What twins can teach us about the causes of Autism

In my first post of this series, I made the case that vaccines do not cause autism. If it isn’t vaccines though, what exactly is causing Autism?

We’ve established that Autism is a condition in which the brain processes emotional and social information differently than normal brains. The question is what is causing the brain to get wired in this different way? Autism Spectrum Disorder presents in early childhood, which also happens to be the age when the brain is going through one of the biggest developmental changes. This suggests that something is happening in these young brains that changes the way they develop and therefore changes how they process information. But what?

This is still an open question, and scientists are working hard to nail down what the causes of Autism are. Which is why it is such a tragedy that so much money, time and resources are getting diverted into studies double-checking (now triple- or quadruple-checking)  that vaccines are not the cause. But just because this is an open question doesn’t mean we have no idea what causes Autism. Recent studies have shown strong evidence that there are genetic and environmental factors that increase a child’s likelihood of developing an Autism Spectrum Disorder.


Scientists have not discovered an “autism” gene. There are some diseases that can be tracked down to a single gene causing the entire disease, but usually things are lot more complicated than that when it comes to genes and diseases. Autism is in the category of “genes are involved, but it’s complicated.” If we can’t find a gene that causes Autism Spectrum Disorder, then how do we know genes play a role at all? The answer is twin studies! Twin studies are an amazing tool when trying to find out if a disease is caused by genes or not. What these studies do is compare the rates of the disease, in this case Autism Spectrum Disorder, in identical twins and in fraternal twins. Identical twins have the exact same DNA as each other, but fraternal twins share the same amount of DNA as normal siblings. This is a very powerful analysis because both kinds of twins share the same womb and are likely exposed to roughly the same environment as their counterpart. So if you find higher rates with identical twins – meaning if one identical twin has Autism then the other has a very high chance of having it too – but not in fraternal twins, then you can bet that there is a gene or group of genes that are behind the disease. Next time you see some twins, be sure to thank them and their kind for their help in figuring out if diseases are caused by genes!

This is exactly what the Autism twin studies are finding. If you take an identical twin who is diagnosed with an Autism Spectrum Disorder, there is a very, very high chance that the other twin has it too. But if you take a fraternal twin who has Autism, the other twin only has about one in three chance of also having it. What does this mean? Since the fraternal twins only share about half their genes, the other twin may or may not receive the genes that are causing Autism. With identical twins on the other hand, since they have exactly the same DNA if one of them has the Autism genes the other is guaranteed to have them too.

The next step is to examine very closely which genes people with Autism have in common with each other and what those genes do in the body that leads to the disorder. In that regard, there is still a lot of work to do, but progress is being made. For example, a recent study released by the Psychiatric Genomics Consortium found some genes that were likely culprits in Autism Spectrum Disorder. When they examined what these genes are for, they found they are needed by your brain to make calcium-channels. I don’t want to stray too far off topic, so I won’t go into detail on what calcium-channels are. But they are little proteins found all over the brain that are critical tools to allow you neurons to talk to each other. In other words, having different or broken calcium-channels would almost certainly change how your neurons can communicate with each other and therefore how your brain processes information. Another really interesting finding from this study was that these genes that might cause autism are also commonly found in other developmental brain disorders like Schizophrenia, Attention Deficit Hyperactive Disorder, and even depression.

These studies tell us that Autism Spectrum Disorder has a big genetic link, but you’ll notice that twins with identical DNA did not both have Autism 100% of the time. The chances are very high, but not guaranteed. If Autism is genetic and they have the same DNA then how could one twin get Autism but not the other? The answer seems to be that environmental factors play an important role in Autism Spectrum Disorders too. 


Scientists often talk about how “environmental factors” influence or cause some disease or disorder. That can be a little confusing because they are usually not talking about the environment as in blue skies and clean oceans. They mean environment as in the things outside of the body that came into contact with the body. That means the chemicals inside the mother’s womb, the diet a baby was fed, or the materials inside the baby’s house are all considered “environmental” factors.

A lot of research is being conducted to look at which environmental factors might be increasing the chances of getting Autism, and importantly which factors might protect developing children from the disorder. One study found that if a mother caught the flu while she was pregnant the baby was twice as likely to develop an Autism Spectrum Disorder, and if the virus caused a long fever the baby was three times as likely to have Autism. As an aside, if you know people who worry that vaccines cause Autism, you can tell them not only are vaccines not the cause but in fact they might reduce Autism rates when pregnant mothers get the influenza vaccine (the CDC says the influenza vaccine is safe for pregnant woman). Be sure to leave a comment describing how that interaction goes!

As an example of environmental factors that reduce the risk of Autism, one study looked at the rates of Autism in mothers who said they did or did not take prenatal vitamins. They found evidence that women who took prenatal vitamins before pregnancy and during the first month of being pregnant were less likely to have children diagnosed with an Autism Spectrum Disorder.

What does this all mean? There are probably lots of different genes that can lead to a developmental problem that causes an Autism Spectrum Disorder. In some cases the child might have several genes that lead to Autism, and therefore they get the disorder no matter what happens. In other cases children might have some of the Autism-genes but not others. In these cases, maybe the interaction of those genes with their environment during pregnancy and early childhood determines if and how severe their Autism will be. But the bottom line is we need to do a lot more research to work out this puzzle better.

To get there faster, we need to stop throwing away precious research dollars at studies designed to convince a nervous public that vaccines are not the culprit.

Politicus Cerebri


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s