Autism research in mice has raised the possibility of drugs to treat the condition, BBC news has reported.
The research examined the effect a new drug called GRN-529 had on unusual social behaviour and repetitive motion in mice with autism-like behaviours. These behaviours are similar to those seen in people with autism, who generally have difficulty with social interaction, impaired language and communication skills, and unusual repetitive movements. Current treatments aim to relieve these symptoms through behavioural therapy, but no drug treatments are approved to address these symptoms and there’s no cure for the condition. In the current study, mice given the drug were found to be more social and to repeat motions less often. The researchers say that these results raise the possibility that a single drug may improve some symptoms related to autism.
This was an early, experimental study and its results in mice do not necessarily reflect what will happen in humans. As such, much more research is needed, and it is too soon to say whether this drug will offer a safe and effective treatment option for people with autism.
Where did the story come from?
The study was carried out by researchers from the US National Institutes of Health and the drug manufacturer Pfizer, and was also funded by the two organisations.
The study was published in the peer-reviewed journal Science Translational Medicine.
This story was covered appropriately by the BBC, which not only emphasised the limitations of animal research but also pointed out the difficulties in generalising results from such research to humans. The BBC’s article pointed out early on that “treatments which work in mice frequently fail in humans and potential medication would be years away.”
What kind of research was this?
This animal study examined the effectiveness of a new drug at treating autism-like behaviours in mice, which were bred to behave in autistic ways. These mice demonstrated low levels of social interaction and “communication” (making sounds in response to smells), as well repetitive motions such as grooming and jumping. These behaviours are thought to be similar to the core behavioural symptoms that generally indicate autism in people. They included difficulties or discomfort when interacting with others, difficulties in expressing themselves or empathising and displaying patterns of repetitive movements such as rocking or hand movements.
The causes of autism are still largely unknown, but one area being researched is the way that neurotransmitters work in the brains of people with autism. Neurotransmitters are chemicals that the brain uses to send signals between cells. This research looked at a particular neurotransmitter called glutamate, which plays a role activating neighbouring cells. The researchers thought that giving “autistic” mice a drug that interferes with glutamate may reduce their symptoms. The experimental drug is at an early stage, and is known simply as GRN-529 at present.
Clearly, a mouse that does not make sounds in response to smells is not necessarily the same as impaired communication skills seen in people with autism, and these mice serve as an early research model for developing potential drugs. As such, we cannot say whether the results will be the same in people. It is important to remember that the mice in this study did not have autism, but exhibited behaviours considered to be similar to autism symptoms. This is fairly typical of the way that drug discoveries are made, but a lot more research is needed to further assess the safety and effectiveness of the drug before randomised controlled trials can be conducted with humans.
What did the research involve?
The researchers split the autistic-like mice into four groups: three were given various doses of the drug and the fourth received a dummy placebo drug. They also included an additional control group of mice that did not exhibit any of the autism-like behavioural patterns. The researchers then measured the frequency and duration of the autism-like behaviours in the placebo group and those given the drug to determine whether there were significant differences in their behaviours. The behaviours were measured between 30 and 60 minutes after drug administration.
To assess the effect of the drug on repetitive behaviours, the researchers measured how long, on average, each of the groups spent grooming themselves. In a second repetitive behaviour experiment, they compared the number of times the mice jumped during the assessment period.
To determine the drug’s impact on social behaviours, the researchers put the mice in a chamber that contained both an unknown mouse and an unknown object, and measured how much time the study mouse spent on each side of the chamber, and how much time they spent sniffing the unknown mouse and object. Spending more time with the unknown mouse than the unknown object was taken to signify normal sociability, while spending more time with the unknown object than the unknown mouse was taken to signify impaired sociability. They also allowed the mice to move about freely with other mice, and measured how often the mice sniffed other mice nose-to-nose, approached other mice from the front, and the total amount of time they spent in contact with other mice.
What were the basic results?
When the researchers examined the impact of the drug on repetitive behaviours, they found that mice treated with a medium or high dose of the drug groomed themselves for significantly shorter times than the mice treated with a placebo. Mice treated with a low dose of the drug showed no significant difference in grooming time compared to those given a placebo. Mice given a placebo also jumped significantly more frequently than mice treated at the low, medium and high doses of the drug.
When examining social interaction in the chamber with an unknown mouse and an unknown object, the researchers found that:
- The control mice (which did not exhibit any autism-like behaviours) spent significantly more time sniffing the unknown mouse than the unknown object, signifying normal sociability.
- The placebo-treated mice spent no more time sniffing the unknown mouse than the unknown object, signifying a lack of sociability.
- The mice treated with any dose of the drug spent significantly more time sniffing the unknown mouse than the unknown object, implying a reduction in their impaired sociability symptoms.
- The placebo-treated mice demonstrated a lack of sociability, signified by them spending no more time in the chamber with the unknown mouse than the unknown object.
- A similar lack of sociability was seen in the mice treated with the low and medium doses of the drug, while those treated with the high dose spent significantly more time sniffing the new mouse than the new object.
When examining social interaction in the free movement part of the study, the researchers found that mice treated with the highest dose of the drug spent significantly more time both sniffing nose-to-nose and in social contact with other mice than the placebo-treated mice.
How did the researchers interpret the results?
The researchers say that the drug treatment resulted in improved social interaction and reduced repetitive behaviours in the mice, which are relevant to two of the three core behavioural symptoms of autism in people.
This early-stage animal study provides evidence that a new drug, simply known as GRN-529, may be effective at treating autism-like behaviours in mice. While it may provide clues to the workings of autism, it cannot tell us about whether such treatment would be effective at alleviating behavioural symptoms in people with autism. Also, even if the drug does have an effect in humans, this research offers no guarantees that it will be free from side effects or safe.
There are several key considerations:
- Autism is not a single condition, but a spectrum of disorders. It is unknown how treatment with this drug might affect these core behaviours in the various disorders on the spectrum.
- Several factors are thought to contribute to the development of autism spectrum disorders, including genetics, but the underlying causes of these disorders are unknown.
- The drug used in this study interferes with a key neurotransmitter, glutamate, which plays an important role in our brains. It is unknown at this stage how such treatment will affect other functions and whether there will be unacceptable side effects.
- In addition to the general difficulties of equating mice with people, there are difficulties specific to the mice involved in this study. For example, the main type of mouse used in this research lacked a brain structure called the corpus callosum, which connects the left and right sides of the brain. While the researchers say that feature is similar to a small subset of people with autism who also lack this connection, it is extremely difficult to say how this feature influences the results seen in this study, or how the results would differ if this structure were intact.
This study provides early evidence that a new drug may be of use in altering certain behaviours in mice, rather than humans. Whether this will eventually translate into a drug suitable for treating autism spectrum disorders is unknown, and it will probably take a great deal more animal research before we can build up a fuller picture of its potential.
- Silverman JL, Smith DG, Sukoff Rizzo SJ et al. Negative allosteric modulation of the mGluR5 receptor reduces repetitive behaviors and rescues social deficits in mouse models of autism. Science Translational Medicine, April 25 2012: Vol. 4, Issue 131, p. 131ra51