Real science has shown us that vaccines are unrelated to autism. Over a hundred peer-reviewed published studies refute the hypothesis that vaccines are linked to autism spectrum disorders (ASD). And despite the pseudoscience pushed by vaccine deniers, the scientific consensus is that vaccines do not cause autism. So, what causes autism? That’s a question that has not been completely answered, but we have a lot of evidence supporting a few hypotheses.
There have been a whole bunch of proposed causes for autism, other than vaccines. GMOs. Pesticides. Emily Willingham, Ph.D., whom I consider to be one of the leading ASD scientific experts on this planet, wrote a hysterical, but still appropriate, article about all the popular “causes” of autism:
This last week or so, every day seemed to bring a new finding about something linked to autism. I blogged one of them — diabetes — but who really would have the wherewithal to follow the growing list of factors linked to autism? I guess I would because below, I give you that very list, including current pop hits and some blasts from the past, with some brief commentary. Without further ado — The ever-changing face of autism — or, as some have wisely suggested we call it — the autisms.
What causes autism is a question that does not have “vaccines” as the answer. And despite all of the memes, Facebook groups, and nonsense pushed by pseudoscience websites, like Age of Autism, science actually has a pretty good idea about what causes autism. And let me repeat it once more, it isn’t vaccines.
What is autism spectrum disorder
I’m not going to go into all the details about ASD diagnosis, symptoms, and treatments – that would take up a book. But, I will spend a bit of time defining what constitutes autism spectrum disorder. ASD is a range of different conditions classified as neurodevelopmental disorders in DSM-5. However, individuals diagnosed with ASD must present with two general symptoms:
- Deficits in social interaction and communication
- Repetitive and restricted patterns of behavior interests or activities
Autism spectrum disorder encompasses diagnoses of autism, Asperger syndrome, pervasive developmental disorder not otherwise specified (PDD-NOS), and childhood disintegrative disorder. All of these disorders include the following features – social deficits, communications difficulties, repetitive behaviors and interests, sensory issues, and, occasionally, cognitive delays.
Furthermore, there is a range of symptoms from minor to severe, with each person with ASD expressing it in an almost infinite variety of symptoms and severity. Although ASD is considered “incurable,” it is not a sentence of a mental prison for the patient. The lay public tends to box ASD children into one small stereotype, as people do with most mental health disorders, despite the fact that there is huge variability in how a child expresses ASD.
There is a variety of evidence-based interventions for autistic children. Many of the methods employ a psychoeducational approach to enhance cognitive, communication, behavioral, and social skills. There is no single treatment that is best for all children with ASD, so treatment is typically adjusted to meet the needs of the child.
Although evidence-based interventions for autistic children vary in their methods, many adopt a psychoeducational approach to enhancing cognitive, communication, and social skills while minimizing problem behaviors. It has been argued that no single treatment is best and treatment is typically tailored to the child’s needs.
I think the most important thing to note about ASD is that it is a complex disorder with a wide range of symptoms. It’s not a “death sentence” for either the parents or child, despite what you may have heard on the internet.
What causes autism – genetics
The best evidence we have is that ASD is a genetic disorder. Researchers first recognized genetics as the foundation of ASD in the 1970s. Studies on twins showed that monozygotic twins (genetically identical) were more likely to share a diagnosis of ASD than dizygotic (non-identical) twins. That is a strong indicator of a genetic relationship to ASD.
More recently, a large population study, which included over 7,000 pairs of twins, provided further evidence of a genetic link for ASD. The authors concluded that,
Genetic factors underpinning individual differences in autism like traits show considerable overlap with genetic influences on diagnosed ASD.
Studies have consistently found that the prevalence of autism in siblings of autistic children is approximately 15-30 times greater than the rate in the general population. Based on all of this supporting evidence, researchers have come to deduce that shared genetic variants in families are probably more important than shared environments for triggering ASD in children.
Actually, there have been over 100 genes that have been identified to be linked to ASD. That’s more linked to genetics than other common health problems that are known to have links to genetics like cardiovascular diseases or some cancers.
The big question that remains is how do these genes affect the brain that leads to ASD. Research is moving to examine those gene mutations that increase (or decrease) the risk of developing ASD.
I know that there is a tendency to want to blame something for ASD. It’s a hard realization that ASD is related to one’s genes that they pass on to their children. But there’s no blame there – it’s how genes randomly combine to form your child.
