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Embro & Repro - GC > Fetal Aneuploidy > Flashcards

Fetal Aneuploidy Flashcards

1
Q

What percentage of trisomy 21 aneuploidies are maternal in origin?
What percentage of those errors occur in meiosis 1 and in meiosis 2?

A

Maternal = 93%
Meiosis 1 = 3/4
Meiosos 2 = 1/4

It is estimated that 24% of these aneuploidies will survive to term.

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2
Q

Which aneuploidy is attributed about evenly in parental origin?

A

XXY
XXY is paternal in origin 45% of the time and maternal 55%. These aneuploidies have a 53% chance to survive to term.

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3
Q

Most aneuploidies are attributed to which parental origin?

A

Maternal. The only aneuploidy more commonly of paternal origin is XO. Which is attributed to paternal origin, about 80% of the time.

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4
Q

What is the most common chromosomal abnormality among liveborn individuals?

A

Trisomy 21

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5
Q

What are the acrocentric chromosomes?

A

13, 14, 15, 21, 22

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6
Q

How many chromosome does a Robertsonian Translocation carrier have?

A

45 because 2 chromosomes are stuck together

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7
Q

What is nondisjunction?

A

Nondisjunction: failure of chromatids (during mitosis or meiosis II) or chromosomes (during meiosis I) to separate at anaphase

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8
Q

Nondisjunction in meiosis results in….

A
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9
Q

What is anaphase lag?

A

failure of a chromatid or chromosome to attach to the spindle and segregate into a daughter cell

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10
Q

What is the difference in result of anaphase lag vs nondisjunction in mitosis?

A

anaphase: 1 daughter cell with normal chromomsal content & 1 daughter cell with monosomy for one chromosome
nondisjunction: One daughter cell with trisomy for the chromosome which nondisjoined
& One daughter cell with monosomy for the same chromosome

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11
Q

What is the leading genetic cause of intellectual disability?

A

aneuploidy

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12
Q

What percentage of live births are aneuploid?

A

0.3%

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13
Q

What percentage of oocytes are aneuploid? What percentage of sperm are aneuploid?

A

oocytes = 20 - 25%
sperms = 1 -2%

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14
Q

Do most aneuploidies happen in meiosis I or meiosis II?

A

meiosis I

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15
Q

What is the parental orgin of trisomy 16?
How many survive to term?

A

100% maternal
0% survive to term

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16
Q

What percentage of XXX aneuploidy pregnancies survive to term?

A

95%

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17
Q

Of maternal meiosis errors how many occur in meiosis I and how many occur in meiosis II?

A

¾ occur in meiosis I
¼ occur in meiosis II

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18
Q

How do the rates of aneuoploidies of live births compare to rates of aneuploidies at CSV or amnio?

A

Rates at CVS & amnio are higher (assumingly b/c pregnancies do not always make it to term with aneuploidies)

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19
Q

What percentage of patients with Down syndrome have trisomy 21?

A

95%

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20
Q

What is the most common translocation for those with Down syndrome?

A

14;21 Robertsonian translocation

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21
Q

Most cases of 21;21 Translocation Down syndrome are…

A

de novo

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22
Q

Down syndrome recurrence risk

A

 Parents of a child with trisomy 21: 1% risk for any aneuploidy in a future pregnancy
 Carrier of a 14;21 translocation: 5-15%
 Carrier of a 21;22 translocation: 6%
 Carrier of a 21;21 translocation: 100%

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23
Q

What is the genotype of trisomy 13

A
  • 80% of affected individuals have trisomy 13
  • 20% of affected individuals have a trisomy of chromosome 13 due to a
    13;14 translocation
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24
Q

What percentage of fetuses with trisomy 13 will show findings on ultrasound?

A

90%

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25
Q

Common features of trisomy 13

A

cleft lip &/or cleft palate
cardiac issues
lots of others

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26
Q

Survival for trisomy 13

A

median survival: 2.5 days
6-month survival: 5%

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27
Q

What is another name for trisomy 13?

A

Patau syndrome

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28
Q

What is another name for trisomy 18?

A

Edwards Syndrome

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29
Q

What is the developmental capacity for someone with trisomy 13 or trisomy 18?

A

For both trisomy 18 and trisomy 13, the developmental age of a child who
lives longer than one year is expected to be in the range of a 6-9 month old
- May sit independently, but not expected to walk
- Will need daily assistance with basic living tasks (e.g. feeding, toileting, dressing, etc.)

