These influences appear to increase the risk that a child will develop autism. However, it’s important to keep in mind that increased risk is not the same as cause. For example, some gene changes associated with autism can also be found in people who don’t have the disorder. Similarly, not everyone exposed to an environmental risk factor for autism will develop the disorder. In fact, most will not.
Genetic Risk Factors
Research tells us that autism tends to run in families. Changes in certain genes increase the risk that a child will develop autism. If a parent carries one or more of these gene changes, they may get passed to a child (even if the parent does not have autism). Other times, these genetic changes arise spontaneously in an early embryo or the sperm and/or egg that combine to create the embryo. Again, the majority of these gene changes do not cause autism by themselves. They simply increase risk for the disorder.
Environmental Risk Factors
Research also shows that certain environmental influences may further increase – or reduce – autism risk in people who are genetically predisposed to the disorder. Importantly, the increase or decrease in risk appears to be small for any one of these risk factors:
No effect on risk
Differences in Brain Biology
How do these genetic and nongenetic influences give rise to autism? Most appear to affect crucial aspects of early brain development. Some appear to affect how brain nerve cells, or neurons, communicate with each other. Others appear to affect how entire regions of the brain communicate with each other. Research continues to explore these differences with an eye to developing treatments and supports that can improve quality of life.