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Flashcards in week 10 --> HD Deck (26)
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What is huntington disease?

Progressive neurodegenerative disorder with motor, cognitive, pysychiatric disturbance.
Affects mood, movement and memory


What are the movement disorders caused by HD?

Chorea, dystonia, bradykinesia, swallowing/ choking, dysarthria


What are the mood disorders caused by HD?

Depression, euphoria, apathy, anxiety, aggression, psychotic symptoms


What are the cognition disorders caused by HD?

Loss of executive functioning, rigidity of thought, memory loss, dementia


What is the median age onset of HD and how survival time after diagnosis?

Mean age of onset is 35 to 44 years but can range from 2-80yrs.

Median survival rate is 15-18 years after onset


What does Chorea mean?

Uncrotrolled movemement that you are not expecting to make --> no purpose


What is the genetic cause of HD?

Autosomal dominant disorder
Complete penetrance --> everyone that inherit the genetic mutation will get it

HTT gene at 4q16.3

Normal HTT gene contains, within exon 1, a run of CAG trinucleotide repeats


What happens to the CAG trinucleotide repeat in a person with HD?

The HD mutation causes expansion of the CAG repeat to be greater than 40. Which is seen as the cut of point for the caue of HD.

Very few cases of 36-39 CAG repeats causing HD.


What is the action of HD at protein level?

Abnormal protein – increased number of glutamine amino acids = polyglutamine (polyQ) expansion which alters protein structure and biochemical properties.

PolyQ cellular protein aggregates form – unknown if they cause disease


Where in the brain does the abnormal proteins formed by the HD mutation affect?

Basal gnaglia especially caudate nucleus primarily affected


What is a definition of anticipation?

The onset of a disorder occurs at an earlier age as it is passed from one generation to the next. Often this is associated with an increase in severity of symptoms


What is anticipation assoicated with?

Assoicated wtih triplet repeat disorders


What is the consequence of anticpiation on triplet repeat disorders?

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


The phenomenon of anticipation is often linked to the gender of the parent. State the high anticipation risk for Hd, Myotonic dystropy and Fragile X syndrome.

Also state the mode of inheritance?

HD--> Autosomal dominant inheritance --> higher anticipiation risk if its from parternal inheritance.

MD --> AD inheritance --> Maternal inheritance

Fragiel X syndrome --> XL recessive --> maternal inheritance


What affects the age of onset of HD?

The size of expansion of CAG repeat


When is predictive gene testing used for HD?

When the patient is aymptomatic but has a family history of HD. So trying to predict whether or not the person with get HD


What is investigated in gene testing for Hd?

The number of CAg repeats


What is HD predictive testing?

Different to convential medical testing which defines a person current condition.

It is testing someone who is asymptomatic and predicting in advance whether they will get HD --> cannot tell you when thou and how bad it will be


What other diseases can predictive testing be used on?

BRCA (familial breast cancer genes)
HNPCC (Hereditary non-polyposis colon cancer)
Myotonic dystrophy


What is the aim of predictive testing in terms of treatment of HD?

Hope that early identification leads to reduced morbidity and mortality through targeted screening, surveillance and prevention


What are the treatments of HD?

Symptomatic treatment only at present

No prevention or cure

Testing does not save lives


What are reasons for testing for HD?

Just ‘want to know’
Plan future care
Want to plan their career
Make decisions about children
Inform other relatives whose risk may change


What is the chance of a child having HD if one of there parents have it?



Can a embryo be tested for HD?

Yes a genetic test of the embryo can be done and the ones with the HD mutation can be discarded


What is the limitations of predictive testing?

While if positive is certanity of full penetrance it does not tell you how bad it will be, when will it happen and the course.


What do you need to consider in Hd predictive testing?

Changing risk to others  children can all of a sudden become more at risk

Impact on current relationships – and future..

Psychological impact

No medical advances yet