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BIO227 Human Genetic Disorders > Week 2 > Flashcards

Week 2 Flashcards

1
Q

What is aneuploidy

A

Abnormal number of chromosomes in a haploid set

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2
Q

Clinical features in the newborn period

A

Hypotonia
Sleepiness
Excess nuchal skin

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3
Q

Craniofacial clinical features of DS

A

Brachycephaly - shorter skull
Epicanthic folds - skin fold of the upper eye covering the inner eye corner
Protruding tongue
Small ears
Upward sloping palpebral fissures

Strabismus - eyes point in diff directions

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4
Q

Clinical features of DS in limbs

A

Single palmer crease
Small middle phalanx on the fifth finger
Wide gap between first and second toes

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5
Q

Clinical features of DS - cardiac

A

Atrial and ventricular septal wall defects

Common AV canal

Patent ductus arteriosus - persistent opening between two blood vessels leading from the heart

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6
Q

What is atresia in DS

A

narrowing
Anal atresia and duodenal atresia are clinical features of DS

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7
Q

What is hirschsprung disease

A

Stool stuck in bowels
A clinical feature of DS

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8
Q

IQ in DS children

A

Have a broad range
25-75

Normal - 40-45

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9
Q

Social skills in DS children compared to normal

A

Relatively happy, advanced and affectionate

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10
Q

Average height in DS patients

A

150 cm

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11
Q

Life expectancy in DS patients

A

50-60 years
15-20% of heart affected DS patients have an early death

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12
Q

Alzheimer’s relation to DS

A

Early onset Alzheimer’s is common in DS patients - 2-3 decades earlier

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13
Q

Development of Alzheimer’s

A
  1. Shrinkage of cerebral cortex + enlarged ventricles
  2. Amyloid beta plaques
  3. Tau neurofibrillary tangles
  4. Amyloid precursor protein
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14
Q

How does amyloid precursor protein contribute to Alzheimer’s

A

Beta and gamma- secretase abnormally cleave onto APP

Which generates beta amyloid peptides

Which accumulate into neurotoxic amyloid plaques in the brain tissues

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15
Q

What is the main chromosomal cause of DS

A

Meitotic non-disjunction (90%)
- error in cell division meiosis 1
- causes trisomy in chromosome 21
- mechanism = one chromosome pair fails to split into two

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16
Q

Other chromosomal causes of DS

A
  • mitotic non-disjunction
  • robertsonian translocation
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17
Q

What is screening

A

Test applied to a whole population
Identifies those at high risk

18
Q

What is a diagnostic test

A

More specific test that identifies those who have the disease

19
Q

How does screening in DS work

A

Pregnant women are offered a screening test
Using an algorithm a probability is calculated
If P > 1/150, a diagnostic test is offered

20
Q

What are the methods of screening used for DS

A
  1. Ultrasound
  2. Serum markers
  3. Cell free foetal DNA
  4. Non invasive prenatal testing
21
Q

How is ultrasound used for DS

A

Identifies the nuchal translucency feature

22
Q

What bio markers are used for serum marker screening test used for DS screening

A

2 bio markers are used
- low pregnancy associated plasma A
- high human chorionic gonadotropin hCG

23
Q

How are serum markers used to screen DS

A

Quadruple test
1. Decreased alpha fetoprotein
2. Decreased unconjugated estriol
3. Elevated hCG
4. elevated inhibit A

Triple test - inhibit A is not included

P>1/150 - diagnostic test is offered

24
Q

mitotic non-disjunction

A

failure of two chromosomes to separate during mitosis
so both go to one daughter cell

25
Q

robertsonian translocation

A

an acrocentric chromosome joins end to end with another

26
Q

why non disjunction increases with maternal age

A

cohesion between sister chromatids deteriorate

missegragation of recombinant chromosomes

meitotic spindle aberrations

efficiency of kinetochore

shortening of telomeres

reduced blood flow to oocytes

27
Q

what is mosaicism in DS

A

when a person has two or more genetically different sets of cells in their body

so in DS not all cells have the extra chromosome 21

28
Q

what is the presentation of mosaic DS

A

fewer DS features

29
Q

what is an acrocentric chromosome

A

the centromere is pushed toward the end of the chromosome

30
Q

what is a satellite structure

A

the remaining short arms after a robertsonian translocation

31
Q

HSA21 gene relation to DS

A

genes on the long arm of chromosome 21
15% functional

DS caused by over-expression of HSA21 in trisomic cells

32
Q

how is DS disordered gene expression

A

HSA21 is over-expressed

other genes have dysregulation

so whole genome is affected

33
Q

what is XIST

A

X inactive specific transcript

a non coding RNA transcript on the X chromosome

34
Q

what is the barr body

A

an inactivated X chromosome

35
Q

what does XIST do

A

it induces heterochromatin changes
= compaction/condensation

into the Barr body

36
Q

method to use XIST to inactivate chromosome 21

A
  1. fibroblasts treated back into induced pluripotent stem cells
  2. then XIST gene is introduced
  3. they are turned on by the Doc mechanism
  4. XIST is then produced which inactivates the chromosome
37
Q

biological implications of using XIST to inactivate chromosome 21

A

positively impacts intellectual disability

silencing leads to faster differentiation of neural progenitor cells

38
Q

what is dup-app

A

chromosomal region on APP gene that is duplicated

dup-app individuals tend to develop alzeimers early

39
Q

how is dup-app related to down syndrome

A

in comparison to DS, dup-APP individuals develop dementia earlier

this suggests that the extra chromosome is not the only contributing factor

leads to the neuroprotective hypothesis

40
Q

what is the neuroprotective element hypothesis

A

BACE2 is another gene
a homolog of beta secretase

it is suggested that BACE2 acts antagonistically to beta secretase

which results in less formation of beta amyloid

41
Q

what chromosome are tau tangles on

A

17

not 21

BIO227 Human Genetic Disorders (6 decks)

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