Written by Amy Norton HealthDay Reporter >
Thursday, January 6, 2022 — A small study finds that a drug that acts on specific brain receptors can temporarily relieve visual processing problems in some adults with autism.
The researchers said it’s too soon to know if arbaclofen could be helpful in managing these visual problems. But they said the findings give insight into the brain differences that support them.
Autism is a developmental disorder of the brain that causes varying degrees of impairment in communication and social skills.
People with autism are often hypersensitive to certain stimuli but unresponsive to others. They may have difficulty tolerating bright or fluorescent lights or the feel of certain fabrics, or they may have trouble distinguishing between conversation and background noise, for example.
One general theory is that autism involves an imbalance in signals in the brain – including the circuits that control sensory processing.
Research in recent years has indicated that a neurotransmitter called GABA is one of the key players. Neurotransmitters are chemicals that transmit messages between brain cells, and GABA is an inhibitory neurotransmitter — which means it helps communicate these signals.
Arbaclofen, an experimental drug, works by activating specific GABA receptors on cell surfaces.
And in the new study, scientists found that a single high dose of the drug disrupts visual processing in people without autism — but often improves it in people with the disorder.
“Previous research on GABA in autism spectrum disorder has been largely indirect,” said lead researcher Dr Greene McClonan, Professor of Translational Neuroscience at King’s College London.
She said that GABA genes sometimes change in people with autism, while studies of autopsied brain tissue have found some autism-related differences in the GABA system.
“Here we have provided direct, in vivo human brain evidence that GABA regulation of visual processing differs in people with and without autism,” McClonan said.
Alicia Halladay, chief science officer of the nonprofit Autism Science Foundation, was not involved in the study. She agreed with findings that GABA is “significantly involved” in visual processing, and that altering the chemical pathway may alleviate visual problems for some people with autism.
Nobody is saying GABA is the whole story, or that arbaclofen may be beneficial for all people with autism.
McClonan noted that the study group was fairly small: 19 adults with autism spectrum disorder and 25 without them. But even within that small group of autistic people, the individuals were diverse.
Some have a “sensory processing profile” that is very similar to that of unaffected participants, McClonnan said.
“For these individuals, we might expect that targeting GABA signaling would not be beneficial,” she said.
Another study is underway to test arbaclofen, as part of a large research project called AIMS-2-Trials. McClonnan said the overarching goal of these studies is to better understand the mechanisms behind autism, and how they differ between individuals — and ultimately to tailor treatments to individuals.
Current Study – Published Jan 5th in Translational Medicine Sciences -Included 44 autistic and non-autistic adults who made up to three study visits. In all of them, they were given either a low or high dose of arbaclofen or a placebo.
The participants then underwent a specialized brain scan that allowed GABA concentrations to be measured in the brain, followed by testing their visual processing. It included distinguishing cues that are visible in the foreground from those in the background.
In general, people with autism had more difficulty with the task when given a placebo. However, when taking a high dose of arbaclofen, visual processing generally improved — while it got worse among the non-autistic participants.
There are a lot of questions ahead. Halladay noted that this study involved testing vision in the lab: whether the drug would be useful for people in the “real world” – with many simultaneous sensory experiences – is unknown.
GABA is also thought to be involved in processing other sensory information, including sound and touch. Halladay said it’s not clear if this drug might be helpful in resolving problems with these stimuli.
The broader question is whether relieving sensory difficulties can improve some behaviors common in autism.
Halladay explained that sensory overload is stressful and can cause a “physical and emotional shutdown” for people with autism. Behaviors such as staying away from touch, or using repetitive sounds and movements, are ways to deal with these sensory issues.
“ASD will never be simplified strictly into a single mechanism, as it is individually complex and highly [variable]McClonan said.
But, she added, even complex human behavior is built on “foundational processes,” including the ability to process sensory information.
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Posted Jan 2022