Is autism largely caused by genetics and not environmental factors, like vaccines?

accreditation
Is autism inherited?
Is autism inherited?

The largest study of its kind, involving more than two million people across five countries, finds that autism spectrum disorders are 80% reliant on inherited genes.

That means that environmental causes are responsible for just 20% of the risk.

Maternal factors not significant

The findings could open new doors to research into the genetic causes of autism, which the US Centers for Disease Control and Prevention now says affects one in every 59 US children.

It might also help ease fears that autism is caused by maternal factors – a mother's weight, mode or timing of delivery, or nutrient intake, for example. The new study found the role of maternal factors to be "nonexistent or minimal".

Instead, "the current study results provide the strongest evidence to our knowledge to date that the majority of risk for autism spectrum disorders is from genetic factors," said a team led by Sven Sandin, an epidemiological researcher at the Karolinska Institute in Stockholm, Sweden.

The new study might help dampen public interest in supposed – but unproven – "environmental" causes of autism, such as vaccines. Long-discredited, fraudulent data linking childhood vaccination with autism is still widely cited by the "anti-vaxxer" movement.

"The contribution of the environment to autism spectrum disorder risk appears to be much smaller than the contribution of genetics," a team of experts said in an editorial comment on the new study, which was published in the journal JAMA Psychiatry.

Largest and most rigorous study

However, genetic factors are frequently ignored, and instead environmental factors "often receive disproportionate attention from the public and the media, even when (as in the case of vaccine fears), they are debunked," wrote psychiatrists Drs Amandeep Jutla, Hannah Reed and Jeremy Veenstra-VanderWeele in the editorial. They are all from Columbia University in New York City.

According to Sandin and colleagues, the new study is the largest and most rigorous yet conducted into the causes of autism. The researchers looked at the medical histories of more than two million children born in Denmark, Finland, Sweden, Israel and Western Australia between 1998 and 2012. All were tracked until 16 years of age. Of the group, just over 22 000 went on to develop an autism spectrum disorder.

Based on the data, about 80% of their risk of developing the condition was due to genetics, with the remainder of the risk tied to as-yet-unidentified environmental causes. Only a negligible amount of risk, about 1%, was due to maternal factors, the study researchers said.

They noted the new numbers are roughly in line with those from prior, smaller studies on the issue, further bolstering their validity.

Dr Andrew Adesman directs developmental and behavioural paediatrics at Cohen Children's Medical Center in New Hyde Park, New York. Reviewing the findings, he agreed that it "provides stronger evidence that autism is mostly due to genetic, and not environmental, factors.

Environmental factors play a smaller role

"Although families are often most concerned about environmental risk factors for autism, the reality is that genetic factors play a much larger role overall," Adesman said.

But he stressed that the findings don't let potential environmental factors – which, unlike genetics, can be changed – off the hook.

"Environmental factors also play a smaller, but important, role," Adesman said, so "this does not mean that we can completely ignore the environmental risk factors and their interaction with the genetic risk factors."

And he noted that despite the new data, "we are not yet able to identify a specific genetic cause for autism in many children." The next step, according to Adesman, is for researchers "to identify more of the different specific genetic differences or abnormalities that lead to autism in an individual child or family."

Image credit: iStock

We live in a world where facts and fiction get blurred
In times of uncertainty you need journalism you can trust. For 14 free days, you can have access to a world of in-depth analyses, investigative journalism, top opinions and a range of features. Journalism strengthens democracy. Invest in the future today. Thereafter you will be billed R75 per month. You can cancel anytime and if you cancel within 14 days you won't be billed. 
Subscribe to News24
Voting Booth
Zama zama crackdown: What are your thoughts on West Village residents taking the law into their own hands?
Please select an option Oops! Something went wrong, please try again later.
Results
Authorities should bring in the army already
10% - 1573 votes
Illegal miners can't be scapegoated for all crime
54% - 8563 votes
What else did we expect without no proper policing
33% - 5326 votes
Vigilante groups are also part of the problem
3% - 508 votes
Vote
Rand - Dollar
16.17
+0.5%
Rand - Pound
19.63
+0.2%
Rand - Euro
16.59
+0.2%
Rand - Aus dollar
11.52
+0.2%
Rand - Yen
0.12
+0.2%
Gold
1,802.29
0.0%
Silver
20.82
0.0%
Palladium
2,227.50
0.0%
Platinum
966.00
0.0%
Brent Crude
98.15
-1.5%
Top 40
63,996
-1.0%
All Share
70,731
-0.8%
Resource 10
64,048
-2.8%
Industrial 25
86,577
-0.6%
Financial 15
16,059
+0.6%
All JSE data delayed by at least 15 minutes Iress logo
Editorial feedback and complaints

Contact the public editor with feedback for our journalists, complaints, queries or suggestions about articles on News24.

LEARN MORE