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MGM (D) > Lecture 26 > Flashcards

Lecture 26 Flashcards

1
Q

What are the three most common chromosomal trisomies?

A

1) Down’s syndrome (trisomy 21)
2) Edward’s syndrome (trisomy 18)
3) Patao syndrome (trisomy 13)

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2
Q

What percentage of chromosomal abnormalities are present in miscarriages (SABs - Spontaneous Abortion), conceptuses (the embryo in the uterus, especially during the early stages of pregnancy) and liveborns respectively?

A

50%, 5% & 1%

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3
Q

Which is more harmful in general: A sex chromosome abnormality or an autosomal chromosome abnormality?

A

An autosomal chromosome abnormality

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4
Q

What is a requirement for a chromosome test to be done on a cell?

A

It must be nucleated (RBCs have no nucleus)

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5
Q

What are the most common cell types that undergo chromosomal testing?

A

Blood lymphocytes, amniocytes, fibroblasts and bone marrow cells

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6
Q

What is the most frequently used stain for chromosomal testing?

A

Giemsa stain

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7
Q

How are lymphocytes chromosomally tested?

A

1) A blood sample is added to culture media
2) Red blood cells are removed
3) T-cell division is stimulated
4) The cells are “frozen” in metaphase
5) The cells are lysed and dropped onto slides for analysis

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8
Q

What is Fluorescence in situ hybridization (FISH) used for?

A

To identify trisomies (extra chromosomes) or microscopic deletions in interphase or metaphase cells

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9
Q

What can be used to uncover complex chromosomal rearrangements?

A

Chromosomal paint - refers to the hybridization of fluorescently labeled, chromosome-specific, composite probe pools to cytological preparations; Usually used for cancer cells

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10
Q

What is Comparative genomic hybridization (CGH) used for?

A

To identify subtle chromosomal deletions and duplications

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11
Q

What is Comparative genomic hybridization (CGH)?

A

Comparative genomic hybridization is a molecular cytogenetic method for analyzing copy number variations relative to ploidy level in the DNA of a test sample compared to a reference sample, without the need for culturing cells (ratio between actual DNA and test DNA should always be 1:1 if they are normal)

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12
Q

What is the proper way to assign Cytogenetic nomenclature?

A

1) # of chromosomes or chromosomal units
2) Sex chromosome complement
3) Any structural or numeric variation not otherwise specified

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13
Q

What is SAB?

A

Spontaneous abortion or miscarriage

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14
Q

What is IUGR?

A

Intrauterine growth retardation (restriction)

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15
Q

What is MCA?

A

Multiple congenital anomalies

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16
Q

What is SS?

A

Short stature

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17
Q

What is ID?

A

Intellectual disabilities

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18
Q

What is LD?

A

Learning disabilities

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19
Q

What is ADHD/ADD?

A

Attention deficit hyperactivity disorder/Attention deficit disorder

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20
Q

What are signs of a prenatal chromosomal abnormality?

A

1) IUGR
2) MCA
3) hydrops/edema

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21
Q

What are signs of an infantile/childhood chromosomal abnormality?

A

1) MCA
2) unusual facial features
3) SS
4) ID
5) LD
6) ADHD

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22
Q

What are signs of an adulthood chromosomal abnormality?

A

1) LD
2) infertility
3) SABs
4) stillbirths

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23
Q

What is the anatomy or phenotype of a cytogenetic variation?

A

Fools Believe Genes are Disposable
F - Facial Features (dysmorphic)
B - Birth defects and physical variations
G - Growth retardation including head growth
D - Developmental problems

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24
Q

When does Trisomy 21 (Down’s Syndrome) become more common?

A

Non-disjunction that results in Down’s syndrome is associated with increasing maternal age.

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25
Q

Although most trisomy 21 cases are caused by non-disjunction, when is a robertsonian translocation most often seen?

A

In younger mothers with trisomic offspring; chromosome 21 is an acrocentric chromosome

26
Q

What are features of trisomy 21?

A

F - epicanthal folds, upslanting palpebrae

B - septal heart defects

27
Q

What percentage of trisomy 18 individuals are born?

A

5%

28
Q

Of all liveborns with trisomy 18, __% die in the first weeks of life, __% by two months and __% by one year of age

A

50%, 60%, & 95%

29
Q

What are key features of trisomy 18?

A

F - bird-like facies
B - rocker bottom feet
G - IUGR
Severe intellectual disabilities in survivors as well

30
Q

About ___% of Trisomy 13 individuals are due to a Robertsonian translocation

A

20%; chromosome 13 is an acrocentric chromosome

31
Q

About __% of trisomy 13 individuals die in the first month of life

A

50%

32
Q

What are key features of trisomy 13?

