Is genetic testing for autism possible?

Scientists investigate the use of genetic testing for ASD, and whether it can predict if children are likely to develop autism spectrum disorder.

Autism spectrum disorder (ASD) is a set of complex brain development disorders and is characterised by three main features; impaired social interaction, restrictive interests, and repetitive behaviours. ASD is usually diagnosed during childhood.  It is important to note that ASD is a spectrum of disorders meaning that no two individuals with ASD will experience the same set of cognitive defects and behavioural manifestations. This makes it difficult to diagnose and even more challenging to determine the cause for ASD development, but is genetic testing for ASD possible?

Genetic testing for ASD

In a recent Canadian study published in Nature Communications, scientists wanted to know if they could use genetic screening to predict if children were likely to develop ASD. Specifically, they were interested in investigating the younger siblings of children who had already been diagnosed with ASD. The researchers used information from the Baby Siblings Research Consortium (BSRC) to track families that had at least one child diagnosed with ASD. They then followed the progress of 288 infant siblings (younger siblings) to determine whether or not these siblings would be diagnosed with ASD.

The researchers then analysed the genetic information from 253 older siblings that had already been diagnosed and found fifteen genetic signatures (known as copy number variants) that were ASD-relevant. When the scientists looked for these signatures in the younger siblings 13 of the 288 children had ASD-relevant gene signatures. The researchers were able to show that eleven of 157 younger siblings who developed ASD or who were developing atypically at the age of three carried these specific genetic signatures.

Can genetic signatures be used to predict whether a child will develop ASD?

The team then went on to do computational analysis using only the genetic signatures that were associated with pathogenic genes (changes in DNA that are likely to contribute to the development of ASD). They showed that these genetic signatures had a positive predictive value of 0.50 for ASD and 0.83 for combined ASD/atypical development in younger siblings. The researchers went on to analyse the presence of these genetic signatures in a different dataset, they analysed data from 2110 families from the Simons Simplex Collection. They found a positive predictive value for ASD of 0.79 and 0.83 for ASD/atypical development.

This work is important because it could provide a basis for genetic testing for ASD, which could help diagnose children before symptoms develop. This genetic screening could have the potential to inform doctors on whether or not intensified surveillance is required for infants who have an increased risk of developing ASD. Although there is potential for this work to become a diagnostic tool there are some limitations to keep in mind.  The database the team used to run this analysis (BSRC) has an over-representation of ASD in the sample, which may bias the statistical analysis. They only looked at children who were diagnosed by the age of three, which is challenging as these diagnoses can change throughout development and siblings deemed non-ASD may only be diagnosed later in life. There were very few participants in both databases with ASD relevant genetic signatures which limits the statistical power of the analysis and makes it difficult to apply the findings to different populations.

Dr. Lonnie Zwaigenbaum, a lead author on this study discussed the implications of their work in a press release stating that “At this point, we can’t fully determine the anticipated severity of a child’s future symptoms. What we can say is that it’s important to closely monitor their development and start therapeutic interventions early to support their skill development and address emerging functional impairments related to ASD.”

More about ASD

What causes ASD?

ASD is a heritable condition with a major genetic component that shows a complex pattern of inheritance. This means that there isn’t a single gene responsible for the development of ASD, rather a number of different gene mutations can all interact with each other and the environment to contribute to different aspects of the disorder.

Treatment options for ASD

There is currently no cure for ASD, there are however behavioural interventions that have been shown to be effective at improving social and communication skills, cognitive ability, and management of problem behaviours. There is also substantial evidence to show children who receive behaviour interventions before the age of four or five have improved outcomes compared to older children who enter treatment programs. The prevalence of ASD (1 per 160 children worldwide), its severity and the benefits of early intervention all highlight the importance of early diagnosis.

ASD diagnosis

Currently, the only way to diagnose children with ASD is through the use of parental questionnaires and behavioural observations. There are limitations to this type of diagnostic technique and it has been estimated that 80% of children diagnosed with ASD by the age of seven are missed by initial screens (Checklist for Autism in Toddlers or CHAT) conducted at 18 months. There is also a lack of knowledge of how the early symptoms of ASD develop in children making diagnosis difficult. The variety of behaviours and symptoms present in ASD is another challenge to an accurate diagnosis.

Written by Tarryn Bourhill Msc, PhD Candidate

References:

1. Lord, C., Cook, E. H., Leventhal, B. L. & Amaral, D. G. Autism spectrum disorders. Neuron 28, 355-363 (2000).

2.  Bryson, S. E., Rogers, S. J. & Fombonne, E. Autism spectrum disorders: early detection, intervention, education, and psychopharmacological management. The Canadian Journal of Psychiatry 48, 506-516 (2003).

1. Corsello, C. M. Early intervention in autism. Infants & Young Children 18, 74-85 (2005).

2. Dawson, G. & Burner, K. Behavioral interventions in children and adolescents with autism spectrum disorder: a review of recent findings. Current opinion in pediatrics 23, 616-620 (2011).

3. Kumar, R. A. & Christian, S. L. Genetics of autism spectrum disorders. Current neurology and neuroscience reports 9, 188-197 (2009).

4. Cantor, R. M. Molecular genetics of autism. Current psychiatry reports 11, 137 (2009).

5. Yoo, H. Genetics of autism spectrum disorder: current status and possible clinical applications. Experimental neurobiology 24, 257-272 (2015).

6. WHO. Autism spectrum disorders, <https://www.who.int/news-room/fact-sheets/detail/autism-spectrum-disorders> (2019).

7. D’Abate, L. et al. Predictive impact of rare genomic copy number variations in siblings of individuals with autism spectrum disorders. Nature Communications 10, 1-9 (2019).

8. Neitz, R. Genome testing for siblings of kids with autism may detect ASD before symptoms appear, <https://www.eurekalert.org/pub_releases/2019-12/uoaf-gtf120219.php> (2019).

Image by Gerd Altmann from Pixabay