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(YEAR 1) PBLs > FunMed: PBL 3 (Imprinting - Prader Willi Syndrome) > Flashcards

FunMed: PBL 3 (Imprinting - Prader Willi Syndrome) Flashcards

1
Q

Define genomic imprinting

A

Epigenetic phenomenon where certain genes are expressed in a parent-of-origin-specific manner. If the allele inherited from the father is imprinted, it is thereby silenced, and only the allele from the mother is expressed. Silent gene is methylated

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2
Q

What is hypothyroidism?

A

Abnormally low activity of thyroid gland –> retardation of growth and mental development in children and adults

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3
Q

What is SNRPN?

A

Small nuclear ribonucleoprotein-associated protein N; plays a role in pre-mRNA processing

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4
Q

What is a chromosomal microarray?

A

a set of DNA sequences representing the entire set of genes of an organism, arranged in a grid pattern and used in genetic testing

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5
Q

Describe the symptoms of Prader Willi Syndrome

A

Birth: hypotonia and poor sucking reflex due to lack of muscle tone
Childhood: developmental defects, excessive sleeping, overeating and delayed puberty
Aduthood: hypogonadism and prone to diabetes

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6
Q

Describe the symptoms of Angelman Syndrome

A

“Happy puppet syndrome” - intellectual and developmental disability, speech impairment, seizures, jerky movements and frequent laughter and smiling

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7
Q

What is the difference between PWS and AS?

A 
PWS = due to imprinting/silencing of maternal chromosome
AS = imprinting/silencing of paternal chromosome
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8
Q

What is the cause of Prader Willi Syndrome?

A

Deletion of q11-13 region of paternal chromosome 15 OR maternal uniparental disomy (UPD) with lack of paternal chromosome 15. This syndrome occurs because there is imprinting on the maternal chromosome 15 (silencing)

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9
Q

What is the cause of Angelman Syndrome?

A

Deletion of q11-13 region of the maternal chromosome 15 or paternal uniparental disomy

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10
Q

What are the proposed reasons for genomic imprinting?

A

Ovarian time bomb theory - imprinting involved to prevent spontaneous development of unfertilised eggs
Genetic conflict hypothesis - strikes a balance between some genes e.g. paternal imprinting –> larger offspring, maternal offspring –> smaller offspring

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11
Q

What are the symptoms of Beckwith-Wiedemann (foetal overgrowth) syndrome?

A

Large tongue, larger birth weight, rhabdomyosarcoma

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12
Q

What is the cause of Beckwith-Wiedemann syndrome?

A

Paternal uniparental disomy of chromosome 11

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13
Q

What support is available to support a child with chronic illness?

A

Learn about illness, support group, face possibility of early death, maintain open and honest communication, share leadership and include all family members in decision making

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14
Q

What treatment is there for Prader Willi Syndrome?

A

No cure; speech therapy, structurelearning involvement, prevention of over-feeding and growth hormone injections (daily) to support linear growth and increase muscle mass

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15
Q

What mechanisms are involved in imprinting?

A

DNA methylation and histone modification

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16
Q

Describe the process of DNA methylation

A

Attachment of methyl (CH3) groups to the bases of DNA at cytosines that follow guanine (CpG dinucleotides)

17
Q

Describe the process of histone modification

A

Histone acetyl transferases may acetylate lysine in core histones (transcriptional activation) or histone deacetylases may remove lysine residues (deactivate transcription)

18
Q

Define epigenetics

A

Study of changes in organisms caused by modification of gene expression rather than alteration of genetic code itself

19
Q

Describe what is meant by ‘uniparental disomy’

A

Receiving two copies of a chromosome from one parent and none from the other

20
Q

Describe how methylation-specific PCR can diagnose PWS or AS.

A

PCR can be conducted in SNRPN region of q11-13 region of chromosome 15:
PWS: methylation of maternal chromosome in comparison to control
AS: methylation of paternal chromosome in comparison to control

21
Q

What disease can become more prevalent in children whose parents are consanguineous?

A

Autosomal recessive genetic disorders can become manifest as two heterozygotes can generate a homozygous child.

22
Q

What does non-consanguineous mean?

A

A union between two individuals who are not related as second cousins or closer

23
Q

Why may there be increased stress in a family where there is a child with chronic illness?

A

Financial concerns (treatment expense), parent unable to work or relax (constant care), distress from seeing child in pain/suffering, sense of no hope or entrapment if there is no cure

24
Q

Which chromosome is involved in causing both Prader Willi and Angelman syndromes?

A

q11-13 region of chromosome 15

25
Q

What is the significance of the SNRPN gene?

A

It’s the region which is affected by methylation to produce either AS or PWS

26
Q

How are histones involved in gene expression?

A

Control coiling and uncoiling of DNA to allow transcription (or not)

27
Q

What is the role of histone acetyl transferases (HAT)?

A

Acetylate the lysine residues in core histones –> less compact, transcriptionally active chromatin

28
Q

What is the role of histone deacetylases (HDAC)?

A

Remove acetyl groups from lysine residues in core histones –> condensed, transcriptionally silences chromatin

29
Q

What are the characteristics of an imprinted gene?

A

CpG islands, nucleosomal condensation (due to deacetylation) and methylation

30
Q

What indicates transcriptional competence?

A

Binding of transcription complex

31
Q

What are the characteristics of a transcriptionally active gene?

A

Opening of chromatin by acetylation and there is demethylation

32
Q

How is methylation involved in germ cell development?

A

Primordial germ cells are demethylated (activated) early in development, and sperm and oocytes are remethylated (prevent spontaneous development)

33
Q

How does methylation-specific PCR work?

A

Bisulfite is added to a sample of DNA from an individual, and the non-methylated (active)cytosine (C) bases will be converted to uracil, and after PCR will become thymine (T) whereas methylated (transcriptionally active) C is unchanged, and this can be analysed

(YEAR 1) PBLs (29 decks)

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