What is Downs syndrome?
- Most prevalent neurodevelopmental disorder
- Affects 1 in 800 to 1000 births
- Genetic condition with known aetiology
- Causes level of learning disability and characteristic features
Does DS have a genetic basis?
The aetiology of DS is known - chromosomal abnormality.
3rd chromosome 21 present from conception = genetic trisomy
c.21 contains approx. 1% of body's genes.
DS results from change in gene quantity NOT gene quality.
Inc. in maternal age = inc. in risk of DS (age 35 1:400 risk). No impact of paternal age.
No evidence that anything done before/ during pregnancy increases/ decreases risk.
3 types: trisomy 21, translocation, mosaicism
Majority of cases of DS are not inherited - only in translocation.
How is DS diagnosed?
Screening during pregnancy to determine likelihood of baby having DS.
- SCREENING - blood test and nuchal translucency ultrasound scan
- IN-WOMB - Chorionic Villus Sampling (sample of placenta) or amniocentresis (small sample of amniotic fluid). Both in-womb procedures increase risk of miscarriage.
- AFTER BIRTH - Based on characteristic physical appearance/ behaviours. Blood test to confirm extra chromosome 21.
What are the symptoms of DS?
- Physical appearance: reduced muscle tone (hypotonia), small nose and flat nasal bridge, small mouth with protruding tongue, upward slanting eyes, broad hands with short fingers, below average weight and length at birth
- Delayed development and learning difficulties, slower to learn skills
- Other health problems e.g. cardiovascular, respiratory, hyperacusis.
What is the cognitive profile of DS?
- IQ is moderately to severely delayed (25-55)
- Discrepancies in skill areas magnified over development
- Struggle with pretend and reality - unable to differentiate between the two
- Have difficulty combining behaviours and co-ordinating attention
- Dissociation of verbal and non-verbal skills.
Chapman & Hesketh (2003) - dissociation of verbal/
Found a dissociation between verbal and non-verbal skills.
Strengths = visual, social functioning, self-help and living skills
Limitations = impaired speech and language skills
Laws & Bishop (2003): DS and SLI
Compared verbal abilities/ language profiles of children with SLI and DS.
Found to have similar language profiles:
- Poorer expressive language than comprehension.
- Poor grammar.
Chapman et al (1998): language tests
Used formal language testing.
Conversational and narrative language samples from DS and controls matched for non-verbal mental age.
DS poorer in number of different words used, total number of words used and mean length of utterance (MLU). Poorer intelligibility.
:( Unequal sample sizes, how was MA measured - may not have been useful for both samples?
What is the social phenotype of DS?
Strength in area of social development. Display high overall social competency e.g. participation in groups, number of friends.
Zickler et al - DS infants show significantly more approach behaviours than TD infants.
Kasari et al (1990) - DS children more interested at looking at the experimenter's face than out-of-reach toy.
8-19 month infants with DS looked at caregivers for longer periods, and showed less joint attention than TD infants.
Kasari et al (1995) - Investigated extent that child engages with social referencing. Robot study - robot elicited emotional response from parent. TD child looked at robot twice as often as parent; child with DS showed equal looking.
- May be due to attentional deficits rather than ability to social reference.
Kasari et al (1990) - DS children showed more distress than controls to an experimenter who had pretended to hurt themself. = sensitive to distress cues, may understand emotions expressed.
What is the brain development of DS?
30% of individuals with DS are affected by dementia - prevalence may increase with age.
By age 35, individuals with DS develop neuropathic changes similar to those found in Alzheimers, signs of brain neuropathy, leading to loss of learning and memory abilities.
Difficult to test - recruitment issues, homogeneity of groups is difficult to ensure.
Volume reductions found in hippocampus, PFC and cerebellum (Weis, 1991):
- Hippocampus - memory and emotion
- PFC - planning behaviour, decision-making and social involvement
- Cerebellum - role in language and attention
Atypical brain development - abnormal by adulthood. Reduced brain development in 1st few months of life, fewer neurons developing.
FUTURE: gene therapy to silence the effects of the extra chromosome, may be possible in the future (BBC, 2013).
What is DS co-morbid with?
- Cardiovascular problems
- Mouth problems - soft palate, teeth, tongue
- Gross and fine motor difficulties
- Hyperacusis - sensitivity to loud noises
- Risk of feeding problems
- Respiratory problems
- Sleep apnea (45%)
- Mental health problems - ADHD, autism