One of the great and enduring mysteries of autism is what causes the brain to develop so differently.
The behavioural differences of many individuals with autism are so apparent that it seems intuitive that the causes would also be obvious.
But research over the past 70 years has indicated this isn’t so.
Into this knowledge gap have come all sorts of weird and wacky ideas about the causes of autism: television, power lines, vaccines and sex position during conception.
None have any credence, but have fuelled the mystery surrounding what may cause autism.
In the 1950s and 1960s, there was a widely help belief that autism was caused by parental coldness towards the child.
The term “refrigerator mother” was often directed towards the mothers of these children.
Leo Kanner, the man who first described the behaviours that characterise autism, explored “a genuine lack of maternal warmth” as a possible explanation for autism.
This inaccurate belief left a legacy of shame and guilt in the autism community for at least the following two decades.
Several eminent scientists eventually extinguished the myth.
Two of them were themselves parents of children with autism, and they highlighted a major flaw in the theory: parents who fitted the “refrigerator” stereotype also had children who did not have autism.
Since this time, research has focused on biological factors that may lead to autistic behaviours.
This has found very clearly there is no one cause of autism.
A variety of genetic factors are likely to be the ultimate cause of most cases of autism.
These may work by themselves, or in combination with environmental factors, to lead a child’s brain to develop differently and result in autistic behaviours.
To examine the influences of nature (genetics) and nurture (environment) on a given human quality, scientists study twins.
Recognition has grown over the past decade that aspects of our environment may also contribute to autism.
However, despite substantial research, no one environmental factor has yet been found to be a definite cause of autism.
For a considerable time scientists were searching for one clear brain difference that may be lead to autistic behaviours.
However, this hope has yet to be fulfilled, with few studies identifying brain characteristics that are shared by different individuals diagnosed with autism.
Other biological factors
There is preliminary evidence some but not all individuals with autism are exposed to higher levels of testosterone in the womb.
Excessively high testosterone concentrations in the bloodstream can be harmful and cause cells to die, particularly within the brain, which is highly sensitive to changes in hormone levels.