A

B - holoprosencephaly, oro-facial clefts, & extra finger/toes (polydactyly)
G - IUGR

33
Q

What is chromosomal mosaicism?

A

1) Mosaicism = more than one chromosomally distinct cell line in the same individual
2) Most often arise during early embryonic life with loss of a chromosome or unequal chromosomal segregation

34
Q

What is one of the most common cytogenetic deletions?

A

4p- (Wolf-Hirschhorn)

35
Q

What are key features of Wolf-Hirschhorn (4p-)?

A

F - helmet nose, arched eyebrows
B - oro-facial clefts
G - microcephaly (small head)

36
Q

What is a microdeletion or “contiguous gene” syndrome?

A

Results from small, sometimes submicroscopic deletions of genetic material

37
Q

What is a very common microdeletion?

A

22q11.2 deletion (DiGeorge syndrome, velocardiofacial syndrome)

38
Q

Why do individuals with microdeletions have similar physical features?

A

Loss of adjacent genes within the deletion region

39
Q

What are key features of 22q11.2 deletion (DiGeorge syndrome, velocardiofacial syndrome)?

A

F - long narrow face
B - conotruncal heart defects (major vessels), parathyroid gland function (hypocalcemia), T-cell defects (immunodeficiency), long tapered fingers
D - mild ID or LD

40
Q

When must a cytogenetic duplication always occur?

A

For every microdeletion there should be an equal and opposite microduplication

41
Q

What can be used to test for cytogenetic duplications?

A

Comparative genomic hybridization (CGH) to identify subtle chromosomal abnormalities

42
Q

What does an unbalanced translocation usually result in?

A

An unbalanced translocation usually results in a duplication (partial trisomy) and deletion (partial monosomy) of genetic material

43
Q

What does hemizygous mean?

A

Males only have a single X chromosome, so they are termed hemizygous

44
Q

Do females on average produce any more or less protein products for most genes because they have two X chromosomes?

A

No; One X chromosome is inactivated. However about 10 to 15% of genes on the X chromosome escape inactivation, especially on Xp

45
Q

Does the Y chromosome have any satellites?

A

No

46
Q

The Y chromosome replicates ____ than other acrocentric chromosomes

A

later

47
Q

What is a distinctive gene on the Y chromosome?

A

1) Testis determining factor that is responsible for male sexual differentiation
2) Also has genes for height, tooth size and hair growth in external ear

48
Q

Why are sex chromosome problems more common than autosomal chromosome problems?

A

Not as fatal

49
Q

If a mother does not have prenatal testing, will a sex chromosome aneuploidy for her baby be identified at birth?

A

Mostly no

50
Q

Are sex chromosome variations usually associated with intellectual disability?

A

No, but affected individuals can have mild developmental problems

51
Q

What is Turner syndrome?

A

Turner syndrome is a genetic condition in which a female does not have the usual pair of two X chromosomes

52
Q

What causes Turner syndrome?

A

Most often results when a normal egg is fertilized by a sperm without a sex chromosome

53
Q

What can Turner Syndrome lead to?

A

Ovarian failure and short stature

54
Q

What are key features of Turner Syndrome?

A

F - webbed neck
B - coarctation of the aorta
G - SS in childhood
D - LD and/or visual-spatial perceptual problems, infertility due to ovarian failure

55
Q

What does Triple X syndrome result in?

A

1) No physical feature at birth (no recognized phenotype)
2) Mild LD and increased risk for psychiatric disorders
3) Usually normal fertility but increased risk for premature ovarian failure

56
Q

What does Klinefelter syndrome (47 XXY) result in?

A

1) Increased risk for mild LD
2) Behavioral and socialization difficulties
3) Breast enlargement (gynecomastia), small testes and infertility

57
Q

What does (47 XYY) result in?

A

1) Mild LD, ADHD & behavioral problems
2) Tall stature may be seen
3) Normal fertility

58
Q

What can happen during an X chromosome translocation with an autosome?

A

The normal X chromosome may appear to be preferentially inactivated. This most likely results from “selection” or non-viability of cells with the translocated or derivative X inactivated. It can result in expression of an X-linked recessive condition in a female

59
Q

How can a female express an X-linked recessive disorder?

A

1) By inheriting two copies of the recessive gene - one from each parent (a double dose)
2) X autosome translocations with cellular “selection” or non-viability
3) Turner syndrome
4) Manifesting heterozygotes may also result from unfavorable or skewed X-inactivation for single gene disorders such as Duchenne muscular dystrophy or hemophilia

60
Q

If a child has multiple congenital anomalies, poor growth, and ID, what chromosomes are you concerned about?

A

Autosomal chromsomes

61
Q

If an individual has mild learning problems, social difficulties and/or fertility problems, what chromosomes are you concerned about?

A

Sex chromsomes

MGM (D) (71 decks)

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