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Genetics 3 > Prenatal Diagnosis > Flashcards

Prenatal Diagnosis Flashcards

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1
Q

What are the non-invasive prenatal diagnostics?

A

Ultrasound, AFP, Quad Screen

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2
Q

What are the invasive prenatal diagnostics?

A

Amniocentesis, chorionic villus sampling, Percutaneous umbilical blood sampling (PUBS)

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3
Q

What is the goal of maternal serum screening

A

identify patients at increased risk of fetal disorder to then offer diagnostics. Maternal serum screening is non-diagnostic.

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4
Q

When do Neural tube defects occur?

A

3rd to 4th week of fetal embryonic development

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5
Q

What is the incidence of ONTDs?

A

1-2/1,000 live births

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6
Q

What causes ONTDs?

A

15% are chromosomal abnormalities, single gene defects, teratogens. 85% are multifactiorial. Folic acid decreases risk by 50-75%.

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7
Q

What is the recommended dose of Folic acid for pregnant women and those with prior affected pregnancies?

A

0.4mg/day for all women, 4mg/day for mom’s with prior affected pregnancy

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8
Q

What can cause false positives for AFP?

A

Theres an area of overlap for AFP that can be normal, trisomy 21, or NTD. Normally trisomy 21 has low levels of AFP and NTD has high levels. This causes false positives.

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9
Q

What is the quad screen?

A
  1. Pregnancy Associated Plasma Protein A (PAPP-A)
  2. Alpha fetoprotein
  3. HCG - free beta human chorionic gonadotropin
  4. uE3 - unconjugated estradiol
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10
Q

What is maternal serum screening for Down’s syndrome?

A

Triple: low AFP + high HCG + low uE3 + Maternal age
Detection rate is 60-65%, FPR 5%
Quad: PAPP-A will be low

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11
Q

What is maternal serum screening for Trisomy 18?

A

All serum biochemical markers are low. DR = 60-80%. FPR = 0.2%

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12
Q

What is nuchal translucency?

A

thickened translucency correlates to increased risk of trisomies. NT measurement cutoff varied from greater than 2.0 mm to 10.0 mm.

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13
Q

What is NT + Maternal Serum Screening?

A

Nuchal translucency measurement (10 weeks, 4 days to 13 weeks, 6 days) + blood spot card to measure HCG and PAPP-A. Sensitivity increases.

91% DR for Downs, FPR still 5%
97% for Trisomy 18, FPR still .4%

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14
Q

What about ultrasound screening for chromosomal abnormalities?

A

a normal ultrasound does not exclude the possibility of chromosomal abnormalities

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15
Q

How good is ultrasound for detection of ONTDs?

A

Sensitivity is 80-95%. Look for Lemon sign and banana sign. Hydrocephalus occurs in most.

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16
Q

What is the lemon sign?

A

On ultrasound, frontal bones of skull are flattened instead of rounded, looking like a lemon.

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17
Q

What are the ultrasound findings for down syndrome?

A

nuchal thickening, echogenic bowel, shortened humerus and femur, absent nasal bone, duodenal atresia “double bubble” on US

18
Q

What are the ultrasound findings for Trisomy 13?

A 
Holoprosencephaly: failure of hemispheres to develop
cleft lip/palate
polydactly 
Omphalocele
NTD
19
Q

What are the ultrasound findings for Turner Syndrome?

A

Cystic hygroma - retention of fluid in lymphatics
Congenital heart defect (20%)
Horseshoe kidney + renal anomalies (60%)
non-immune hydrops - accumulaton of body fluid in body cavities

20
Q

What is the primary advantage and disadvantage of ultrasound?

A

Advantage - noninvasive, doesn’t disturb fetal environment

Disadvantage - cannot pick up all birth defects

21
Q

What is an amniocentesis?

A

removing a sample of amniotic fluid with sloughed off fetal cells, performed at 15-16 weeks, earlier its done (11 weeks) - greater the risk to the fetus

22
Q

What is AFP?

A

fetal glycoprotein produced mainly in liver and secreted into fetal circulation. Also enters maternal blood stream and assayed in maternal serum AFP

23
Q

What are the risks of amniocentesis?

A

1/200 - 1/300 (0.5 - 0.3%) risk of miscarriage, most dangerous at 10-14 weeks

24
Q

What is chorionic villus sampling?

A

remove small amount of chorionic tissue (pre-placental) at 11-12 weeks, cannot assay AFP.

25
Q

What is the risk of chorionic sampling

A

0.5 - 1% chance of misscarriage, limb abnormalities if before 10 weeks. Contraindicated with STD, unusual anatomy

26
Q

PUBS - percutaneous umbilical blood sampling?

A

use ultrasound guidance to take sample from umbilical cord. Use when amniocentosis gives ambiguous results.

27
Q

What is the risk of PUBS

A

2-3% miscarriage, risk of hemorrhaging, normally performed at 19-20 weeks

28
Q

What is cffDNA?

A

Cell Free Fetal DNA is non-invasive way to test placental cells in maternal circulation (2-6%). Detectable as early as 4 weeks.

29
Q

How do you find cffDNA is maternal blood?

A

Fetal DNA will have different methylation patterns and different sequences than mom.

30
Q

What are the clinical uses of cffDNA

A

Fetal sex determination, x-linked recessive disorders, Rh disease, aneuploidy (T13,21,18), monogenic disorders

31
Q

What is cffDNA most useful for>

A

Trisomy 21, positive cffDNA screenings require invasive follow up screenings

32
Q

What are malformations?

A

instrinsic abnormalities in genetic programming (extra fingers)

33
Q

What are deformations?

A

Usually resolve, extrinsic factors physically impinging on developing fetus. Example is leaking amniotic fluid

34
Q

What are disruptions?

A

destruction of irreplaceable fetal tissue. Can results from vascular insufficiency, trauma, or teratogen. Example is amniotic bands

35
Q

What are the two mechanisms of fate specification?

A
  1. cell to cell signaling - ligand binds receptor, signaling ascade –> cell fate specification
  2. asymmetric segregation of determinants (determinants specify cell fate)
36
Q

What is thalidomide?

A

teratogen, prescribed to women to treat emesis and caused limb defects, believed that it inserts itself in DNA and interferes with expression of genes.

37
Q

How does oral retinoid cause birth defects?

A

isotretinoin mimics retinoic acid and disrupts normal development, causing hydrocephaly, microcephaly, MR, ear/eye abnormalities, cleft/lip palate

38
Q

What are the four characteristics required for a diagnosis of fetal alcohol syndrome?

A
  1. Pre or postnatal height or weight below 10th percentile
  2. 3 facial features: smooth philtrum, thin vermillion, small palpebral fissures
  3. CNS damage - structural (microcephaly), neurological, or functional (MR)
  4. Prenatal exposure to alcohol
39
Q

What birth defects does cocaine cause?

A

premature birth, non-doudenal intestinal atresia, limb reduction

40
Q

What are the birth defects caused by insulin-dependent diabetes?

A

2-30x incidence of birth defects and miscarriage
excessive birth weight
neonatal hypoglycemia
brain, heart, intestine, kidney, and lower spinal defects

41
Q

What disorders have high recurrence risk and which ones have low?

A

High - x-linked recessive or autosomal recessive

Low - uniparental disomy, new mutation, teratogen exposure (just remove teratogen)

Genetics 3 (4 decks)

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