Used as we have become to understanding the cause of diseases, we are very often puzzled, even frightened, when we face relatively common conditions for which we have no clear explanation.
Among these, we can include autism, schizophrenia, migraine and a host of other conditions.
And it looks as if the lack of clear evidence for any one cause encourages speculation and belief in a plethora of possible and unlikely reasons.
This is particularly the case for conditions like autism, which presents such a variety of symptoms that these days one tends to avoid the very name and talk about autism spectrum disorders (ASD) to emphasise the variety and range of presentation of the condition.
A child with ASD usually looks normal and behaves normally at first, but within months, worrying signs start appearing: delayed development, unresponsiveness to contact, avoidance of eye contact.
Later on, it looks as if the child has withdrawn from the surrounding world, preferring to live in a cocoon of isolation.
One recent description of the manifestations of autism may be found in an excellent book Far From the Tree, by Andrew Solomon (2012).
A number of causes have been brought forward to explain the condition, which have been conclusively shown to be irrelevant. Theories blaming maternal behaviour (refrigerator mother!) or vaccination in childhood have succeeded in causing considerable anxiety and have even led to complications, but have been conclusively ruled out as irrelevant.
The following are some established causal associations for which there is a considerable amount of evidence:
A marked increase in incidence in recent years: the Autism Society of America estimates that in the US, there are currently about half a million people with this condition, which is growing at the rate of 10-17 per cent per year. In Malta, while general statistics about prevalence of the condition are not available, the Autism Parents Association (APA) claims there are 120 families having a child with this condition.
• Increase in paternal age (four times higher prevalence when fathers are in their 30s, compared with those in their 20s).
• A strong genetic basis: a much higher incidence (60 to 90 per cent in identical twins and 20 to 30 per cent in non-identical twins. Siblings of children with autism are 20 times more likely to have the condition compared with the general population.
• Occurs twice as commonly in males than in females.
There is no question that there is a strong genetic component underlying tendency to heredity, which is found in about 30 to 70 per cent of cases.
There is not one single gene that is responsible, but it is more likely that there are multiple ones scattered throughout the whole genome which have some bearing on the expressivity of this condition, i.e. what spectrum of symptoms are likely to become evident in the affected child.
But, likewise, the evidence suggests that there is also an environmental factor, including possible factors acting during pregnancy.
Recent experimental research throws some very interesting light on the cause and possible management of autism. Pregnant mice were first made to show autistic manifestations by injecting them with a chemical that mimics viral infections.
Mice born from this procedure were less sociable and more anxious than normal mice. They also had intestinal symptoms (leaky guts) – a condition that is also not unusual in children with autism.
The interesting thing about this finding is that these mice were found to have lower levels of the gut bacterium bacteroides fragilis, and when they were fed this bacterium, their symptoms, both gut and behaviour-related, returned to normal.
One might ask: what is the link between a common gut bacteria and brain pathology? These researchers found that these mice had levels of a certain chemical (4EPS), which were 46 times higher than normal, and that moreover, when this substance was injected into normal mice, they exhibited behavioural symptoms similar to the autistic mice.
It looks as if the child has withdrawn from the surrounding world, preferring to live in a cocoon of isolation
What works in mice does not necessarily translate to the human situation. However, a curious link is the one between this chemical and another (para-cresol), which is found to be elevated in people with autism. In other words, mice rendered autistic experimentally and children with autism were found to have an excess of closely related chemicals in their blood.
It could be argued that in the case of autistic mice, an altered gut flora is responsible for abnormal metabolism with the production of toxic substances. If this link is substantiated, it will provide justification for a trial of probiotics, which help restore normal bacterial flora to the gut.
In the words of gastroenterologist Stephen Collins of McMaster University in Ontario, Canada: “I think there is now sufficient proof of concept where people can start to look at probiotic bacteria to improve brain function in humans.”
mnc25@optusnet.com.au