What causes autism – exposure to infections and medications during pregnancy
Let’s be clear – not everyone with the genes discussed above has ASD. Because mutations to genes alone may not be solely responsible for ASD. Once a child has an underlying genetic predisposition or mutation to ASD, it may take a trigger from an environmental factor to fully cause ASD.
This is where the science starts to get a little hazy – there are tons of different potential environmental factors that might contribute to or trigger autism. And no, vaccines are not one of them, that’s been dismissed by scientific evidence. But other contributors are still in the hypothesis stage – pollution, pesticides, anti-depressants, and viral infections. Unfortunately, as Dr. Willingham implied, there are a bunch of hypotheses that lack robust evidence to support them. In many cases, we have robust evidence that the hypothesis is completely wrong (did I mention vaccines?).
We have a lot of confidence that there is a genetic predisposition to autism. Very robust, repeated, and published evidence. On the environmental side, there is little clarity (except that vaccines are not related – am I repeating myself?).
So what do we have? There is very strong evidence that a rubella infection during pregnancy leads to a significantly increased risk of autism in her baby. Immunization against rubella before or during may be an effective strategy to reduce the risk of autism in children of those mothers.
The evidence of a relationship between other viruses and autism is not quite as strong. For example, there is some very weak evidence (reviewed here) that influenza in pregnant mothers may be related to an increased risk of autism in their children. Since the flu vaccine is very safe for use in pregnant mothers, it is a good argument to get the vaccine.
Despite what you’ve read on the internet, most of the other evidence is weak, conflicting, or downright inconclusive. For example, what about SSRI antidepressants? Actually, a meta-review of anti-depressant use during pregnancy showed no effect on the risk of ASD in babies as a result of antidepressant use by the mother. However, it is possible that depression (not the use of antidepressants) in the mother prior to conception may be an environmental risk factor.
A massive meta-review of environmental risk factors showed either a small correlation to ASD. Or none at all. Here are some of the factors where there is no robust evidence that there is either a positive or negative association between it and ASD:
- Preconception chemical exposure
- Pesticide exposure during pregnancy
- Pesticide exposure during childhood
- Air pollution
- Heavy metals (including mercury, lead, cadmium, aluminum, arsenic, nickel, uranium, and tin)
- Urine porphyrin
- Folic acid
- Camel milk (yes, camel milk)
- Gluten free diet
In fact, the review found only one environmental risk factor that has a strong association with ASD – valproate, a medication used to treat epilepsy and bipolar disorder.
Another environmental factor seems to be strongly linked to ASD – being male. According to research, autism spectrum disorder affects boys about 4X more than girls. It also appears that it takes fewer genetic mutations for boys to get autism than girls. The reason for this male risk factor is unknown, though there’s a lot of wild speculation, including that there might not be sex-based differences in risk, it’s just harder to diagnose in girls.
What causes autism? Still not vaccines
After reviewing the evidence, we know two things for sure:
- Vaccines are not related to autism.
- Genetics are related to autism.
Other than those two scientifically supported conclusions, research is still ongoing and is mostly inconclusive. So why do some parents still want to blame vaccines? There are probably a lot of reasons, but mostly it’s because they ignore the ironclad conclusive evidence about vaccines and ASD, and focus on the general lack of strong evidence in other areas.
The evidence about autism and genetics is complicated and not prone to a simplistic, one-sentence description. It’s easy to wrap your arms around it like “vaccines cause autism” – it’s simple and easy to state. On the other hand, there’s the little issue that if your child has autism and that’s a result of genes, those genes come from only two places – the mother and father. Maybe it’s just easier to blame vaccines or gluten in the diet rather than accept that one’s own genes are to blame.
There is a boatload of research that needs to be done for us to completely understand what causes autism spectrum disorders. But we have a boatload of evidence that it’s not vaccines.
- Atladóttir HÓ, Henriksen TB, Schendel DE, Parner ET. Autism after infection, febrile episodes, and antibiotic use during pregnancy: an exploratory study. Pediatrics. 2012 Dec;130(6):e1447-54. doi: 10.1542/peds.2012-1107. Epub 2012 Nov 12. PubMed PMID: 23147969.
- Brugha TS, McManus S, Bankart J, Scott F, Purdon S, Smith J, Bebbington P, Jenkins R, Meltzer H. Epidemiology of autism spectrum disorders in adults in the community in England. Arch Gen Psychiatry. 2011 May;68(5):459-65. doi: 10.1001/archgenpsychiatry.2011.38. PubMed PMID: 21536975.