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Rare genetic variants found to play role in development of autism

14 June 2010
Appeared in BioNews 562

Results from the largest ever study of its kind into autism strongly suggests that rare genetic variants contribute far more than common variants to the risk of developing the condition.

The three-year study, led by Dr Stephen Scherer of the University of Toronto and Toronto's Hospital for Sick Children, concludes the second phase of the Autism Genome Project, an international consortium founded in 2002 to facilitate the identification of autism susceptibility genes.

Using microarrays, the researchers studied DNA from 996 primary school children of European ancestry, all of whom had been diagnosed with autism spectrum disorder. The researchers also studied DNA from 1,287 matched individuals with no such diagnosis, who served as the study's control group. The research focused on CNVs (copy number variations ), which are variations in segments of DNA represented either by the presence of extra copies (duplications) or the absence of expected copies (deletions). CNVs are difficult to study, and can demand higher standards of data than other forms of genetic research.

The study discovered a subtle but distinct difference between the CNVs in the experimental group and in the control group. Although there was no significant difference in the number of CNVs per individual in each group, or in the length of CNVs in individuals in each group, there was a significant difference in the location of the CNVs. CNVs were 19 per cent more likely to be located within or near genes in the experimental group than in the control group. This suggests that more genes are disrupted by CNVs in individuals with autism than is the case in individuals without autism.

In many instances, it was established that the disruptive CNVs in the experimental group were inherited from the affected individuals' parents. In some instances, however, the CNVs had arisen spontaneously (de novo). This could have occurred either in the gametes contributed by one of the affected individuals' parents, or in the resulting embryo.

Of the CNVs discovered, some disrupted genes that were already thought to play a role either in the development of autism, or in intellectual development more broadly. But some of the genes disrupted by CNVs in the experimental group had not previously been associated with autism, and were therefore new candidates. At first glance, these new candidate genes appeared to differ vastly between individuals in the experimental group. But patterns emerged when these genes were grouped by function, suggesting a commonality between the biological pathways whose interruption results in autism, even if the mechanism causing the interruption differs.

The study has prompted much speculation about the possibility of developing new diagnostic tests and medical treatments for autism. One of the researchers involved, Professor Tony Monaco of Oxford University, said: 'We do hope to start working with pharmaceutical companies. One hope is that drugs that they might have already developed for other purposes could be used because they have a role in autism'. But while ideas for new drug treatment targets may emerge from the study, the enormous diversity of genes affected in different individuals in the experimental group militates against the development of any universal genetic test.

The charity that publishes BioNews, the Progress Educational Trust, is currently running a project entitled Spectrum of Opinion: Genes Autism and Psychological Spectrum Disorders supported by the Wellcome Trust. A School Resource Pack developed as part of the project will be piloted at Robert Napier School in Gillingham later this month.

Functional impact of global rare copy number variation in autism spectrum disorders
Nature |  9 June 2010
New genetic clues to autism
NHS Choices |  17 September 2021
Study identifies 'many more' autism genes
BBC News |  9 June 2010
26 March 2012 - by Dr Rosie Morley 
Faulty genetic mechanisms particularly active in early life may lead to people developing autism, research suggests...
13 June 2011 - by Dr Lux Fatimathas 
American researchers have linked hundreds of spontaneous genetic mutations to the group of psychological syndromes called autism spectrum disorders (ASDs)...
12 April 2010 - by Dr Charlotte Maden 
A new study into autism has found a link between the disorder in children and their grandparents' age. The research, published in PLoS ONE last week, is the first of its kind to look at grandparent's as opposed to parents' ages...
22 March 2010 - by Dr Charlotte Maden 
New research into diagnostic genetic tests for autism spectrum disorders (ASDs) has revealed the effectiveness of a new test that is currently not used in the first line of diagnosis. The findings were published online last week in the journal Paediatrics....
8 March 2010 - by Sandy Starr 
In their concluding remarks, all three speakers said the answer to the question implicit in the event's title - if you are genetically predisposed to a neurodevelopmental disorder, does this effectively mean you are marked for life? - is an emphatic 'no'. Nonetheless, they had divergent views on the likelihood of successfully applying the fruits of genetic research into mental health...
23 November 2009 - by Heidi Colleran 
In the first study of its kind, researchers in the US have identified a genetic variant that appears to influence both a person's ability to empathise, and how they respond to stress. The research, by a team from Oregon State University and the University of California at Berkeley and published in the journal Proceedings of the National Academy of Sciences, may shed significant light on scientists' understanding of autism, which is characterised by problems with empathy and social communicati...
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