People with autism have too many synapses in their brains, say researchers
Scientists say they have discovered the reason why some people suffer from autism.
Those with the condition have too many synapses in their brains – places where where neurons connect and communicate, a new study has found.
Scientists at Columbia University in New York believe that the surplus synapses are created because of a lack of ‘pruning’ that normally occurs early in life.
The discovery is a huge leap in understanding of the complex condition and creates hope of a possible treatment, researchers said.
In mice with autistic traits, scientists were able to restore the synaptic pruning and reduce symptoms.
Using a drug usually used to suppress the immune systems of transplant patients, the found the autistic-like behaviors were reduced.
The drug, rapamycin, has side effects that make it unsuitable as an autism treatment.
But the discovery opens up possibilities for other therapies which can reduce the number of synapses, according to the study published in the journal Neuron.
Professor Jeffrey Lieberman, chair of psychiatry at Columbia University Medical Center in New York, where the research took place, said:
‘This is an important finding that could lead to a novel and much-needed therapeutic strategy for autism.’
Autism, which affects around 700,000 people in the UK [the situation in United States is more dramatic: Autism rates – 1 in 68 U.S. children], covers a range of behavioral disorders that reduce the ability of sufferers to communicate with and relate to other people.
It is believed to be triggered by a combination of genetic and environmental factors that impact on the developing brain.
During normal brain development, a burst of synapse formation occurs in infancy, especially in the cortex – a region closely linked to autistic behavior.
Pruning removes more than half of these cortical synapses by late adolescence.
Synapses are known to be affected by many genes linked to autism, leading to speculation about the role they play in the condition.
The Columbia University scientists examined the brains of 26 autistic children and young people aged two to 20 who had died from a variety of causes.
By late childhood, the researchers found that spine density had dropped by about half in the healthy brains, but by only 16 per cent in the brains of autistic individuals.
Lead researcher Professor David Sulzer said:
‘It’s the first time that anyone has looked for, and seen, a lack of pruning during development of children with autism, although lower numbers of synapses in some brain areas have been detected in brains from older patients and in mice with autistic-like behaviors.’
In laboratory mice, the pruning problem was traced to a protein called mTOR which when over-active suppressed the ability of brain cells to prune themselves.
Large amounts of the over-active protein were also present in the brains of autism sufferers, the scientists found.
Rapamycin inhibited mTOR and restored normal autophagy and synaptic pruning in the mice, even at a late stage when the animals were already displaying signs of autism.
Professor Sulzer said:
‘The fact that we can see changes in behavior suggests that autism may still be treatable after a child is diagnosed, if we can find a better drug.’
He added: ‘While people usually think of learning as requiring formation of new synapses, the removal of inappropriate synapses may be just as important.
‘What’s remarkable about the findings is that hundreds of genes have been linked to autism, but almost all of our human subjects had overactive mTOR and decreased autophagy, and all appear to have a lack of normal synaptic pruning.’
Carol Povey, director of the National Autistic Society’s Centre for Autism, said:
‘This interesting research may help develop our understanding of the complex brain differences that exist between people with autism and those who do not have the condition.
‘However, the suggestion that a drug could be developed to ‘treat’ autism should be treated with caution. Aside from considering the ethical implications, we question whether it’s possible to extrapolate the effects of medication on mice that exhibit supposedly autism-like behaviour to humans who actually have the disability.’
Source | DM