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ME2308 Principles of Disease > chromosome abnormalities, mutations and analysis mw % + > Flashcards

chromosome abnormalities, mutations and analysis mw % + Flashcards

1
Q

Name the categories of chromosomal abnormalities?

A
  • Numerical
  • Structural
  • Mutational
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2
Q

Incidence of chromosomal abnormalities

A
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3
Q

First trimester miscarriages

A
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4
Q

Liveborn infants

A
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5
Q

Origins of chromosome abnormalities:
non-disjunction

A
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6
Q

Trisomy 21 (Down syndrome)

A

–Incidence: 1 in 650 to 1 in 700

–Average life expectancy (50-60 years)

–Alzheimer’s disease in later life

  1. Chromosomal findings
  • Trisomy 21: non-dysjunction (95%), usually maternal origin
  • Unbalanced Robertsonian translocation (4%)
  • Mosaicism (1%)
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7
Q

Trisomy 13 (Patau syndrome)

A

–Incidence: 1 in 5000

–Multiple dysmorphic features and mental retardation

–About 5% die within first month, very few survive beyond first year

–Non-dysjunction (90%), maternal origin

–Unbalanced Robertsonian translocation (10%)

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8
Q

Trisomy 18 (Edwards syndrome)

A

–Incidence: 1 in 3000

–Severe developmental problems; most patients die within first year, many within first month

–Non-disjunction (90%), maternal origin

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9
Q

45,X (Turner syndrome)

A

–Incidence: 1 in 5000 to 1 in 10000 (liveborn)

–Incidence at conception much greater, about 97% result in spontaneous loss

–Females of short stature and infertile

–Neck webbing and widely spaced nipples

–Intelligence and lifespan is normal

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10
Q

47,XXY (Klinefelter syndrome)

A

–Incidence: 1 in 1000

–Tall stature, long limbs

–Male but infertile, small testes, about 50% gynaecomastia

–Mild learning difficulties

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11
Q

Describe structural abnormalities?

A
  • Balanced or unbalanced rearrangements
  • Translocations

–Reciprocal: involving breaks in 2 chromosomes with formation of 2 new derivative chromosomes

–Robertsonian: fusion of 2 acrocentric chromosomes

Note: Acrocentric chromosome: A chromosome in which the centromere is located quite near one end of the chromosome.

  • Deletions
  • Insertions
  • Inversions
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12
Q

Reciprocal translocation carrier:
outcomes (pic)

A
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13
Q

Robertsonian translocation (pic)

A
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14
Q

Robertsonian translocation carrier:
outcomes (pic)

A
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15
Q

What are the types of mutations?

A
  • Non-coding
  • Coding

–Silent

–Missense

–Nonsense

–Frameshift

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16
Q

What is a silent mutation?

A
  • CGA (Arg) to CGC (Arg). Same amino acid
17
Q

What is a missense mutation?

A
  • CGA (Arg) to GGA (Gly). Different amino acid
18
Q

What is a nonsense mutation?

A
  • CGA (Arg) to TGA (Stop). amino acid ⇒ stop codon
19
Q

What is a frameshift mutation?

A
  • Frameshift – deletion / insertion
    e. g. CGA (Arg) to CCGA (Pro, then out-of-frame)
20
Q

Mutation nomenclature?

A
  • Green = exons, black line = introns
  • Cys64Arg ⇒ Cys replaced with Arg at 64
  • M252X ⇒ M is replaced with a stop codon
  • 1294del40 ⇒ 40 are deleted from 1294
  • 662-42C>T ⇒ At 662 - 42, C is replaces T
  • IVS2 + 12INSG ⇒ At Intervening Sequence 2, + 12, a G is added (intron)
  • 1298A>G ⇒ A replaces G at 1298
21
Q

How do you detect mutations?

A
  • Polymerase chain reaction (PCR)
  • Gel electrophoresis
  • Restriction fragment length polymorphism (RFLP) analysis
  • Amplification refractory mutation system (ARMS)
  • DNA sequencing
22
Q

PCR

A

•In vitro technique

Essentials

  • Sequence information
  • Oligonucleotide primers
  • DNA
  • Nucleotides
  • DNA polymerase
23
Q

Gel electrophoresis

A

Technique

  • Separate DNA fragments by size
  • Apply an electric field
  • DNA is negatively charged, so moves towards postive end
  • Separate through agarose gel matrix
  • Visualise DNA fragments

Applications

  • DNA cloning & sequencing
  • In vitro mutagenesis
  • Gene identification
  • Gene expression studies
  • Forensic medicine
  • Typing genetic markers
  • Detection of mutations
24
Q

Gel elc (pro-cons)

A

Advantages

  • Speed
  • Ease of use
  • Sensitive
  • Robust
25
Q

ARMS (Amplification Refractory Mutation System)

A

ARMS is an application of PCR in which DNA is amplified by allele specific primers.

Advantages

  • Cheap
  • Labelling not required

Disadvantages

  • Electrophoresis required
  • Primer design critical
26
Q

Restriction endonuclease

A
  • Enzymes from bacterial cells
  • Degrade DNA of invading viruses
  • Recognise specific DNA sequences
  • Usually 4-8 bp
  • Always cut DNA at the same site
27
Q

DNA sequencing

A
  • Chain termination method (Sanger)
  • Use of dideoxynucleotides

Advantages

  • Gold standard for mutation detection
  • Automation and high throughput

Disadvantages

  • Expensive equipment
  • Poor quality sequence read

–First part of sequence (15 to 40 bases)

–Deterioration after 700-900 bases

ME2308 Principles of Disease (40 decks)

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