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MCS > Day 4, Lecture 2: Genetics V: Human Chromosome Abnormalities > Flashcards

Day 4, Lecture 2: Genetics V: Human Chromosome Abnormalities Flashcards

1
Q

Clinical Cytogenetics

A
  • Study of the relationship of chromosomal alterations and genetic diseases in human beings
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2
Q

Chromosomal abnormalities cause

A
  • Pregnancy loss
  • Congenital malformations
  • Intellectual disabilities (Mental Retardation)
  • Play a role in the pathogenesis of malignancy
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3
Q

How common are chromosome abnormalities

A
  • about 1% of live births
  • about 50% of first trimester miscarriages
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4
Q

Classification of cytogenetic mutations

A
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5
Q

Numerical Chromosome Abnormalities

A
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6
Q

What is the most common chromosome abnormality seen in live births?

A
  • Trisomy 21
  • Incidence 1 out of every 691 live births
  • Can happen to women of all ages, races and economic levels
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7
Q

Causes of Trisomy 21

A
  • Caused by having 3 compies of chromsome 21
    • 95% is nonfamilial Trisomy 21
    • 3-4% is unbalanced translation
      • only 1% are familial unbalanced translocation
    • 1-2% is mosaicism with two cell lines- normal and trisomy 21
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8
Q

Common Aneuploidy Conditions

A
  • Autosomes
    • Trisomy 21
    • Trisomy 18
    • Trisomy 13
  • Sex Chromosomes
    • Monosomy X
    • Klinefelter Syndrome
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9
Q

Clinical Features of Trisomy 21

A
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10
Q

What is Mosaicism?

A
  • The situation in which not all cells in an organism possess the same genotype. Mosaicism usually occurs as the result of postconceptional (acquired) changes.
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11
Q

Trisomy 18 (Edwards Syndrome)

A
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12
Q

Trisomy 13 (Patau Syndrome)

A
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13
Q

Monosmy X (Turner Syndrome)

A
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14
Q

Klinefelter Syndrome (47, XXY)

A
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15
Q

Do Chromosome aneuploidy conditions usually run in families?

A
  • No, it is a sporadic event
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16
Q

Structural Abnormailities

A
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17
Q

What is an Isochromosome?

A

One arm is duplicated forming two arms with a shared centromere

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18
Q

Chromosomal Translocations

A
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19
Q
A
20
Q
A
21
Q

Microdeletion Syndromes bridge the gap between

A
  • Single gene and chromosomal syndromes
    • The deletion of a megabase or so is too small to be seen under the microscope, however, it may involve a dozen or more genes
    • FISH analysis and chromosome microarray are revealing increasing numbers of such submicroscopic chromosomal abnormalities
22
Q

Molecular pathology puts deletions/duplications into what three categories

A
23
Q

microdeletion syndromes, contiguous gene syndromes, and segmental aneuploidy are now generally referred to as

A
  • Genome disorders
    • (note: Genome disorders have a complex phenotype (frequently includes mental retardation, developmental delay, and behavioral problems) due to alteration of gene dosage)
      • Haploinsufficiency
        • Deletion (majority of genome disorders)
        • Terminal deletion (telomeric)
        • Imprinting or UPD
      • Overexpression
        • Duplication (minority of genome disorders)
24
Q

Mechanism of genome disorders

A
  • Usually less than 5Mb is involved in the deletion or duplication that leads to a genome disorder
  • Areas of high recombination are often flanked by unique low copy repeats
  • Due to the low copy repeats, the chromatids misalign during recombination in meiosis
  • This misalignment leads to non-homologous recombination and unequal crossing-over
25
Q

Can a child inherit a microdeletion syndrome from a parent?

A

Yes

26
Q

Williams Syndrome

A
27
Q

Langer-Giedon Syndrome

A
28
Q

DiGeorge Syndrome

A
29
Q

Duplication 22q syndrome

A
30
Q

Prader-Willi Syndrome

A
31
Q

Angelman Syndrome

A
32
Q

Genetics of Prader-Willi/Angelman Sydrome

A
33
Q

1p36 Deletion Syndrome

A
34
Q

Cri-du-Chat Syndrome

A
35
Q

Wolf-Hirschorn Syndrome

A
36
Q

Smith-Magenis Syndrome

A
37
Q

Chromosome Analysis

A
38
Q

Karyotype

A
39
Q

Metacentric

A
  • Centromere is central with arms being almost equal length
40
Q

Submetacentric

A

Off-centered centromere with arms being different lengths

41
Q

Acrocentric

A

Centromere is near one end

42
Q

Fluorescence in situ hybridization (FISH)

A
  • Uses fluorescent probes that bind to only those parts of the chromosome indicated for study
  • Used to detect microdeletion syndrome, aneuploidy, unknown chromosome material seen on karyotype
43
Q

explain how FISH is able to show a deletion syndrome

A
  • A chromosome reporter probe is able to show which chromosome you are looking for a deletion at
  • A critical region probe will attach if the genes are there and will not attach if they have been deleted (example in the picture)
44
Q

Chromosome Microarray analysis (aka Comparative genome hybridization (CGH))

A
  • Genome-wide screening
  • used to measure the differences between two different DNA samples (control and test) in copy number, or dosage, of a particular DNA segment
  • Limitations:
    • Cannot detect balanced rearrangments
    • Cannot provide the physical location of copy-number variants of unkown clinical significance
    • Cannot detect low levels of mosaicism
45
Q

Specimen Types for Chromosome Analysis

A
  • White blood cells in peripheral blood
    • preferred specimen type
  • Fibroblasts from skin biopsy
  • Solid tumor biopsy
  • Bone marrow
  • Fetal cell derived by
    • amniocytes from amniotic fluid
      • Collected via a procedure called amniocentesis
    • Chorionic villus cells
      • Collected via a procedure called chorionic villus sampling
    • Fetal blood
      • Collected via a procedure periumbilical blood sampling
    • Products of Conception
46
Q

Abbreviations used to describe chromosome and their abnormalities

A

MCS (40 decks)

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