening
2) non-invasive prenatal screening (NIPS)
3) ultrasound

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2
Q

what are the two primary diagnostic tests done prenatally?

A
  • Chronic Villus Sampling

- Amniocentesis

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3
Q

What 5 things can be done with CVS and Amnios?

A

1) Karyotype
2) Amniotic Fluid (AF-AFP)
3) Microarray
4) Single gene/multi-gene panel testing
5) whole exome

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4
Q

what is the difference between screening & diagnostic testing?

A

screening identifies risk for certain birth defects; diagnostic testing definitively identifies trisomies

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5
Q

screening test tell you what?

A
  • identifies risk for certain birth defects

- can get inherent false negatives & positives

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6
Q

what does diagnostic testing tell you?

A
  • definitively identifies trisomies & other types of chrom. disorders & single gene disorders
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7
Q

6 hormones checked during Prenatal screening and testing

A

1) hCG (1st & 2nd trimester)
2) PAPP-A (1st)
3) AFP (2nd)
4) DIA (2nd)
5) uE3 (2nd)
6) inhibin

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8
Q

3 types of maternal screening involved in the Ca state screening program? (3)

A

1) sequential integrated screening + NT (1st & 2nd)
2) serum integrated screening (1st & 2nd)
3) qua marker screening (2nd trimester)

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9
Q

Sequential integrated screening

A
  • occurs in the 1st and 2nd trimesters
  • done inconcordance w/ Nuchal Translucency (NT)
  • highest detection rate for down syndrome
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10
Q

What dos the maternal screening program look for?

A
  • looks at different pregnancy related proteins in mom

- depending on level (adjusted for weight, race, age, diabetets, and smokers) it will adjust the risk for mom & baby

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11
Q

Nuchal Translucency (NT)

A
  • critical component of sequential integrated screening
  • measures fluid that collects behind fetus’ neck
  • as mm of fluid increase, so does % of risk
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12
Q

in Nuchal Translucency (NT) whats considered a screen positive?

A

-anyone 3mm or higher considered screen positive, have greater than 1 in 5 chance of chrom abnormalities

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13
Q

What look for in the sequential integrated screen when screening for DS? (7)

A
  • look at multiples of median (MoM) for all 6 hormones + NT
  • want all avg to be 1.0
  • Pattern of MoM for DS:
    1) HCG 1st elevated
    2) pap A low
    3) AFP low
    4) HCG 2nd high
    5) unconjugated estriol low,
    6) inhibin high
    7) NT to be increased
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14
Q

Other reasons why sequential integrated screen can come back + for DS? (2)

A

1) normal variation in mama

2) error in dating of pregnancy (if off by more than 2 weeks test won’t be accurate)

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15
Q

What does a high HCG & inhibin indicate?

A
  • increase risk for pregnancy complications;

- early labor pre-eclampsia, palcental functioning etc

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16
Q

For trisomy 18 positive screen what do we look for in the sequential integrated screen?

A

-all 6 hormones & NT to be below avg

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17
Q

For Smith-Lemli-Optiz syndrome positive screen what do we look for in the sequential integrated screen?

A

1) unconjugated estriol, if lower than .3 are screen positive

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18
Q

For Neural Tube disorder positive screen what do we look for in the quad screen?

A

-the AFP value, average is 1.0, if have 2.5 or greater will be screen positive

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19
Q

Other reasons to screen positive for Neural Tube disorders w/ quad screen? (5)

A

1) Dating of pregnancy
2) Mutliples
3) Vaginal Bleeding
4) Placental issues
5) Normal variation

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20
Q

What do all 3 screens look for? (4)

A

1) Trisomy 21
2) trisomy 18
3) open neural tube/ abdominal wall defects (won’t detect closed ones)
4) Smith-Lemin-Optiz syndrome

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21
Q

What do State Approved prenatal diagnostic centers do if screen positive?

A

1) genetic counseling
2) ultrasound
4) chorionic villus sampling-if 1st tri referral (karyotype or microarray)
5) amniocentesis (karyotype or microarray)
6) NIPS

22
Q

NIPS? What does it screen for (4)?

A
  • noninvasive prenatal screening (or Cell Free DNA)
  • screen for
    1) DS
    2) trisomy 18
    3) trisomy 13
    4) sex chrom aneuploidy
23
Q

How does NIPS work?

A
  • at 10 weeks of pregnancy 90% of cell free DNA in blood is mom, 10% is from fetus
  • is due to apoptosis of placental cells
  • half life of 20 min, undetectable 2 hr after birth
  • use 150-250bp DNA and compare amount to a reference, healthy chromosome
  • if mom & baby have same amount as reference = healthy, if not = trisomy or aneuploidy
24
Q

How pick he reference DNA for NIPS?

