Autism has been demonstrated to have a strong genetic basis, though the genetics of the condition are highly complicated meaning that it is not something that is necessarily passed down directly from the parents. It is thought that autism and ASD (Aspergers) is caused by either a rare combination of genetic variants or by one or more genetic mutations. Autism has also been linked to some agents that cause birth defects, offering some support for the latter option. Autism is prevalent in around 1-2 individuals in 1,000, while ASD is more common and affects around 6 in 1,000 and four times as many males as females.
While it has been assumed that autism is caused by a single common genetic or neural cause for autism however, recent research is suggesting that there are in fact multiple autism causes with several distinct aspects that co-occur. Studies of twins have suggested the heritability to be 70% and 90% allowing for variations within the autism spectrum disorder.
Autism causes then are triggered by genetic and environmental factors and result in difficulties in the maturation of the brain. Unlike disorders such as Parkinson’s, there is no clear unifying mechanism in the molecular, cellular or macroscopic levels of the brain. Instead multiple or even all areas of the brain appear to be affected which disturbs the timing of development. These changes are present from a very early age and some studies suggest that neonates only seconds old can already display signs of autism. Interestingly the brain of the autistic child will grow faster immediately after birth, but will then slow down as they become older. This early ‘overgrowth’ is thought to be one of the main autism causes and lead to specialisation in the brain through either an excess of neurons in certain brain regions, disturbed neuronal migration or abnormal formation of synapses. Several neurotransmitter abnormalities have also been suggested to play a role as autism causes. Interestingly autistic patients have higher than normal blood levels of serotonin and several growth hormones.
An interesting and logical theory of autism involves the mirror neuron system – a network of neurons that are known to fire when the individual observes certain emotions, actions and thoughts in others. These neurons are thought to form the basis of empathy and perhaps the development of our theory of mind. Indeed many autistic patients do demonstrate damage in their MNS, but no more so than in other brain areas and this theory does not explain other impaired functions.
Meaning while the underconnectivity theory explains autism causes differently, as being caused by a lack of synchronicity across brain areas in the ‘default network’. This network is responsible for a range of social and emotional processes as opposed to the task-positive network which is used for direction of attention and goal directed thinking and has been shown to be intact in autistic patients. Difficulty has been demonstrated in such individuals to toggle between the two networks, resulting in an excess of low-level processes and difficulties in self-referencing. Another physical difference in the workings of the brain has been demonstrated to be based on changes in event-related potentials. These are signals that fire in response to stimuli, and which are again impaired in autistic patients. For example magnetoencephalography has demonstrated a delay in autistic children’s response to auditory signals at a neuronal level.
Interestingly some studies have managed to imitate the condition of autistic savantism in neurotypical patients by suppression activity in the left fronto-temporal lobe (where language is produced). This results in rapid counting and other savant-like abilities, suggesting that underactivity in some key areas could be responsible for the other behaviours demonstrated in autism. How all these various physical autism causes relate and interplay to create the symptoms of autism and ASD is uncertain, however these findings certainly seem to suggest that difficulties in development result in widespread difficulties across the brain that are nonetheless related.
Cognitive and psychology explanations however meanwhile focus on the more observable psychological autism causes that underly the larger problems. One cognitive theory for example focuses on ‘executive dysfunction’, pinpointing the problem areas as being the working memory, planning, inhibition and other executive function.
Others believe that autistic patients simply lie on one extreme of a scale that has the ability to empathise at one end and the ability to systemise facts about their external world at the other (empathising-systemising). Interestingly this spectrum can be used broadly to describe differences in gender stereotypes, with females falling closer to the empathising end of the spectrum and males the systemising. This becomes more interesting still when you consider that most forms of autism and Aspergers are more common in males than females (other than the completely debilitating Retts syndrome). This can also explain some of the savant abilities that come with 10% of autistic patients and the tendency for compulsive and restrictive behaviour. This has lead some to speculate that autism is in fact an extreme form of ‘maleness’. Here the traits that have proved to have survival value for males, such as a tendency to make collections and the ability to systemise have simply become exaggerated to the point where they are no longer practical and have become autism causes.
Interestingly in some ‘neurotypical’ and healthy patients, obsessive behaviour and lack of social interaction skills often still occur together in individuals branded as ‘geeks’ or ‘anoraks’. In this respect you could even consider autism to be an extreme form of personality disorder where certain traits are exaggerated and others suppressed. As all brains develop differently, it is difficult to consider any brain as ‘neurotypical’. The autistic brain may simply be a certain configuration that is too extreme in certain areas to prove adaptive in today’s society.