Research Studies

A Study of Infant Siblings of Children with Autism Spectrum Disorders

What is new and exciting with the Sibling Study?

This is a short summary of what we are learning about early development in autism.
Over the past 5 years the Canadian Sibling Study has worked with infant siblings of children with ASD and their families to better understand early development in this at-risk group, and specifically, early behavioural signs associated with ASD. Currently, there are 310 infant siblings and their families participating in the study.

Results thus far indicate that by 12 months of age, children who are later diagnosed with autism show decreased eye contact and social smiling, do not consistently respond when their name is called, show less interest and positive emotion during social interactions and tend to visually fixate on toys and other objects (Zwaigenbaum et al., 2005). In siblings subsequently diagnosed with ASD, parents report communication delays based on observations at home, not only in the use of words, but also gestures by the age of 12 months (Mitchell et al., 2006). There is a remarkable consistency between behaviours that we see during study visits, and what parents of the same infants report on questionnaires. Review of videotapes of our study visits has also allowed us detect specific repetitive behaviors that are apparent by 12 months and may also aid in early detection (Loh et al., 2007).

Within the group of siblings who go on to be diagnosed with ASD, there appears to be at least two subgroups. The first subgroup of children develops signs of ASD by 12 months of age, often coinciding with a leveling off of their language and cognitive development, such that the delays and functional impairments become more and more significant between ages 1 and 3 years. What has been somewhat surprising is that early signs are not obvious to us (or to parents) at 6 months of age (Zwaigenbaum et al., 2005), but rather, appear to emerge and/or progress between 6 and 12 months. In the second subgroup of children, the signs may be more subtle and more difficult to detect prior to age 18 months, and language and cognitive abilities are less delayed and follow a more typical developmental course (Bryson et al., 2007). In general, we have found that children with ASD whose language and intellectual skills are in the average range at the time of diagnosis have early signs that are more difficult to detect during infancy. In fact, despite our best efforts, this group is less likely to be diagnosed before the age of 3 years than children who are more developmentally delayed (Zwaigenbaum et al., in preparation). Learning more about early signs in children with ASD in this higher functioning group will be very important, as we want to make sure that all children on the autism spectrum are diagnosed as early as possible.

In summary, our work with infant siblings of children with ASD has helped us learn about how autism emerges early in life across the range of symptom severity and functional ability, and has provided direction to other research groups studying similar issues (Zwaigenbaum et al., 2007).

References
Bryson SE, Zwaigenbaum L, Brian J, Roberts W, Szatmari P, Rombough V, McDermott C. A prospective case series of high-risk infants who developed autism. J Autism Dev Disord. 2007 Jan;37(1):12-24.

Bryson SE, Zwaigenbaum L, McDermott C, Rombough V, Brian J. The Autism Observation Scale for Infants: Scale Development and Reliability Data. J Autism Dev Disord. 2007 Sep 14; [Epub ahead of print]

Loh A, Soman T, Brian J, Bryson SE, Roberts W, Szatmari P, Smith IM, Zwaigenbaum L. Stereotyped motor behaviors associated with autism in high-risk infants: a pilot videotape analysis of a sibling sample. J Autism Dev Disord. 2007 Jan;37(1):25-36.

Zwaigenbaum L, Bryson S, Rogers T, Roberts W, Brian J, Szatmari P. Behavioral manifestations of autism in the first year of life. Int J Dev Neurosci. 2005 Apr-May;23(2-3):143-52.

Zwaigenbaum L, Thurm A, Stone W, Baranek G, Bryson S, Iverson J, Kau A, Klin A, Lord C, Landa R, Rogers S, Sigman M. Studying the emergence of autism spectrum disorders in high-risk infants: methodological and practical issues. J Autism Dev Disord. 2007 Mar;37(3):466-80.