Five countries, two million people, and 16 years of research has revealed what has already been repeated time and time: vaccines are not the leading cause of autism spectrum disorders (ASD).
The study was published this week via the American Medical Association's JAMA Psychiatry, with researchers confirming that "the heritability of ASD was estimated to be approximately 80%, indicating that the variation in ASD occurrence in the population is mostly owing to inherited genetic influences."
"Everywhere we looked, in five different samples, what we saw was that genetic factors were most important," commented lead researcher Sven Sandin in a HuffPost interview.
The Karolinska Institute researcher and his team say their findings have uncovered nothing new, but what is significant about this latest research is the magnitude.
"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," reports Health24.
The study also rules out "maternal effects" like weight and diet during pregnancy, and birth methods with data showing a 0.4% to 1.6% probability of maternal effects causing ASD.
"On some level, I feel like we should feel comforted by [these findings]. Because it's almost like autism is explained ... it's not because of what a parent is doing right or wrong," Dr Wendy Sue Swanson, an American paediatrician, has said about the study.
But what about the other 20%?
Sven admits that although wide-ranging, this study is just the tip of the iceberg.
"We still do not know which specific genes contribute to risk. Also, there are numerous potential environmental factors that could be related to ASD, either directly or acting together with genes. We have, so far, only been scratching the surface."
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