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MICN201 2025 Genetics > Analysis of Chromosomal Disorders in the Clinic - 1 > Flashcards

Analysis of Chromosomal Disorders in the Clinic - 1 Flashcards

(59 cards)

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1
Q

What are the aims of the analysis of chromosomal disorders?

A
  • Describe common chromosomal abnormalities and how they arise
  • Understand the breadth of indications for chromosomal analysis
  • Understand the diagnostic techniques used to analyse chromosomal structure
  • Be familiar with the interpretation of a karyotype
  • Describe the features of the sex chromosomes and the clinical consequences of numerical abnormalities (e.g Turner/Klinefelter)
  • Describe features and causes of the common aneuploidies (e.g. Trisomy 21)
  • Describe the origin and outcomes of balanced reciprocal and Robertsonian translocations, and other structural alterations (e.g. duplications, deletions, insertions) of chromosomes
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2
Q

What is the karyotype nomenclature for a balanced translocation between chromosomes 5 and 10?

A

46,XY,t(5;10)(p13;q25)

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3
Q

What is the karyotype nomenclature for Down syndrome?

A

47,XY,+21

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4
Q

What is the incidence of Turner syndrome?

A

1:3000

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5
Q

What are the common features of Turner syndrome?

A
  • Neonatal oedema/webbed neck
  • Coarctation of the aorta
  • Linear growth delay
  • Primary amenorrhoea
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6
Q

What is the karyotype for Klinefelter syndrome?

A

47,XXY

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7
Q

What are the clinical indications for chromosomal analysis?

A
  • Abnormality of growth or development (a “syndrome”)
  • Intellectual disability
  • Recurrent miscarriage
  • Investigation of cancers (e.g. leukaemia)
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8
Q

What is the main technique used to analyse chromosomal balance?

A

Chromosomal microarray

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9
Q

True or False: Chromosomal variants are common, but not all cause disease.

A

True

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10
Q

What is the appropriate gene dosage for autosomal genes?

A

Two copies

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11
Q

What are the consequences of chromosomal imbalance?

A
  • Recurrent miscarriages
  • Relative infertility
  • Malformations/intellectual disability in relatives
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12
Q

What is the frequency of reciprocal translocations?

A

1 in 600

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13
Q

Fill in the blank: The short arms of acrocentric chromosomes house _______.

A

repetitive, duplicated DNA

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14
Q

What are the characteristics of the long arm and short arm in chromosome nomenclature?

A
  • Long arm: q
  • Short arm: p
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15
Q

What is the population incidence of Down syndrome?

A

1:700

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16
Q

What is the risk of recurrence for whole chromosomal monosomy X?

A

Negligible

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17
Q

What does the term ‘derivative chromosome’ refer to in karyotype nomenclature?

A

der

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18
Q

What is the significance of the terms ‘+’ and ‘-‘ in karyotype nomenclature?

A
  • ’+’ indicates gain of a whole chromosome
  • ’-‘ indicates loss of a whole chromosome or part
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19
Q

What is the main challenge in chromosomal analysis?

A

Distinguishing pathogenic copy number variants from ‘normal’ background variation

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20
Q

What are the types of chromosomal structural alterations?

A
  • Duplications
  • Deletions
  • Insertions
  • Translocations
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21
Q

What is the clinical management for Klinefelter syndrome?

A
  • Testosterone replacement
  • Fertility treatment options
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22
Q

What are the clinical patterns of presentation for intellectual disability?

A
  • Prenatally
  • Postnatally
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23
Q

True or False: Non-disjunction can occur during anaphase I or meiosis II.

A

True

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24
Q

What are some features of the sex chromosomes?

