Autism spectrum conditions (ASC) are a spectrum of developmental conditions characterized by deficits in social communication and restrictive patterns of behaviour. Some of the key features of the condition, such as repetitive behaviours, sensory issues and difficulties understanding social cues, can be classed as ‘autistic traits’ that are seen in the general population to a lesser degree. Indeed, it is now believed that ASC refer to a subset of the population that lie on one extreme of the normal distribution of autistic traits across the general population.
A study out this month, from the Autism Research Centre, carried out a large-scale analysis of autistic traits in siblings of individuals with ASC, who themselves do not have a diagnosis. The study, led by PhD student Emily Ruzich, aimed to better understand the heritability of these traits by investigating whether these unaffected siblings showed a greater degree of autistic traits than the general population.
Participants for the study were recruited into 3 groups: individuals with a diagnosis of ASC, individuals without a diagnosis but with a sibling who had a diagnosis of ASC and individuals without a personal or family history of the condition. This allowed the researchers to contrast the level of autistics traits found in the unaffected siblings with the other two groups. Both males and females were included across the 3 groups, so that the researchers could explore whether sex differences resulted were associated with in siblings displaying different levels of autistic traits. The study boasted an impressive number of 4818 participants, recruited from the Cambridge autism research database.
The study was conducted entirely online by asking participants to fill out details on their family history of the condition and complete questionnaires on their personality. One of these questionnaires was the autism quotient (AQ) that measures autistic traits in the general population. The researchers used a cluster analysis approach, where data is analysed to see if participants tend to group around certain score values, to better understand how unaffected siblings tend to score on measures of autistic traits.
The sibling group showed an intermediate level of autistic traits in comparison to the general population and individuals with a diagnosis. The analysis also revealed that the unaffected siblings clustered quite distinctly into two groups: the first and smaller group showed a very similar level of traits to diagnosed individuals. The second and larger group showed a lower level of autistic traits, as expected in the general population. The results reveal the diverse nature of the sibling group and suggest that while many unaffected siblings show a relatively low number of autistic traits, a subset of these siblings have a closer resemblance to the ASC group.
The authors note that having participants self-report their diagnosis runs the risk of some individuals being included into the wrong groups and consequently used comprehensive screening methods to ensure that such incidences were kept to a minimum. The fact that the study was carried out entirely online made it highly accessible and inclusive which no doubt lead to the impressive number of participants taking part in the study.
We spoke to the lead author Emily Ruzich about the implications of the study:
“The finding that siblings, like parents, may exhibit a form of the ‘broader autism phenotype’ has implications for understanding the aetiology of autism; and further, our results indicating that siblings come in two ‘flavours’ show how complex and nuanced autism is as a condition. Further research may lead not only to greater understanding of this condition, but also potentially to improved identification of those on the spectrum.”
Written by Owen Parsons.