30
Q

Clinical features of trisomy 18

A
  • intellectual disability
  • hypotonia –> hypertonia
  • rocker bottom feet
  • and many more
31
Q

What is the most common trisomy in spontaneous abortions?

A

trisomy 16

32
Q

Autosomal monosomies are generally considered to be…

A

nonviable

33
Q

What is triploidy?

A

3 sets of chromosomes
(69,XXY; 69XXX; 69XYY)

34
Q

Are most triploidies diandric (2 paternal sets) or digynic (2 maternal sets)?

triploidy = 3 sets of chromosomes instead of 2

dric = dick
gyn = gyne

A

85% are diandric (2 paternal sets)
15% are digynic (2 maternal sets)

b/c we always have too many men around causing problems

35
Q

What is a characteristic feature of triploidies?

A

3,4 syndactyly
(start counting from the thumb)

36
Q

What are the mechanisms by which triploidies can occur?

A
  • a haploid egg fertilized by 2 sperm
  • a haploid egg fertilized by a diploid sperm
  • a diploid egg fertilized by a haploid sperm
37
Q

What are the features and expected outcomes for a diandric triploidy fetus?

diandric = 2 paternal sets of chromosomes

A

Well-grown fetus with proportionate or slightly small head, large placenta. Usually do not survive to term

compare to digynic

38
Q

What are the features and expected outcomes for a digynic triploidy fetus?

digynic = 2 maternal sets of chromosomes

A

Growth-restricted fetus with macrocephaly and small, fibrotic placenta. Can survive to term and live ~1 year.

compare to diandric

39
Q

Aneuploid mosaics can start out as trisomic conceptions and lose one copy of the trisomic chromosome (trisomy rescue). What are these pregnancies at risk of occuring?

A

uniparental disomy

note: compare to gaining a chromosome thorugh mitotic nondisjunction which has no risk of uniparental disomy

40
Q

Diploid/Triploid Mosaicism - compared to true triploidy what are the outcomes like?

A
  • Less severely affected with survival >10 years reported
  • Growth restriction, asymmetric growth, syndactyly, physical and intellectual
    disability
  • mechanism is unknown
41
Q

How does a complete molar pregnancy happen?

A
  1. An egg with no genetic infomraiton is fertilized by a sperm which replicates itself (endoreduplicates) to reach 46 chromosomes (diandric diploidy)
  2. An egg with no genetic information is fertilized by 2 sperms.
    - these 2 scenarios cover 80% of cases, so I’m not sure how the rest of the cases occur
42
Q

What major risk do complete molar pregnancies pose to the woman?

A

15-20% risk of degenerating into a
choriocarcinoma

chorio b/c derived from chorionic villi

43
Q

What are the fluid filled cysts in the placenta of a molar pregnancy derived from?

A

chorionc villi

44
Q

What are the features of a partial molar pregnancy?

A
  • a fetus is present in the early stages
  • usually diandric triploidy or tetraploidy

diandric = paternal (dick)

45
Q

What is tetraploidy?

A

Four sets of chromosomes
(92,XXXX or 92,XXYY)

46
Q

What is the probable origin of tetraploidy?

A

duplication of chromosomes without cell division in the zygote

47
Q

What is another name for Monosomy X?

A

Turner Syndrome

48
Q

Incidence and Features of Monosomy X/ Turner Syndrome

A
  • 1 in 2,000 to 1 in 5,000 female livebirths
  • Prenatally associated with cystic hygroma, severe lymphedema, hydrops, and high
    risk of fetal demise
  • In the newborn period; presence of lymphedema, webbed neck, congenital heart
    disease (often coarctation of the aorta), typical linear growth until age 2-3
  • In childhood; short stature, low posterior hairline, cubitus valgus, short metacarpals,
    disproportionately short legs, broad chest, prominent ears, pigmented nevi, scoliosis,
    micrognathia
  • In adolescence; delayed puberty
  • In adults; infertility
  • Other features; increased risk for specific learning disabilities involving spatial
    perception. Renal abnormalities (e.g., horsehoe kidney) are common
  • Tend to struggle with math and spatial awareness

I’m having trouble pairing this one down. Please change if you know how.

49
Q

What is one reason why it is so important to karyotype Monosomy X patients?

A

They may have Variant Monosomy X and the risk of gonadoblastoma is 15-20% in patients with 45,X/46,XY mosaicism and female or ambiguous genitalia

50
Q

What is a common feature of those with sex chromosome abnormalities?

