21 January 2013

Dr Victoria Burchell By

Appeared in BioNews 689

Rare genetic variant may have a significant impact on a person's risk of developing autism, research suggests. In one of the largest genome-wide studies of its kind, scientists have identified 25 'high impact' genetic variants that are associated with the developmental disorder.

'Many of these gene variants may serve as valuable predictive markers', said Dr Hakon Hakonarson, director of the Centre for Applied Genomics at the Children's Hospital of Philadelphia, who led the study. 'If so, they may become part of a clinical test that will help evaluate whether a child has an autism spectrum disorder'.

Existing genetic test for autism focus on single letter changes in DNA called single nucleotide polymorphisms. The authors of the current study instead investigated the effect of copy number variants (CNVs). CNVs are deletions or duplications of large stretches of DNA, resulting in either an increase or a decrease in the number of copies of genes encoded by that DNA.

In the study published in the journal PLOS ONE, scientists first analysed the DNA from 55 families with multiple members diagnosed with autism spectrum disorders (ASDs) and identified 153 CNVs that could potentially be linked to the disorders. They then investigated the prevalence of these and other previously reported CNVs in 3,000 people with autism and 6,000 people in a control group.

Of these CNVs, 25 novel variants were found to be associated with autism, such that a person carrying the variant was suggested to be twice as likely to develop the disorder as someone who is not.

The study was performed in collaboration with the genetic diagnostics company Lineagen and the authors hope that the newly identified variants will be useful clinically.

'These high-impact variants could be most useful in advising parents who already have one child with an ASD', said Dr Hakonarson. 'If a second child has delays in reaching developmental milestones, testing for these CNVs could help predict whether that child is also likely to develop an ASD'.

Genetic tests for autism are already commercially available, although some scientists and clinicians remain sceptical of the value of this approach. Speaking to the Salt Lake Tribune, Professor Lynn Jorde, chair of the department of human genetics at the University of Utah, said that scientists have identified fewer than 20 percent of the genes linked to autism.

'Any genetic testing is only going to identify a small portion of cases', he said. 'Families should be aware that even if the child has been diagnosed as autistic, genetic testing probably won't find a cause'.