Causes of autism (spoiler alert, not vaccines)

I have been doing some research into the possible causes of autism out of curiosity, but I decided to summarise the papers that I have found so far in a post. I will talk about some possible causes as well as things that are definitely not causes, based on credible studies I have found (*cough* not Wakefield *cough*). I want to preface this by saying that I am not doing this to look for ways to prevent autism in people; I do not see autism as something we should try to avoid. I am trying to approach this from the perspective of the scientist that I am; and I am simply presenting the evidence I have found to educate others. Any research or websites I mention will be linked at the bottom of this post.

Things that do not cause autism

The first thing that I want to get out of the way is that I have found absolutely no evidence that vaccines of any kind can increase the chance of someone being autistic.

The NHS website lists various factors which have no links to autism prevalence based on current research, including:

  • Vaccines
  • Parenting style
  • Diet
  • Illness or infection

With the controversy around Andrew Wakefield’s work on the MMR vaccine still affecting opinions on vaccination and the current discussions around COVID-19 vaccines, I wanted to look a little further into research around vaccines specifically. I found a review article by Doja and Roberts (2014) that summarised a huge number of studies focusing on links between the MMR vaccine and autism, and they concluded that there was no correlation.

Obviously the misinformation around vaccines and autism is extremely harmful and is one of my motivators for doing this post. Regardless, I want to make one thing very clear. Even if there is a tiny chance that vaccines could be linked to autism, I would rather be autistic than dead.

Actual possible causes of autism

Now that I have addressed vaccines, I will explain some research which investigated factors which may actually be linked to autism. This part of my research was really interesting, and I hope I do it justice by explaining it clearly.

Genetic causes – one gene or multiple?

I found multiple sources which mentioned the heritability of autism, suggesting that genetic factors are involved (including the NHS website, Ambitious about Autism, the National Autistic Society). However, these websites did not go into any sort of detail about what genes are involved.

When I dived into scientific papers, I found a literature review by Freitag (2006) which proposed the idea that multiple genes may be involved rather than a single genetic mutation. This was also the first paper that mentioned the huge spectrum of ways in which autism presents, and how this should be considered when looking for causes.

The Fractionable Autism Triad

The idea that multiple factors may be involved was also mentioned in a paper by Happé, Ronald and Plomin (2006). They examined the triad of traits used for autism diagnoses;

  • Impaired social interaction
  • Impaired communication
  • Restricted/repetitive interests or activities

They examined this triad across the general population and found that many people only exhibited difficulties in one of these areas. They also discussed the genes linked to each of these traits and found little to no overlap, suggesting that the causes for each of the triad are distinct. The developmental pathways related to each of these traits are very different as well, suggesting that cognitive and neural pathways may also be distinct (this is where the phrase “fractionable” appears). The authors concluded that there may be genetic, cognitive or neural causes linked to each of the triad individually.

Happé and Ronald followed this paper with another in 2008 which started to investigate possible causes for each of the triad. This included the phrase “the heterogeneity of etiology” which explains instances where different causes can lead to the same condition. This study observed families with a mix of autistic and neurotypical members, as well as sets of twins. This study revealed that autistic traits are very heritable individually, but that only monozygotic (identical) twins had a significantly increased chance of exhibiting the exact same traits as their autistic twin. This study suggested that the triad are often displayed very differently, even in members of the same family.

What does this mean for autism diagnoses?

The research I have found so far points to a reexamination of how the triad is used in formal autism diagnoses. We need to recognise that most people do not exhibit all of these traits, and look further into how this may be preventing people from getting the diagnosis that they need. The traits may also be linked to developmental cognitive or neural pathways, but this needs more in-depth research.

This can be extended to research focusing on specifically female (AFAB) autistic individuals, to ensure that the triad is just as accurate for everyone. This is something I am particularly passionate about and I hope that future research examines this further.

There is more to be done

In summary, there is still a long way to go before we discover the exact causes of autism, but I hope that this post can act as a short summary of what we currently know, and that I can also help to dissipate any doubts around autism and vaccines.

I hope this post was informative and if you have any questions, I’m happy to try and help! I’m still learning about autism and I am also very eager to talk with people who have done further research and want to discuss it!

References

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