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MCBG > Chromosomal Abnormalities > Flashcards

Chromosomal Abnormalities Flashcards

1
Q

What is Cytogenetics?

A

Study of genetic constitution of cells through the visualisation and analysis of chromosomes

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2
Q

Why do cytogenetic analysis?

A

Accurate diagnosis, better clinical management, assess future reproductive risks, prenatal diagnosis

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3
Q

Why might you be referred for cytogenetics?

A

Constiutional abnormalities, prenatal disagnosis, birth defects, abnormal sexual development, infertility, recurrent fetal loss, leukaemia, solid tumours, specific translocations/abnormalities

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4
Q

What are the two types of prenatal diagnosis?

A

Chorionic villus and Amniocentesis

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5
Q

What can be seen in prenatal diagnosis?

A

Maternal screening for down syndrome, first trimester screening, FH chromosome abnormality, Abnormal ultrasound scan, DNA studies

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6
Q

What birth defects can be seen on prenatal scan?

A

Dysmorphism, congenital malformations, mental retardation, developmental delay, specific syndromes like down, williams and digeorge syndrome,

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7
Q

At what stage are chromosomes karyotypes?

A

Metaphase

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8
Q

How do you analyse chromosomes?

A

Count the number of chromosomes, identify each chromosome pair, assess if there is any missing or extra material,must be seen at correct resolution twice and be independently rechecked once

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9
Q

How do you describe a karyotype?

A

chromosome number, sex complement and structural changes, separated by commas e.g. 46, XX- normal female

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10
Q

What are Trisomies?

A

Extra chromosome e.g. down syndrome

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11
Q

What are monosomies?

A

Less chromosomes e.g. turner syndrome

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12
Q

What is polyploidy?

A

Gain of a whole haploid set of chromosomes

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13
Q

What causes polyploidy?

A

polyspermy- when an egg is fertilised by more than one sperm

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14
Q

What is anaphase lag?

A

Chromosomes left behind and not pulled to poles

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15
Q

What are the symptoms of down syndrome?

A

Hyptonia, characteristic, facial features, heart defects, increased chance of leukaemia, alzeimers

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16
Q

Which chromosome is trisomy in down syndrome?

A

21

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17
Q

What chromosome is trisomy in Edwards syndrome?

A

18

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18
Q

What are the symptoms of Edwards Syndrome?

A

Small lower jaw, prominent occiput, low-set ears, rocker bottom feet, overlapping fingers, live 5-15 days

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19
Q

What chromosome is Trisomy in Patau syndrome?

A

13

20
Q

What is X chromosome inactivation?

A

One X chromosome is ever active in a human cell

21
Q

Why does Turners syndrome occur?

A

Monosonic for genes in the Par regions

22
Q

What are the symptoms of Turners syndrome?

A

Puffy feet, redundant skin at back of neck, short, heart defects, mild learning difficulties, neck webbing, infertile

23
Q

What is Mosaicism?

A

Presence of two or more cell lines in an individual

24
Q

What usually causes mosaicism?

A

Mitotic non-disjunction

25
Q

What is a reciprocal translocation?

A

Two break arrangement, carriers will produce balanced and unbalanced gametes, will have abnormal phenotype if unbalanced

26
Q

What are the types of secregation in Meiosis?

A 
Alternate- balanced
Adjacent 1- non homologous centromeres
Adjacent 2- homologous centromeres
3:1 non disjunction
4:0 non disjunction
27
Q

How do you assess unbalanced segregation outcomes?

A

Establish the likely segregation, see if the imbalances have been reported before, quote risk if established

28
Q

What is a robertsonian translocation?

A

Two afrocentric chromosomes fused together- carrier is phenotypically normal but child will not be

29
Q

When does prenatal aneuploidy screening take place?

A

Interphase

30
Q

What occurs in prenatal aneuploidy screening?

A

14 days in culture which causes anxiety, FISH

31
Q

What can microarray not detect?

A

Balanced rearrangments

32
Q

Who would be referred for a microarray?

A

learning difficulties, normal karyotype to see if its really balanced and unbalanced karyotypes to assess gene control

33
Q

What are the positives of microarray?

A

examines whole genome at a high resolution, targeted against known genetic conditions, equivalent to 1000s of fish investigations, detailed info on del/dup regions, better phenotype and genotype correlation

34
Q

What are the negatives of microarray?

A

more expensive than karyotyping, do not detect balanced rearrangements, masaicism may be missed, copy number variation

35
Q

How do deletions and duplications arise?

A

Uneven pairing and recombination during meiosis

36
Q

How would you report abnormal chromosome results?

A

Give the ISCN
Describe abnormality in works and what it means, relate to clinical problem, request family samples if requires, refer to clinical genetics, provide appropriate literature

37
Q

What is Uniparental disomy?

A

Homologous chromosomes from one parent

38
Q

Why is UPD a problem?

A

Imprinting

39
Q

What syndromes are caused by UPD?

A

Prader-willi, Russell-Silver and Beckwith-Wiedemann

40
Q

How does UPD occur?

A

Trisomy rescue, monosomy rescue, gamete complementation, mitotic error

41
Q

What is NGS?

A

Next generation sequencing- sequence fragments in parallel, reveals entire genomes DNA

42
Q

What are the positive of NGS?

A

Increased read length, high throughput, automated workflow, simplified protocols

43
Q

What are the negatives of NGS?

A

Whole genome sequencing costs high, insufficient IT capacity, lack of knowledge to fully interpret findings, ethically

44
Q

How is non-invasive prenatal testing done?

A

Uses cell free metal DNA in maternal plasma

45
Q

What are liquid biopsies used for?

A

Non invasive cancer testing

MCBG (19 decks)

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