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EMS - GiM > (16+17) Huntington's Disease > Flashcards

(16+17) Huntington's Disease Flashcards

1
Q

What is Huntington Disease (HD)?

A

Progressive neurodegenerative disorder with motor, cognitive and psychiatric disturbances. Affects movements, memory and mood

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2
Q

In what ways does HD affects movement?

A
  • chorea
  • dystonia
  • bradykinesia
  • swallowing/choking
  • dysarthria
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3
Q

What is chorea?

A

A neurological disorder characterized by jerky involuntary movements affecting especially the shoulders, hips, and fac

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4
Q

What is dystonia?

A

A state of abnormal muscle tone resulting in muscular spasm and abnormal posture

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5
Q

What is bradykinesia?

A

Bradykinesia means slowness of movement. Weakness, tremor and rigidity may contribute to but do not fully explain bradykinesia

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6
Q

What is dysarthria?

A

Difficult or unclear articulation of speech that is otherwise linguistically normal

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7
Q

In what way does HD affect mood?

A
  • depression
  • euphoria
  • apathy
  • anxiety
  • aggression
  • psychotic symptoms
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8
Q

In what way does HD affect cognition?

A
  • loss of executive functioning
  • rigidity of thought
  • memory loss
  • dementia
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9
Q

What is the mean age of onset of HD?

A

35 to 44 years (range 2-80 years)

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10
Q

What is the median survival time of HD?

A

15 to 18 years after onset

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11
Q

What type of genetic disorder is HD?

A

Autosomal dominant

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12
Q

Does HD have complete or incomplete penetrance?

A

Complete

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13
Q

Where is the HTT gene?

A

4q16.3

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14
Q

What does a normal HTT gene contain?

A

A run of CAG trinucleotide repeats within exon 1

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15
Q

What does the HD mutation in the HTT gene consist of?

A

An expansion of the CAG repeats (>40 repeats)

a few people develop HD with CAG repeats of 36-39

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16
Q

What is the normal Huntingtin protein?

A

3144 amino acids

Widely expressed in different tissues - function unknown

17
Q

What does the abnormal HD protein contain?

A

Increased number of glutamine amino acids = polyglutamine (polyO) expansion which alters protein structure and biochemical properties

18
Q

What are the aggregates in HD?

A

PolyO cellular protein aggregates - unknown if they cause disease

19
Q

Basal ganglia is affected in HD. Which part of the basal ganglia especially?

A

Caudate nucleus

20
Q

Anticipation is a phenomenon associated with which type of disorders?

A

Triplet repeat disorders

21
Q

Why are triplet repeat disorders associated with anticipation?

A

Triplet repeat disorders are unstable and may increase (occasionally contract) when passed to the next generation

22
Q

The phenomenon of anticipation is often linked to what?

A

The gender of the parent

23
Q

Huntington disease has high anticipation risk when inherited from whom?

A

Paternal inheritance

24
Q

Myotonic dystrophy has high anticipation risk when inherited from whom?

A

Maternal inheritance

25
Q

Fragile X syndrome has high anticipation risk when inherited from whom?

A

Maternal inheritance

26
Q

What is the mode of inheritance of fragile X syndrome?

A

XL recessive

27
Q

What is the mode of inheritance of myotonic dystrophy?

A

AD

28
Q

How is HD triplet repeat size related to age of onset?

A

The higher the CAG trinucleotide repeat number, the lower the age at neurological onset

29
Q

If somebody had symptoms of HD, which gene test would be appropriate?

A

Diagnostic gene test

30
Q

If somebody was asymptomatic for HD, which gene test would be appropriate?

A

Predictive gene test

31
Q

What is predictive testing?

A

The use of a genetic test in an asymptomatic person to predict future risk of disease

32
Q

In which other diseases (other than HD), is predictive gene testing possible?

A
  • BRCA (familial breast cancer gene)
  • HNPCC (hereditary non-polyposis colon cancer)
  • myotonic dystrophy
33
Q

What treatments are available for HD?

A
  • symptomatic treatment only at present
  • no prevention or cure
  • testing does not save lives
34
Q

What reasons may be given for wanting HD predictive testing?

A
  • just ‘want to know’
  • plan future care
  • want to plan their career
  • make decisions about children
  • inform other relatives whose risk may change
35
Q

Does HD predictive testing give a certain result?

A

If negative - complete certainty

If positive - certainty as fully penetrant

But cannot tell age of onset, course, severity

36
Q

What must be considered when choosing to have HD predictive testing?

A
  • insurance
  • changing risk to others
  • impact on current and future relationships
  • psychological impact
  • no medical advances yet
37
Q

How many drop out of HD predictive testing?

A

50-60%

EMS - GiM (14 decks)

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