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CSP 3 > Single gene disorders > Flashcards

Single gene disorders Flashcards

1
Q

Define single gene disorder

A

Any genetic disorders caused by a change affecting only one gene

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2
Q

What kind of genetic pattern do they tend to follow

A

Mandelian (AD, AR etc,)

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3
Q

What kind of single gene mutations are possible

A

Missense mutations
Nonsense mutations
Frame-shift mutations

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4
Q

What epigenetic mutations are possible

A 
DNA methylation
Chromatin modifications
Deletions
Insertions
Inversions
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5
Q

How was the gene responsible for SCD seen for the first time in the 50s

A

Studying the protein and determining the amino acid change

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6
Q

What molecular biology methods can be used to identify single gene disorder

A
  • Linkage analysis

- Positional cloning

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7
Q

Why are rare monogenic diseases difficult to detect by linkage analysis

A

Due to locus heterogeneity (mutations in

different genes resulting in the same clinical picture).

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8
Q

What is meant by X-linked recessive disorder?

A

Mostly male, born to carrier mothers
Half of the sons affected
Daughters of an affected fathers are carriers, never from father to son

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9
Q

Give 4 examples of X-linked recessive disorders?

A

1- Haemophilia A
2- X linked severe combined immune disorder
3- Duchenne muscular dystrophy
4- Becker muscular dystrophy

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10
Q

What is the role of dystrophin

A

Precise role unknown

- Appears to stabilise sacrolemma, protect muscle fibres from long term contraction- induced damage and necrosis

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11
Q

In Duchenne Muscular Dystrophy, what is wrong with the dystrophin gene

A

Absent or non funcctional due to a p21 mutation

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12
Q

When does DMD present? What is the life expectancy?

A

3-5 years

Mean life expectancy mid 20s

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13
Q

Does cardiomyopathy precede or follow skeletal progression in DMD

A

Follows

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14
Q

What is deficient in Haemophilia A

A

Clotting factor VIII

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15
Q

What is deficient in X linked SCID

A

Very few T cells and NK cells

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16
Q

What receptors are affected in SCID

A

IL2 and IL7 receptors

17
Q

Give 3 examples of X-linked dominant disorders

A
  • Some forms of retinitis pigmentosa
  • Chondrodysplasia Punctat
  • Hypophosphatemic rickets
18
Q

Give 4 examples of autosomal recessive disorders

A

Phenylketonuria
Tay-Sachs
Haemochromatosis
Cystic Fibrosis

19
Q

Give 4 examples of autosomal dominant disorders

A
  • Huntington Disease
  • Achondroplasia
  • Polycystic kidney disease
  • Werner mesomelic syndrome
20
Q

What genetic change happens in Huntington disease

A

CAG expansion

21
Q

What characterises Werner Mesomelic syndrome

A

Hypo/ aplasia of the tibiae
Preaxial polydactyly of the hands/ feet
Five fingers hand with absence of thumbs

22
Q

What is meant by an Y-linked dominant disease

A

Only males affected, passes from father to son/ No generation skipped

23
Q

Give an examplle of a Y lilnked dominant condition

A

Retinitis pigmentosa

24
Q

Which is meant by genetic imprinting

A

Epigenetic phenomenon by which certain genes are expressed; imprinting silences the gene. If the father’s gene is imprinted only the mother’s is expressed

25
Q

Give 3 examples of imprinting conditions

A
  • Beckwith- Wiedemann Syndrome
  • Prader- Willi Syndrome
  • Angelman syndrome
26
Q

What are the features of beckwiwth-wiedeman syndrome

A

Large size, predisposition to tumours

27
Q

What are the features of Prader- Willi syndrome

A

Low muscle tone, cognitive probs

28
Q

What is Angelman syndrome?

A

Neuro-genetic disorder characterised by severe intellectual and development disability, sleep disturbance and serizures

29
Q

Name the genes involved in Angelman syndrome

A

HSA15

PWS

30
Q

Describe how Angelman syndrome is inhertied

A

Both sexes affected
Only when a mutation chromosome is maternally inherited
If mother is carrier then chance of inheritance is 50%

31
Q

Give 4 examples of mitochondrial conditions

A

Mitochondrial myopathy
Diabeties mellitus and deafness
Leber’s hereditary optic neuropathy
Leigh syndrome

32
Q

What is gene therapy

A

Introduction of normal genes into cells in place of missing or defective ones in order to correct genetic disorders

33
Q

When is gene therapy more possible

A
  • Recessive
  • Loss of function
  • Tissue accessible
  • Small gene
34
Q

What are the 3 steps of dystrophin gene mutation

A

1- Disruption of the splicing acceptors to skip exon 45
2- Introduced of small indels to modulate the protein reading frame
3- Knockin of the missing exon 44 to resore full protein coding region

35
Q

What technique could be used in the future to correct single gene disorders

A

CRISPR-Cas 9

CSP 3 (9 decks)

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