Week 10: Autism course Flashcards
Prevalence of Autism
Prevalence of autism is 1 to 1.5%
Prevalence has increased over time
Could be an actual increase in number of children who have autism vs.
Or a better identification and broader definitions
Cultural and contextual differences
Present cross-culturally and cross-nationally
Found at all income levels
Gender differences
4: 1 male to female ratio
10: 1 male to female ratio in “high functioning” ASD
Development Course of Autism
Most often identified by parents in the months preceding child’s second
birthday
Diagnoses may around 2 to 3 years are generally stable
Some children display symptoms since birth
Some children seem to lose early developmental milestones
Efforts to create very early ID tests because early treatment yeilds better results
For example:
(1) using eye tracking to see what toddlers are looking at
-Toddlers with autism focus on geometric rather than social images
(2) Brain enlargement
-Recent data indicate that rate of cortical surface expansion between 6 and
12 months predicts diagnosis of autism at 24 months (Hazlett et al. 2017)
Usually lifelong
Variability in trajectories of children with ASD
Strongest predictors of adult outcomes
- Language
- IQ
Comorbidity
Intellectual disability
- 70% of youth with autism meet criteria for ID
- 40% meet criteria for severe or profound ID
25% have “splinter skills” - special talents above that which you would expect given the child’s usual abilities or what you would expect from the general population
5% display isolated and remarkable talents - really exceptional
Differentiating autism from ID
Children with ID have
- No specific deficit in joint attention
- No specific deficit in theory of mind
- No specific deficit in pretend play
- Social behaviors appropriate for their mental age (even if lower than their chronological age)
Other comorbid conditions
- Epilepsy
- ADHD, conduct problems, anxiety disorders, depression
Etiology of Autism
- Environmental factors
- Genetic factors
- Brain development
Etiology of Autism: Environmental Factors
Toxin hypotheses
Gluten-based diet (cereal)
Casein-based diet (milk)
Increase in number of vaccinations children receive
1900 – 1 – Small pox
1960 – 5 – Add diphtheria, tetanus, pertussis, polio
1980 – 8 – no small pox, add MMR (measles, mumps, rubella)
2000 – 11 – includes hepatitis, meningitis
Current vaccination schedule in Quebec
14 separate shots by 6 years of age
Includes pneumonia, flu, rotavirus, chickenpox
Vaccinations and autism
Thimerosal
-Preservative in vaccines
-Removed from nearly all vaccines in 2001 (e.g., some flu vaccines, not given
to children)
-Mercury
-Symptoms of autism are noticed right around the time children get their
vaccinations
-Increased use of MMR vaccine appeared to coincide with increased
prevalence of autism (although in California and Denmark, increase in
autism happened well after the introduction of the MMR vaccine)
-Reasonable biological explanation
Wakefield the asshat and the MMR
Wakefield et al. 1998
-12 children
-Normal development followed by onset of behavioral difficulties and
gastrointestinal problems
-For 8 children, onset was linked to MMR vaccine by parents or physician
-Note that the authors were careful to point out that this study did not
prove a link between behavioral problems and vaccination
-Also noted that only a subset of autistic cases linked to vaccine
After publication, MMR vaccine rates dropped
In UK
-1996 – 92%
-2006 – 85% (compared to 94% for other vaccines)
2006 incidence rates for measles and mumps were 13 and 37x times higher than in 1997
Subsequent research evidence
-12 epidemiological studies have found no link between the MMR (measles/mumps/rubella) vaccine and autism
-Largest: All children born in Denmark between January 1991 and December
1998 (N = 537, 303)
-Compared children who had received MMR vaccine (440,655) and children who
had not received MMR vaccine (96, 648)
-Children in the vaccinated group did not have greater risk of developing autism
compared to the unvaccinated group
-There was also no association between age of vaccination and autism
-6 studies have found no evidence of a link between thimerosal and autism
-3 studies have found no evidence that thimerosal is associated with more
minor neurological difficulties
De Stefano et al. 2013, Journal of Pediatrics
-Examined association between level of immunological stimulation in
first two years of life and development of autism
-Found no association
-Greater number of vaccines not associated with autism
Anti-vaccination group funded a study involving randomly assigning
monkeys to receive different types of vaccines
Not ethical to assign babies to a 1990s vaccine schedule
Gadad et al. (2015) in Proceedings of the National Academy of Sciences
- 79 rhesus macaques randomly assigned to receive:
- 1990s pediatric vaccination schedule
- 1990s pediatric vaccination schedule but four times faster (because monkeys develop faster)
- 2008 expanded pediatric vaccination schedule
- Only thimerosal containing vaccines
- Only the MMR vaccine
- Control - saline
Gadad et al. (2015)
-Vaccinations were not associated with any behavioral changes
-E.g., stereotyped behavior, fear-disturbed behavior, positive social
behaviors, non-social exploring behaviors
-Vaccinations not associated with any neuropathological changes in the cerebellum, hippocampus, and amygdala
Its all balls
Scientific inference and Vaccine Skepticism
Null hypothesis: Assume no relationship
-Using probability theory, determine how likely the observed relationship is if there is really no relationship
-Could we expect to observe this association by chance?
-P < .05 means that there is less than a 5% chance that we would observe an association this big if, in reality, there was really no
relationship
-It does not mean that there is a 5% chance that there is no relationship
We do not quantify the likelihood of no relationship
-We cannot “prove” the null hypothesis
This leads to people interpreting this as unproven
Lancet retracted the paper
In January 2011, reported in the British Medical Journal that the data reported were in fact fraudulent
Wakefield lost his medical license in the United Kingdom
Etiology of Autism: Heritability
15-20% of siblings of individuals with ASD have the disorder
- Concordance rates
- 70-90% in identical twins
- Heritability of an underlying liability for ASD is 90%
Etiology of Autism: Molecular
Genetics
-Points to particular areas on many different chromosomes as
possible locations for genes for ASD
-ASD is likely to be a complex genetic disorder
-Expression of ASD genes may be influenced by environmental factors occurring primarily during fetal brain development
What happens in utero affects this