Study These Flashcards
A
  • Males: one copy of X genes + one copy of Y genes
  • Females: two copies of X, but one X has 80% of its content inactivated
25
What is the diagnostic technique used to identify Down syndrome?
* Metaphase karyotype * Interphase FISH * Chromosomal microarray * Whole genome sequencing
26
What is the term for a balanced transfer of material from one chromosome to another?
Reciprocal translocations
27
Fill in the blank: The process of chromosome loss in Turner syndrome is thought to be _______.
postzygotic
28
What is the expected outcome of balanced reciprocal translocations?
Most have no effect in balanced state
29
What can chromosomal microarray reveal about chromosomes?
High resolution reveal we are all 'unbalanced'
30
What is the importance of chromosome length in viability?
The length of imbalance is inversely correlated with viability
31
What is the role of maternal serum markers in prenatal screening?
To assess risk for genetic anomalies
32
What is the significance of cell-free placental DNA in maternal blood?
It allows non-invasive prenatal screening for genetic anomalies
33
What are the two copies of chromosomes that females possess?
Two copies of the X chromosome, but one X has 80% of its content inactivated.
34
What can chromosomal abnormalities cause?
Loss or gain of genes, often resulting in disease due to cell death and/or abnormal growth.
35
What does chromosomal microarray reveal?
High-resolution chromosomes that show we are all 'unbalanced'.
36
What colors represent deletions and duplications in chromosomal microarray?
Deletions are shown in red, duplications in blue and green.
37
What is the challenge in distinguishing pathogenic copy number variants?
Differentiating them from 'normal' background variation in the general population.
38
What are the clinical indications for assessing chromosomal structure?
* Abnormality of growth or development (a syndrome) * Intellectual disability * Recurrent miscarriage * Investigation of cancers (e.g. leukaemia)
39
What is Turner syndrome characterized by?
* Neonatal oedema/webbed neck * Coarctation of the aorta * Linear growth delay * Primary amenorrhoea
40
What is the incidence rate of Turner syndrome?
1:3000.
41
What is the karyotype in 75% of Turner syndrome cases?
45,X0 karyotype.
42
What causes Turner syndrome?
* 75% have a 45,X0 karyotype * 25% have a structural abnormality of one X chromosome
43
What is the recurrence risk of Turner syndrome?
Negligible due to post-zygotic mechanisms.
44
What is the karyotype of Klinefelter syndrome?
47,XXY.
45
What are the features of Klinefelter syndrome?
* Reduced testicular function * Tall stature * IQ in the normal range (but slightly left-shifted)
46
What is the incidence of Klinefelter syndrome?
1:500-1000.
47
What management is used for Klinefelter syndrome?
* Testosterone replacement * Fertility treatment options
48
What are some clinical patterns for assessing intellectual disability?
* Prenatally * Postnatally
49
What are the methods for diagnosing Down syndrome?
* Metaphase karyotype * Interphase FISH * Chromosomal microarray * Whole genome sequencing
50
What is the genetic basis of Down syndrome?
* Free-standing trisomy 21 * Robertsonian translocations * Post-zygotic occurrences
51
What is the population incidence of Down syndrome?
1:700.
52
What does non-invasive prenatal screening detect?
Genetic anomalies, including trisomy 21.
53
What is the process for analyzing cell-free placental DNA?
Fragments are isolated from maternal serum, sequenced, and the number of fragments is counted.
54
What are the clinical consequences of carrying a chromosomal rearrangement in recurrent miscarriage?
* Recurrent miscarriages * Relative infertility * Malformations/intellectual disability in relatives
55
What is the frequency of reciprocal translocations?
1 in 600.
56
What are the keys to thinking regarding recurrent miscarriages?
* History of recurrent miscarriages * Consider wider family history * Check for carrier status using karyotype * Check for imbalance with chromosomal microarray
57
What is the main technique used to analyze chromosomal balance?
Chromosomal microarray.
58
What can sex chromosome aneuploidies lead to?
Disparate and complex phenotypes.
59
What can balanced translocations result in?
Familial presentations of chromosomal disorders in offspring.

MICN201 2025 Genetics (9 decks)

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