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Block I: Reproduction & Sexuality > Genetics: Prenatal Diagnosis > Flashcards

Genetics: Prenatal Diagnosis Flashcards

1
Q

8 indications for referral to prenatal diagnosis

A
  • Advanced maternal age (being phased out)
  • Abnormal (positive) results of maternal serum screening
  • Abnormal findings on ultrasound
  • Previous child with a chromosome abnormality
  • Parental chromosome abnormality
  • Family history of other genetic disorder or malformation
  • Teratogen exposure
  • Infertility
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2
Q

Karyotope of normal female

A

46,XX

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3
Q

Karyotype of normal male

A

46,XY

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4
Q

Trisomy 21 Karyotype (Down Syndrome)

A

47,XX+21

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5
Q

5 characteristics of Trisomy 21 (Down sydrome)

A
  • Hypotonia
  • Characteristic dysmorphic features
  • Congenital heart defects (40-50%)
  • Hirschprung, duodenal atresia, others
  • Intellectual disability
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6
Q

Trisomy 18 Karyotype

A

47,XY,+18

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7
Q

5 characteristics of Trisomy 18

A
  • Overlapping fingers
  • Rockerbottom feet
  • Growth & developmental retardation (severe)
  • Congenital heart defect (~90%)
  • Most do not live long (central apnea), but rare ones live into early childhood
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8
Q

Karyotype of Trisomy 13

A

47,XY,+13

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9
Q

7 characteristics of Trisomy 13

A
  • Holoprosencephaly (60-70%) (failure of brain cleavage –> one lobe)
  • Clenched hands and polydactyly (60-70%)
  • Cutis aplasia (absence of development of skin)
  • Cleft lip and palate (60-70%)
  • Cardiac malformations (80%)
  • Severe/profound intellectual disability
  • Shortened lifespan as in trisomy 18
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10
Q

Klinefelter Syndrome Karyotype

A

47,XXY

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11
Q

Karyotype of Turner Syndrome

A

45,X

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12
Q

5 characteristics of Klinefelter syndrome

A
  • Poor beard growth
  • Breast development
  • Under-developed testes
  • Tall stature
  • Infertility
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13
Q

7 characteristics of Turner Syndrome

A
  • Characteristics facial features
  • Web of skin
  • Constriction of aorta
  • Poor breast development
  • Under-developed ovaries
  • Short stature
  • Infertility
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14
Q

One risk factor for trisomies

A

Advanced maternal age (NOTE: Turner syndrome is NOT associated with this)

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15
Q

Explain the frequency of chromosome abnormalities linked to maternal age throughout gestation

A

Decreased frequency due to demise (miscarriage)

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16
Q

Threshold age where it is appropriate to offer amniocentesis (benefit outweighs risk of procedure)

A

35

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17
Q

3 screening programs designed to provide a woman with a more precise risk that that based upon maternal age alone and that she is carrying a fetus with one or more specific genetic conditions

A
  • Down Syndrome (trisomy 21)
  • Trisomy 18
  • Spina bifida
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18
Q

3 parameters that are important in a screening program

A
  • Sensitivity (detection rate)
  • Positive predictive value
  • False positive rate
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19
Q

Goal of a screening program

A

Maximize sensitivity and minimize FP

20
Q

Define sensitivity of a genetic screening test

A

% affected fetuses that have positive result

21
Q

Define positive predictive value of a genetic screening test

A

% screen positive cases that are truly affected

22
Q

Define false positive rate of genetic screening test

A

% screen positive cases that are unaffected

23
Q

Sensitivity of advanced maternal age screening program

A

~30% of affected pregnancies detected

NOTE: Reason = most women have their pregnancies under 35 so less total over 35

24
Q

3 fetoplacental products used in 2nd trimester maternal serum screening

A
  • Alphafetoprotein (AFP)
  • Unconjugated estriol (uE3)
  • Human chorionic gonadotropin (hCG)

NOTE: Median concentration in Down syndrome fetuses sufficiently different to predict increased risk, but does not tell you about the actual health of the fetus

25
Q

Fetal condition associated with increased AFP

A

Open neural tube defects (i.e. spina bifida)

NOTE: Nowadays detectable by US very well instead of msAFP

26
Q

3 aspects of the 1st trimester screening program

A
  • Muchal translucency thickness (NT) by ultrasound
  • Serum markers
    • Pregnancy-associated plasma protein A (PAPP-A)
    • B-hCG
27
Q

Define nuchal translucency

A

Normal to have fluid under skin, but abnormal to have a large amount under the skin, around the neck

28
Q

4 Risks associated with finding increase nuchal translucency

A
  • Associated with congenital heart defects and other abnormalities
  • 20-30% have adverse pregnancy outcome
    • Fetal demise
    • Preterm delivery
    • Low birth weight
29
Q

1st and 2nd trimester integrated screening programs

A
  • 1st tri = NT, PAPP-A (hold results)
  • 2nd tri = various combinations of AFP, uE3, hCG, inhibin-A
30
Q

New non-invasive prenatal testing program (2010’s)

A

Circulating cell-free fetal DNA (starting from 10 weeks gestation)

31
Q

2 points of screening

A
  • Identify younger women who are at increased risk, offer invasive test
  • Identify older women who are at decreased risk, avoid invasive test
32
Q

2 current guidelines for prenatal screening

A
  • Must do screening first, no matter what age
  • Only offer prenatal diagnosis if results are positive
33
Q

4 major malformations that may be found on ultrasound

A
  • Cardiac malformations
  • Cystic hygroma (usually Turner Syndrome)
  • Omphalocele
  • Neural tube defects
34
Q

6 markers (“soft signs”) for aneuploidy

A
  • Nuchal fold
  • Echogenic bowel
  • Short femur
  • Intracardiac echogenic focus
  • “Absent” nasal bone
  • 5th finger cilnodactyly
35
Q

3 reasons why risk of recurrence for is slightly increased by ~1% to have a second child with a chromosome abnormailty

A
  • Parental mosaicism
  • Parental predisposition to nondisjunction
  • Chance
36
Q

2 risks of unbalanced offspring

A
  • Miscarriage
  • Abnormal liveborn (i.e. malformations, growth and/or developmental delay)
37
Q

Define teratogen

A

Agent that can disturb the development of an embryo or fetus.

38
Q

5 examples of teratogens

A
  • Radiation
  • Maternal infections
  • Maternal disease (poorly controlled diabetes, phenylketouria)
  • Chemicals
  • Drugs
39
Q

2 prenatal diagnosis techniques (to acquire sample)

A
  • Chorionic villus sampling (CVS)
  • Amniocentesis
40
Q

When can CVS be done?

A

11 weeks

41
Q

2 technical issues of CVS

A
  • Mosaicism
  • Maternal cell contamination in ~4% of cases
42
Q

When can amniocentesis be done?

A

14 - 17 weeks or later

43
Q

2 genetic tests to use on samples for prenatal diagnosis

A
  • Cytogenic studies
  • DNA analysis
44
Q

Information provided by cytogenic studies

A

Karyotype

45
Q

Information provided by DNA analysis of prenatal diagnosis sample

A
  • Direct mutation detection, sequencing, etc. for single gene disorders
  • aCGH

Block I: Reproduction & Sexuality (23 decks)

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