Autism is a range of conditions collectively known as autism spectrum in social situations when needing to interpret signs of communication between people. Although this is often the case, there is a great range of symptoms across people with autism and these can change over time, making it difficult to define autism or systematically diagnose it.
Autism was first defined in 1943, yet researchers were slow to get a better understanding of the disorder. For many years it was incorrectly believed that emotionally distant mothers were the cause. Even in the mid-1990s it was thought to occur in only 1 in 2500 people. Diagnosed cases of autism have risen sharply over the past 20 years, with 1 in 88 children now diagnosed with autism in the US. This has led to a similarly dramatic increase in the amount of research into the condition.
The varied nature of autism spectrum disorders means that it is unlikely there will be a single cause or cure. It is only by building a repertoire of potential causes that researchers can develop treatments for individual cases.
Mice are an important part of this research as they can model certain aspects of the condition. Researchers study the mice to examine the effects of treatments on the mice's behaviour including sociability, repetitive behaviour and restricted interests. This research has led to several discoveries of potential causes of autism and allowed work to begin on finding treatments.
It is known that over 50% of cases can be attributed to a genetic cause . This means that there is great hope for research into different genes that could trigger autism. Genes such as Shank , PTEN and SLC6A4 have been linked to autism through studies in mice.
Other genes have a direct cause for autistic conditions. For example, Rett syndrome is caused by a mutation in the MeCP2 gene. This disease primarily affects girls, as the gene is on the X chromosome and boys with the mutation often die shortly after birth as they do not have a second copy of the gene like girls. The syndrome can be replicated in genetically modified mice, who suffer from similar symptoms to their human counterparts, such as shortened lifespan, breathing difficulties and behavioural dysfunction . Through the use of this mouse model, several treatments are currently in development for reducing the impact of these symptoms .
A study of two rodent models of autism in 2013 suggested that higher levels of chloride ions in the brain could be a factor in autism
The mice and rats were then given bumetanide, a common drug for high blood pressure that blocks chloride channels in neurons by boosting the effect of the neurotransmitter GABA. This was able to restore chloride levels and brain activity to normal and there were improvements in social behaviours. A clinical trial of bumetanide in children with severe autism has shown improvement to their social interactions and it is hoped that further research can build on this .
It also appears that the bacteria in the body can have an effect on the body’s chemistry. Mice raised with completely no exposure to bacteria have altered brain chemistry and show autistic traits. This could be linked to changes in the amount of GABA and how the brain responds to it. The bacterium Lactobacillus rhamnosus, which is used in dairy products, produces GABA and alters production of GABA receptors in mice, which results in decreased anxiety15 . For another mouse model of autism, the bacterium Bacteroides fragilis improves the behavioural traits and gastro-intestinal problems in young mice .
Another factor linked to autism is inflammation. Although it is a natural part of the body’s protection, too much can be a bad thing. Experiments that have aimed to reduce inflammation in people with autism have shown success. This is despite their rather unusual methods including taking hot baths and swallowing thousands of whipworm eggs. These have both stemmed from anecdotal evidence but are now heading towards clinical trials.
A more severe approach is a bone marrow transplant. Research has suggested that infection in pregnant mothers can lead to an imbalance in the offspring’s immune system, leading to inflammation , . Bone marrow transplants in these offspring in mice have been shown to alleviate some of the autism-like behaviour . A procedure like this for autism patients would be too dangerous and have serious side-effects, but it is hoped that this research will lead to a treatment that can mimic the beneficial effects.
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