Autism, or autism spectrum disorder, refers to a range of conditions characterized by challenges with social skills, repetitive behaviors, speech and nonverbal communication, as well as by unique strengths and differences. We now know that there is not one autism but many types, caused by different combinations of genetic and environmental influences.
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. Animal testing allows researchers to study the mice and examine the effects of treatments on the mice's behaviour including sociability, repetitive behaviour and restricted interests. These animal experiments 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 causemice.
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. These aniaml experiments preceded 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.
26/06/18 Autism traits could be 'edited' out genetic trial suggests
02/05/18 Autism test and treatment on horizon as scientists find hormone deficiency link
A test and possible treatment for autism could be on the horizon after scientists discovered that people and primates who are less social are deficient in a particular hormone. In tests on rhesus monkeys, they found that less social animals had levels of the hormone which were almost one third lower than their more gregarious peers. And a similar deficiency was found in 14 autistic boys. Although the results are preliminary, the researchers believe their findings suggest that AVP may not only provide a test for autism, but also be a target for developing drugs to alleviate social impairment.
23/03/18 How Much Can a Mouse Truly Reveal About Autism?
The ideal “autism mouse,” researchers thought at the time, should show all the same traits that characterize autism in people: language and social problems, and restricted and repetitive behaviors. Some mutant mice make fewer ultrasonic vocalizations than controls do, which many behaviorists took to be an analog of language problems. Other models groom, jump, or bury marbles to an excessive degree—actions the researchers interpreted as repetitive behaviors reminiscent of autism. But researchers were most intent on sniffing out social deficits, a hallmark feature of autism. If they could pin down a murine model of this trait, the thinking went, perhaps they could design drugs to address it—or could at least better understand the brain pathways involved.
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Last edited: 9 March 2021 09:37