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4.2 developmental 2 > autism - genes and environment > Flashcards

autism - genes and environment Flashcards

1
Q

evidence for genes and ASD (3)

A

higher co-occurrence of ASD in MZ than DZ twins

first degree relatives have increased behavioural/cognitive features associated with ASD
–> the Broader Autism Phenotype

ASD co-occurs with genetic conditions
–> e.g. 16p11.2 and Sotos Syndrome

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2
Q

autism twin study + results

A

first twin study in 1977

Hallmayer et al (2011) found:

  • 77% concordance in MZ
  • 31% concordance in DZ

suggests genetic link - but don’t know what it is

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3
Q

autism as a spectrum

A

wide spread of data along an autism questionnaire - difference between diagnosed and undiagnosed

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4
Q

the broad autism phenotype

A

behavioural features of ASD (social interaction, friendships, pragmatics and speech) investigated in parents of:

  • multi-incidence of autism families (MIAF)
  • single-incidence of autism families (SIAF)
  • families with children with Down’s syndrome

MIAF and SIAF parents showed increase in ASD related features

provides evidence for broad autism phenotype and genetic evidence for a genetic origin

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5
Q

sotos syndrome - characteristics and info

A

overgrowth syndrome
prevalence = 1/14,000

deletion on chromosome 5 - NSD1 gene

diagnostic criteria:

  • overgrowth with advance bone age
  • macrocephaly (large head circumference)
  • characteristic facial appearance
  • intellectual disability
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6
Q

sotos syndrome - study with autism

A

78 individuals with sotos syndrome

measured traits of autism using social responsiveness scale

83% scored above clinical cut off for ASD (had autism)

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7
Q

ASD co-occurrence with genetic conditions

A

e.g. sotos syndrome, fragile X syndrome, 16p11.2

supports idea of genetic association to ASD

some genes are more linked with ASD symptoms than others

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8
Q

complex genetics

A
  • large number of genes - most likely interactions between them too
  • ~65 genes linked to ASD - most likely involved in brain development
  • single cause not known (and unlikely)
  • but only 10-20% of ASD cases are accounted for by known genetic abnormality
  • could it be that genes predispose and then there’s an external trigger
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9
Q

environmental epidemiology

A

observation of human populations infer the environmental causes of a condition or disease

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10
Q

bad scientific research with ASD - MMR vaccine

A

1998 - Wakefield et al - claimed link between MMR vaccine and autism

  • only small sample of 12 children
  • media repercussions - people choosing to not vaccinate kids - therefore more measles globally
  • lack of trust around research on environmental causes of autism
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11
Q

MMR and autism - corrective study

A

paper was retracted due to evidence that parts were fraudulent

follow up studies have found no evidence for MMR vaccine and autism link (2019 study of 650,000 children)

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12
Q

environmental factors linked to autism (8)

A
  • prenatal viral infection e.g. influenza, rubella ( depends on immune status of mother)
  • maternal diabetes
  • maternal obesity
  • prenatal stress
  • teratogens e.g. valproic acid (for epilepsy) or psychoactive drugs
  • pesticide exposure in first 8 weeks of pregnancy
  • parental age - advanced maternal age
  • air pollution

NO CONCLUSIVE FACTORS KNOWN YET

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13
Q

issues with environment and autism

A

tricky to identify causes

using correlations - not causation

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14
Q

how to establish causality with environmental epidemiology - Hills criteria (9)

A
  • temporality = effect after the cause
  • consistency = similar findings in other contexts
  • strength = of relationship between variables
  • analogy = other similar relationships
  • plausibility
  • experiment = well designed and conducted observation
  • biological gradient = greater exposure = greater incidence
  • specificity = effect only found in relation to cause OR there is only one effect associated with the cause
  • coherence = do findings match lab studies or well established relationships
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15
Q

environmental epidemiology research limitations

A
  • observational research - not fully controlled
  • records extraneous variables too
  • results of one study are easily challenged
  • confidence in results - meta-analysis used to make this stronger and see if relationships remain

example of contradiction:

suren et al (2013) - 85,176 children - folic acid during pregnancy reduced risk of autism

virk et al (2016) - 38,035 mothers - no evidence that folic acid reduces autism risk

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16
Q

air pollution and autism - meta-analysis

A

lam et al (2016)

screened set of papers with key words of autism and air pollution - fit inclusion criteria - reduced from 1,155 papers down to 23 suitable

exclusion = no original data, no human subjects, diagnosis of autism or definition of air pollution that wasn’t in line with PECO definition, no comparator group

particulate matter = small particles, used to mean air pollution

found small but significant association between particulate matter and ASD

17
Q

odds ratios

A

odds ratio (OR)

statistical understanding of association between exposure and an outcome e.g. likelihood that cigarette smoking causes lung cancer

OR = 1 = exposure does NOT lead to an effect
OR < 1 = greater exposure is associated with less of an effect
OR > 1 = greater exposure is associated with larger effect

18
Q

odds ratios showing risk of ASD from MMR vaccine

A

all datasets showed OR of <1 (all around 0.9)

therefore no association between MMR and ASD

19
Q

conclusion: do environmental factors cause ASD

A

difficult to measure environmental exposure accurately

little evidence for environmental causes

possible suggestion to focus on particulate matter (pollution) as a risk factor

however - generally weak evidence for direct causal link between environment and ASD

20
Q

gene-environment interaction in ASD

A

e.g. air pollution and MET gene

air pollution correlation with autism risk

MET gene (codes for proteins that trigger mitogenesis [cell division] and morphogenesis [ structural development] associated with autism risk

animal models - air pollution directly effects MET expression

shows 3 way link between gene, environment, and autism

21
Q

ASD, MET, air pollution - study

A

Volk et al (2014)

  • 252 autistic children + 156 neurotypical controls from Californian preschools
  • MET genotype assessed via blood test
  • exposure to air pollution measured for each

results:
interaction effect - children with both an alteration to MET gene and increased exposure to air pollution = increased risk of autism than those with just MET alteration or just increased air pollution exposure

therefore there is an interaction between genes and environment found

4.2 developmental 2 (11 decks)

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