The actual, definite cause of both Autism and Asperger's Syndrome remains a mystery. Despite many theories being proposed and suggested over the years, there has never been any definite proof or evidence to link the conditions to a direct cause or causes. Indeed, all we can do at the present moment in time is speculate.
It is a mystery why some people develop Autism and others Asperger's Syndrome and others don't develop either. For me, that is an equally as big a mystery as to why either Autism or Asperger's Syndrome develop in the first place.
It has been suggested that ASC's can be transmitted on a genetic basis, or that there is some genetic component or link determining the conditions. This has been seen in families where a person has had Asperger's Syndrome and their parents or grandparents have displayed behavioural habits, which have been very similar. There have been families in which one child has had Asperger's Syndrome, and other children have had Autism. Studies of identical twins who share exactly the same genetic material and non-identical twins have shown that Autism is more common in identical than non-identical twins. Indeed, autoimmune disorders are higher in families with children with Autism and AS such as Hypothyroid, Diabetes and Rheumatoid Arthritis.
One problem with the genetic theory is knowing how many Autistic and Asperger people have children. A likely cause in my estimation is that the genetic susceptibility is there in someone with the condition, but something extra is needed to bring it out or for it to fully develop, be it mercury, illness or infection, or some other factor.
Some findings and studies have illustrated that Autistic people have abnormalities in the frontal and parietal lobes of their brains. Autopsies have also revealed that in the brains of those with AS, present are different structural developments in the Cerebellum and Amygdala. In those with low-functioning Autism, the differences in brain structures have been seen in the Cerebellum and Hippocampus. In individuals with both conditions, particularly Asperger's, the Cerebellum, which is a mini-brain, at the back of the brain, has been noted to be smaller and immaturely developed. When Temple Grandin, an Autistic woman, had an MRI scan taken, it revealed that her Cerebellum is smaller those which NT's have. In the human brain, the Hippocampus's role is to make it possible to recall recent experiences and information, whereas the Amygdala directs our emotional responses. It also processes emotion.
Brains from low-functioning Autistic people are more immature in the development of the Hippocampus than in those with Asperger's Syndrome, which is more typical. This may help to explain the cognition problems in low-functioning Autism, which those with Asperger's Syndrome don't experience. With regards to the Amygdala, the Asperger brain is more abnormal than the Autistic brain.
In an experiment, NT's and Aspies looked at photographs of people's eyes (which also show the eyebrows, and parts of the nose and forehead), and attempted to guess what the people were thinking. When the participants were performing the task, their brains were scanned using an MRI machine. Naturally NT individuals performed very well on this task, whilst those with AS performed very poorly.
High levels of the neurotransmitter Serotonin have been found in a number of people with both Autism and Asperger's. Since neurotransmitters are responsible for passing nerve impulses in the brain and nervous system, it is possible that they are involved in the distortion of sensations that accompanies both conditions, and why both are hypersensitive to touch, sound, smell and taste, and find it very hard, if not impossible, to filter out these distractions, which NT's can. The nerve endings appear to be longer in the Autistic/AS brain than the NT brain, again accounting for their hypersensitivity to sound and touch.
In another experiment, Professor Simon Baron-Cohen carried out further functional MRI studies on those with AS and NT's alike. They formed his control group. The conclusions indicated that NT's activate the amygdala to judge the expression in another person's eyes, but people with Asperger's use the fronto-temporal regions of the brain. There are fewer Cerebellar neurons in those with ASC's, suggesting that Autism and AS may be caused by interrupted brain development in the fetus.
An Australian scientist, after conducting some research, believed that the brains of Autistic savants don't analyze and edit incoming information like NT brains, and as a result, that is what gives them their amazing, if unbalanced and uneven skills.
It has been suggested that Autistic Spectrum Conditions are on the increase. However, there are those who believe that the increase is due to more and more people being diagnosed, along with increased awareness of Autistic Spectrum Conditions.
I agree with the latter view. However, whilst agreeing, perhaps the increase could be due to the chemicals used in fertilisers, Mercury, as some people are susceptible to it and some of the E-numbers and colours used in food ingredients. This may increase some people's vulnerability to both Autism and AS. The latter, combined with e-numbers, colours and additives, is certainly known to make the symptoms of AS and Autism more pronounced.
Problems have been shown at Chromosome 15 and Chromosome 7 and the X-Chromosome in individuals with Autism and AS, in several studies, but no full, conclusion can be drawn of any particular or specific cause or causes, to date.
