Down Syndrome

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Author:
thayman1
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220979
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Down Syndrome
Updated:
2013-05-24 14:21:11
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L2
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Lecture 2
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  1. Genetic cause of DS
    • Trisomy on chromosome 21
    • Effects of trisomy vary from individual differences
    • There are around 300 genes on chromosome 21 but not sure which ones are implicated
    • Genetic but not hereditary in at least 97% of cases
  2. Mosaicism
    • in 2% of cases not all cells have trisomy on chromosome 21 (i.e. some cells underwent nondisjunction and revert back to normal)
    • leads to a milder version of DS
  3. Environmental cause of DS
    • Maternal age
    • RISK:
    • 1/1200 @ 25
    • 1/900 @ 30
    • 1/350 @ 35
    • 1/100 @ 40
    • 1/30 @ 45
  4. Why are Mouse Models useful?
    Useful for finding out how genetics influence brain development
  5. What do we learn from MM about DS?
    • There are abnormalities in dendritic structure and transmission in hippocampus (memory and learning)
    • problems with neural plasticity
    • smaller cerebellum
    • leads to problems with motor skill, learning and cognition
  6. How can neuroscience inform treatment?
    • imbalance between excitatory and inhibitory neurotransmission can be restored using drugs(successful in ability to learn with mice)
    • growth factor has a role in the development of the cerebellum therefore agonists (which activate receptors) can restore cerebellum function to normal with positive neural effects
    • not a cure but function better with drugs
    • interested in the timing of administering drugs
    • can the drugs actually change the developmental trajectory (i.e. can changing the size of the brain early enough will they learn enough to kick start other neural systems?)
  7. Physical features of DS
    • eyes slant upwards
    • protruding tongue (articulation difficulties)
    • loose joints
    • shorter stocky stature
  8. Intellectually impaired
    • IQ 40-70
    • early AD
    • motor delays which can impact on cognitive development
  9. Associated deficits
    • co-morbidity with ASD (5-10% meet criteria)
    • behavioural problems
    • BUT very social
  10. MANTRY et al 2008 aims
    • investigate mental health issues in a DS population rather than a clinical group
    • are people with DS at a greater risk of developing mental health issues compared to people with general intellectual difficulties?
  11. MANTRY et al 2008 results
    • rates of mental health issues are low
    • higher rates of AD and depression (but still relatively low)
    • the more intellectually impaired/ language impaired were not more prone to these difficulties environmental factors such as caring home environment did not have any bearing on later mental health
  12. MANTRY et al 2008 conclusion
    • rates overall are low and are not associated with any environmental factors
    • there must be biological factors that influence mental ill health
    • whatever the biology of DS is it is quite protective against other mental illnesses
  13. MANTRY et al 2008 criticism
    • population study avoids berkson's bias
    • no control over environment (e.g. life events)
    • challenges to gaining consent
    • do these people even know they had these mental illnesses (ethical issues)
    • more severe people don't take part
    • need lots of participants
  14. Prevalence and Incidence:
    • how people with DS at this point in time have a mental illness
    • the number of new cases reported over a specified period of time
  15. FIDLER & DAUNHAUER 2011 intellectual impairment and trajectory
    • develop at the same rate as peers (thought still behind)
    • then there is a plateau of cognitive ability with very little change
    • in 30s and 40s there is a decline = early onset AD (marked by changes in behaviour rather than memory loss
  16. FIDLER & DAUNHAUER 2011 slow processing speed
    takes longer to orient/respond to environmental stimuli (particularly language)
  17. FIDLER & DAUNHAUER 2011 Executive function deficits
    • have particular problems with inhibition, set shifting and planning (linked to verbal ability)
    • Executive control is very much linked to language
  18. NAESS et al 2011
    • variability in language profiles across difference domains
    • profile mirrors SLI
    • problems with speech production (articulation) due to global motor deficits
    • have late onset of their first words, DD children do take longer to get started
    • understanding is better than what they can produce (very typical in development)
  19. NAESS et al 2011 vocabulary
    • vocabulary is much better than aspects of grammar it’s at the level you would expect for their chronological age = better than you would expect for mental age
    • expressive language predicted by CA and MA = worse than understanding
    • ability to string sentences together in a coherent discourse is predicted by MA or by grammar comprehension (most impaired skill of all)
  20. Memory
    • uneven profile in memory ability
    • verbal memory is poor but strengths in visuo-spatial memory
    • have problems with phonological loop (remembering speech sequences and active rehearsal)
    • not related to speech deficits but may be related to deficits in spontaneous rehearsal (i.e. trying to say a phone number over and over to remember it)
    • they just don’t use it
  21. HULME et al 2012
    • Reading development
    • longitudinal design tells you about the magnitude of disorder and the rate of change
  22. HULME et al 2012 procedure
    • compared children with DS and children with typical development (TD) at three points in time on measures of reading, phonological skill and oral language (esp vocabulary)
    • phonological skills hugely predictive of reading skill but becomes less important over time and oral language takes over
  23. HULME et al 2012 results
    • time 1: groups were matched in word reading ability (non-words, words and letter sounds)
    • DS children worse on measures of language and phonology at all time points
    • TD made gains but DS reading ability remained relatively stable (not as much of a gain as TD)
    • DS non-word reading was worse given their word reading ability (a different path to reading?)
    • vocab not phonological awareness related to word reading ability which suggests a dyslexic type impairment in the mapping of sounds to letters

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