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Autism has been a long enduring mystery of the medical world as to what really causes the brain to develop so differently. The behavioural differences of those with autism are fairly obvious and so the causes should be also. But the research has indicated otherwise. We’ve heard all sorts of theories that cause autism – overhead power lines, vaccinations, sex position during conception and a multitude of absurd theories.
Back in the 1960’s it was thought that autism was a result of parental coldness towards the child. Some people would refer to them as ‘refrigerator mothers’. This was inaccurate belief and sadly left a legacy of shame and guilt in the autism community for many years to come. But many of these parents also had children without autism so the theory was baseless. The research has also tried to pin biological factors as the leading cause but this has since been deemed untrue.
A number of genetic factors are more likely to be the ultimate cause in most children with autism. These may work by themselves or as a combination with other environmental factors that change the child’s brain development and result in autistic behaviour.
Let’s look at a few of these factors:
Researchers examined the influences of genetics and the environment on eleven sets of identical twins where at least one of the twins had autism. Whilst a small study in the late 1970’s, it provided the first evidence that autism was probably a genetic in origin. Further studies have since confirmed this theory. The recurrence risk of a couple who already have a child with autism that may have a second child with autism is approximately 20%.
However, after several decades of intensive research, scientists could not identify just one gene in common from all individuals diagnosed. Thus scientists stopped thinking of autism as one condition with one cause only. It is now widely believed that a number of conditions have clear genetic or chromosomal abnormalities that can lead to autistic behaviour including Down syndrome.
The DNA chain that forms our chromosomes more than 3 billion building blocks that identify small pieces of DNA that may be linked to the development of autism so scientists need to study a very large number of people with autism.
As yet, no study has been able to examine the thousands of people necessary to identify with accuracy all of the small mutations that might lead to autism making identifying just one gene responsible a difficult challenge.
There is a growing theory that aspects of our environment may also be responsible for autism. As yet, no one environmental factor has yet been identified as the single cause.
The most common research technique is epidemiology, which examines how often, and why the diseases occur in different groups of people.
There have been several environmental factors blamed during the prenatal life of a baby. Bacterial or viral infections in the mother during pregnancy have been found to slightly increase the risk of autism. This could be due to the passage of harmful infectious organisms passed on from mother to the baby through the placenta or due to the immune response of the mother being detrimental to the developing brain of the baby.
Another factor that could be related to the environment is the lack of folic acid at the time of conception, the presence of gestational diabetes and possibly the use of certain antidepressants during pregnancy but none of these theories have had conclusive evidence.
Being an older parent, particularly an older father who may be over 50 years at the time of conception, is also another theory that increases the risks.
Few studies have identified brain characteristics that are shared by different individuals diagnosed with autism. This may be further proof that autism has many different causes but it may also be a reflection on the difficulties in studying the brain development. There has been increasing evidence that different brain development may begin prenatally in some people with autism. Newborn babies later diagnosed with autism are often also said to have large heads at birth, known as macrocephaly.
Further research has been conducted on post-mortems of individuals that died prematurely that had autism. After examining the brains of 11 autistic individuals under the microscope, they found changes in the structure and organisation of the brain cells that formed during their foetal life. This indicated differences in brain development could begin very soon after conception.
Previously it was thought that a children’s head circumference in their first 2 years would indicate if they had autism or not, this was often referred to as ‘brain overgrowth’. However, this has since been found to have no link with autism.
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.
The link between gastrointestinal or “gut” problems and autism is another scientific area that has received a great deal of research. It is now well known that between 30% – 50% of those with autism experience significant gastrointestinal problems such as diarrhoea, constipation and an irritable bowel.
While there is currently no evidence for any environmental causes, it is possible subtle influences of the environment may affect individuals differently depending on their genetic make-up, leading to autism in some children.
So clearly, autism has no one single cause and further research is necessary.