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Remember from the first module that you can think of a typical brain as being like a car factory.

Inside the factory are robots that are responsible for manufacturing cars. You can think of these as proteins in our brains.

These robots in turn are built from blueprints that contain instructions on how to assemble them correctly. You can think of these as genes in our brains.

Click here to go back to module one if you would like to revisit these concepts. If not, scroll down to learn more!

This module will give a brief overview of our understanding on how genetics contribute to ASD.

We know there are many different robots involved in the assembly of a car, and that each robot contributes a different way.

In some car factories, there are changes in some of the blueprints that describe how to build these robots.

These differences affect the functioning of the robots and can result in the production of atypical cars..

These atypical car factories are similar to the autistic brain where differences in genes can lead to atypical proteins and behaviours.

But genetic factors are not the only thing that play a role in autism... there are environmental factors involved as well. This means that the cause of ASD is multifactorial.

To understand the roles of genetic and environmental factors involved in autism, let’s leave the analogy of the car factory.

We will start by thinking of each individual’s chance of developing ASD as an empty cup.

The cup is going to be filled with balls which represent the two different types of factors that contribute to ASD: genetic and environmental factors.

Genetic factors are also referred to as genetic variants which are differences in genes that affect protein function. They can be inherited from the parents or appear spontaneously in the child.

Genetic variants that contribute to the chance of developing autism will be represented with blue balls, where the size of the balls will represent how strong a role that variant plays.

Some genetic variants play a stronger role towards developing autism

While other genetic variants play a weaker role.

Environmental factors that contribute to ASD will be represented by yellow balls.

We all start off with a chance to develop ASD,

but only individuals with enough genetic variants and environmental factors will develop the disorder.

The genetic basis of ASD is complex because each individual with the disorder will have a unique combination of genetic and environmental factors.

In addition to this level of complexity, these genetic variants can either be inherited from the parents

or appear spontaneously in the individual.

Now, let’s take a look at some examples of genetic variants that illustrate this.

For this individual with ASD..

...he inherited a strong genetic variant from the mother

and weaker genetic variants from both parents.

This individual has ASD due to the combination of inherited strong and weak genetic variants.

For this individual with ASD...

he inherited a weak genetic variant from the mother.

In addition to this, a stronger genetic variant spontaneously appeared in the individual.

This individual has ASD due to the presence of a weak genetic variant that was inherited and a stronger genetic variant that was not inherited.

For this individual with ASD

he inherited weak genetic variants from both parents.

In addition, weak genetic variants spontaneously appeared in the individual.

This individual has ASD due to the combination of inherited and new weak genetic variants.

As you can see, each individual with ASD will always have genetic variants contributing to the disorder.

Genetic variants always play a stronger role than environmental influences in ASD.

Having only environmental factors would not be enough to fill the cup.

However, if the individual only has a single genetic variant contributing to ASD...

...it would not be enough to fill the cup and they would not have ASD

This is the reason why genetic variants don’t cause ASD, but only contribute to the chance of developing ASD.

There is no single gene that causes autism. Instead, there are many genes involved and it is incredibly complex.