A

intellectual disability

51
Q

Does having chromosomal aneuploidy 47,XYY increase the risk for violence?

A

No.

52
Q

What is the trend of spontaneous abortions related to chromosome abnormality?

A

The earlier in pregnancy the spontaneous abortion, the more likely that its cause was related to a spontaneous abortion.

53
Q

Are there different risks for those that inherited balanced translocations vs those that had de novo balanced translocations?

A

Yes
- inherited = normal phenotype
- de novo = ID, congenital anomalies

54
Q

What is the most common Robertsonian Translocation?

A

der(13;14)(q10;q10)
Note: “der” refers to a chromosome “derived” from a translocation, or trading of pieces of chromosome between members of different homologous pairs

55
Q

What are the reproductive risks for someone with a Robertsonian Translocation?

A

Carriers have an increased risk for
infertility, unbalanced offspring,
offspring with uniparental disomy

56
Q

ACMG recommends that UPD testing be considered when a carrier fetus is
identified with a Robertsonian involving chromosomes 14 or 15 and patients
with abnormal phenotypes and a balanced Robertsonian involving chromosomes 14 or 15. What is one reason for this recommendation?

A

chromosomes 14 & 15 involve imprinting so it is important to know if UPD

57
Q

What are Recriprocal Translocations?

A

Exchange of genetic material between non-homologous chromosomes or between homologous chromosomes at non-homologous sites

58
Q

Are most balanced reciprocal translocations inherited?

A

Yes, 70% are.

59
Q

How are balanced reciprocal translocation carriers effected by these variants?

A

Although balanced carriers are usually phenotypically normal, they have a significant risk for infertility, miscarriage, and birth of children with abnormal phenotypes

60
Q

Why is determining risk for reciprocal translocation carriers so difficult?

A

Most reciprocal translocations are “private” (i.e. only found in one family)

61
Q

Does alternate segregation result in normal or aneuploid gametes?

A

all normal gametes

compare to adjacent

62
Q

Does adjacent segregation result in normal or aneuploid gametes?

A

Aneuploid gametes

dcompare to alternate

63
Q

Describe what an inversion is.

A

As the name would suggest, an inversion happens when two breaks in a single chromosome occur and the segment between the breaks rotates180 degrees and is reinserted in the same spot.

64
Q

What is the difference between pericentric inversions and paracentric inversions?

A

Inversions can be pericentric (include the centromere) or paracentric (no centromere involvement)

65
Q

Do inversions always have adverse effects? What adverse effects can they have?

A

While some inversions segregate through families without adverse effects, other inversions can be associated with an increased risk for miscarriage and abnormal offspring

66
Q

Why are more distal breakpoints more concerning than those close to the centromere in pericentric inversions?

A

The more distal the breakpoints, the
larger the inversion, and the higher the
risk for abnormal children
- The farther apart the breakpoints, the
more likely that crossovers will occur
between them and large inversions
have small distal segments which,
when duplicated or deleted, have a
higher probably of producing
abnormal offspring that survive
postnatally
Small inversions (breakpoints close to the
centromere) are rarely associated with
reproductive problems

67
Q

Why are paracentric inversions lethal and rarely seen in liveborn children?

A
  • Acentric fragment does not have
    a centromere and cannot be
    pulled to the pole during meiosis
  • Dicentric fragments are unstable,
    pulled to opposite poles and
    break at a random position, with
    resultant production of two
    duplication/deletion products
68
Q

How does Ring X Syndrome present?

A

Turner syndrome phenotype but with intellectual disability

69
Q

What are Marker Chromosomes?
What disability are they associated with?
What ar they derived from?

A
  • extra structurally abnormal chromosomes whose origin are not apparent by routine cytogenetic analysis
  • associated with intellectual disability
  • 80% are derived from acrocentrics; 40% from
    chromosome 15 alone
70
Q

Are pericentric or paracentric inversions more concerning for the phenotype of offspring?

A

Risk in cases of inversions depends on the location of the inversion with respect to the centromere and on the size of the inverted segment. For inversions that do not involve the centromere (paracentric inversions), there is a very low risk for an abnormal phenotype in the next generation. But, for inversions that do involve the centromere (pericentric inversions), the risk for birth defects in offspring may be significant and increases with the size of the inverted segment.

Embro & Repro - GC (7 decks)

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