What causes autism? What we know, don’t know and suspect
One prominent theory that has emerged from brain imaging studies is that some individuals with autism may have under-connectivity in long-range connections, but over-connectivity in short-range connections.
If found to be accurate, these brain differences may be able to explain why some individuals with autism have difficulties with complex tasks that require the integration of information from multiple brain regions (such as cognitive and social abilities), but have no difficulties, or even enhanced abilities, for tasks that require less integration across brain areas (such as sensory processing).
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.
One thought is that the pattern of cell death caused by high testosterone levels may alter brain development in a way that leads to autistic behaviours in childhood. This theory is still to be proven. Again, it is certain that not all individuals with autism are exposed to excessive levels of testosterone in the womb.
The link between gastrointestinal (“gut”) problems and autism is another scientific area that has received a great deal of attention. It is now well known that between 30% and 50% of individuals with autism experience significant gastrointestinal problems, such as diarrhoea, constipation and an irritable bowel.