A

-choose a reference chromosomes for only the specific chromosome you are scanning for, so for DS would be chrom 21 amount in the cell free DNA (cfDNA)

25
Q

positive predicted values (PPV) for NIPS

A
  • for DS is 93% in high risk populations; decreases w/ other syndromes
  • trisomy 18: 64%
  • trisomy 13: 44%
  • sec chrom. aneuploidy: 38%
  • lower PPV for avg risk pop
26
Q

Advantage of NIPS?

A
  • done early at 10 weeks of pregnancy
  • high sensitivity & specificity for DS
  • can do it when have multiples baby
  • insurances cover cost for high risk pop
27
Q

Disadvantage of NIPS?

A

-is not diagnostic testing
-if comes back + for DS; can’t determine if trisomy or translocation
can’t diagnose/screen for other things wrong
-obese moms more likely to get false negatives

28
Q

Incidental findings and NIPS?

A
  • can have incidental findings,

- can diagnose mama w/ cancer, sex chrom aneuploidy, trisomy

29
Q

ACOG Committee Opinion #640? (IMPORTANT)

A
  • is on NIPS states that:
    1) given limitations of NIPS & cost effectiveness, conventional screening is best for avg pop
    2) diagnostic testing recommended for any + result
    3) decisions to abort pregnancy shouldn’t be made on cfDNA results alone
    4) NIPS for micro deletions shouldn’t be performed on mamas w/ multiples
    5) a negative cfDNA test doesn’t ensure an unaffected pregnancy
30
Q

strengths of ultrasounds? Disadvantages?

A

strengths: detects 70% malformations

Dis-advatages: miss 30% malformations, is heavily dependent ton gestational age & position

31
Q

When is ideal time to do anatomy scan of baby?

A

20-22 weeks if baby is correct position

32
Q

Chorionic Villus Sampling?

A
  • completed 10.5- 13.9 weeks gestation
  • then do karyotype/array
  • risk 1/300 for complications
33
Q

How perform CVS (2 ways)

A
  • remove tissue from placenta
    1) transabdominally
    2) transcervically
  • dependent on physician preference & placenta location
34
Q

CVS disadvantages? (3)

A

1) risk of complciations)
bleeding, cramping, leakage of fluid, miscarriage are complications
2) doesn’t test for neural tube defects
3) can have mother cell contamination, so looking at mom chromosomes not baby

35
Q

placenta position and CVS

A
  • posterior: transcervically

- anterior: transabdominally

36
Q

Two ways mom can contaminant the CVS sample?

A

1) confined placental mosaism

2) maternal cell contamination

37
Q

confined placental mosaism in CVS

A

-sometimes sick cells can only be in placenta and baby is actually healthy

38
Q

maternal cell contamination in CVS

A
  • if find normal female chromosomes, could be mama & not baby
  • do extra studies to compare markers and make sure are seeing baby & not mom
39
Q

amniocentesis?

A
  • completed 16+ weeks gestation
  • karyotype/microarray & AF-AFP for open neural & abdominal wall defects
  • 1/400 risk of complication
40
Q

amniocentesis mechanism and benefits?

A
  • needle goes through abdomen into the amniotic sack, taking fluid from around baby
  • confinded placental mocaism & maternal cell contamination aren’t issues since remvoing fluid from directly around baby
41
Q

chromosomal microarray?

A
  • more common than karyotype

- detects copy number variation (CNV) deletions and duplications

42
Q

advantages for chromosomal microarray over other cytogenetics?

A

-finer resolution of breakpoints, defines genes involved & higher detection rates (can detect deletions & duplications <5MB, karyotype can’t)

43
Q

disadvantages for chromosomal microarray over other cytogenetics?

A

1) higher cost
2) doesn’t detect balanced rearrangements
3) can get unknown clinical significance (don’t know what result means)
4) finds non paternity/maternity

44
Q

how read a microarray?

A
  • the central line= normal/healthy

- anything above= duplication, below= deletion

45
Q

Single gene/ multi gene panel?

A
  • done on CVS/amnio
  • ordered when a fam history of known genetic condition, or if parents are found to be carriers via expanded screening
  • ultrasounds findings show possible genetic condition
46
Q

Advantage of single gene/ multi gene panel? Disadvantage?

A
  • advantage: less expensive then fetal exam

disadvantage: variants of uncertain significance

47
Q

fetal exam sequencing?

A
  • sequence all the protein coding genes

- mutations in these sequences more likely to have severe consequences

48
Q

advantages in fetal exam sequencing?

A
  • can be used in a structurally abnormal fetus when karyotype & array have shown normal results and help narrow down group of conditions baby could have
49
Q

disadvantages in fetal exam sequencing?

A

-variants of unknown significance, cost & who will pay,

50
Q

neural tube defects

A
  • group of malformations of the brain & spinal cord
  • includes anencephaly, spina bifida, encephalocele
  • 1/100 births
  • can be open or closed (open detected on maternal serum screening, closed doesn’t)
  • ultrasound detection ~ 90%

Block 1 Week 4 (7 decks)

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