Autism is largely down to genes, twins study suggests
By Michelle Roberts Health editor, BBC News online
Individuals with autism have less activity in the amygdala (shown in red), which plays a key role in processing emotions
Genetic influences on autism are estimated to be between 74-98%, a Medical Research Council study of 258 twins suggests.
The King’s College London team said 181 of the teenagers had autism, but the risk was far higher in identical twins where one twin had autism, as they share the same DNA.
The researchers told JAMA Psychiatry that hundreds of genes were involved.
But they do not rule out environmental factors.
Both twins in each pair had been raised by their parents in the same household.
Increased awareness
Autism can be tricky to diagnose. It is a spectrum of conditions rather than a single disorder, and its severity can vary widely from person to person.
Researcher Dr Francesca Happe said, although not perfect, all the evidence pointed to genes playing a bigger role in autism than previously thought.
“Our findings suggest environmental factors are smaller, which is important because some parents are concerned whether things like high pollution might be causing autism.
“Some people think there might be a big environmental component because autism has become more common in recent years but that’s happened too fast for genetics to be a probable cause.
“The main consensus now is that the rise in diagnosis has more to do with increased awareness of the condition.”
Full lives
Dr Happe said what might have been labelled as a learning disability in the past was now being correctly diagnosed as autism.
She said lots of scientists were working to determine which precise genes were involved in autism and whether they were inherited.
“There may be perhaps hundreds of genes that contribute to autistic traits,” she said.
Dr Judith Brown, of the National Autistic Society, said: “Autism is a highly complex story of genes not only interacting with other genes, but with non-genetic factors too.
“This large population-based twin sample is significant because it helps us to understand much more about the role genetics play in autism and opens up the possibility of whole families gaining a better understanding of a condition they may share.
“However, we are still a long way from knowing what leads to autism.
“What people with condition, their families and carers need most of all is access now to the right kind of support to be able to lead full lives.”
Autism
Estimates suggest one in 100 people in the UK has autism
Four times as many boys as girls are diagnosed with autism
The number of diagnosed cases of autism has increased during the past 20 years, reportedly because of more accurate diagnoses
There is no cure, but a range of interventions is available
For more on this story go to: http://www.bbc.com/news/health-31713147
What is autism?
Autism is a developmental disorder that can cause problems with social interaction, language skills and physical behaviour. People with autism may also be more sensitive to everyday sensory information.
To people with the condition the world can appear chaotic with no clear boundaries, order or meaning.
The disorder varies from mild to so severe that a person may be almost unable to communicate and need round-the-clock care.
Research has revealed that people with autism have brains that function in a number of different ways to those without the condition.
One recent study suggested that people with autism tend to have far more activity in the part of the brain called the amygdala when looking at other people’s faces. The over-stimulation of this part of the brain that deals with new information may explain why people with autism often have difficulty maintaining eye-contact.
Specific nerve cells in the brain, called neurones, also act differently in people with autism. Mirror neurones help us mimic useful behaviour so we can learn from others.
Brain imaging studies suggest that the mirror neurones in people with autism respond in a different way to those without the disorder.
This could partly explain what many behavioural studies have already shown – that children with autism can find it difficult to copy or learn simple behaviours from others. Scientists have suggested with social interaction could have a knock-on effect on language learning.
