Autism: Genetics, Environment, or Both?
Researchers have been debating how much of autism is attributable to genetics vs. environmental (anything that is non-genetic) for decades. While it's an important question, there is unlikely to be one right answer but one thing that virtually all researchers agree on is that BOTH genetics and environment contribute to autism risk.
Given this widely-agreed upon fact, and the uncertainty over exactly how important each one is (which may vary for a given individual), we strongly believe in a balanced research approach that dedicates resources to both camps.
Unfortunately for the past several decades there has been a strong bias in the US, and other countries, in favor of research that emphasizes a view of autism as a primarily genetically driven condition, with far less funding dedicated to non-genetic research. Non-genetic or "environmental" research not only includes classic environmental influences, such as food, air, chemical exposures, but also research that primarily looks at the roles of the immune system, the microbiome, and cell (mitochondrial) metabolism. With the stakes so high, we simply cannot afford to bank on such narrowly focused research. We need to take a broader approach.
One of the ways that researchers have attempted to tackle this question is discussed below.
Researchers have looked at twins where one or both has autism to try and estimate the relative role of genetics vs. environmental factors. Recall that identical twins share virtually all their DNA (and most of their environment) while fraternal twins only share some of their DNA (and most of their environment). By examining how often both twins in a pair have autism autism (the term is called concordance), researchers can make some estimates about genetics and environment.
To take a simple, extreme, example: If it were found that in virtually all cases identical twins both had autism (100% concordance) but in fraternal twins, it was hardly ever the case that fraternal twins both had autism, then one would conclude that environment doesn't matter much. If on the other hand it were if the rate of concordance was the same for both identical and fraternal twins, that would strongly favor environment over genetics, (i.e., the identical genes didn't change things much).
Some early, small twin studies showed low concordance of fraternal twins leading to the early conclusion that autism was primarily genetic and setting the direction for future research.
However, later much larger studies such as this one done at Stanford University or this one in Sweden both put the contribution of environment and genetics in the 50% range each. Recently, the authors of the Swedish study have said that their original approach was flawed and that using a new model, they now arrive at an 83% genetics figure. This debate will likely rage on for decades. In our view, the important thing is that both environment and genetics matter and need to be studied in a balanced way. Unfortunately, due to some of those early, small studies that over-estimated the contribution of genetics, the research focus and funding has been heavily skewed to genetics to the detriment of other promising and important avenues.