Anecdotal reports suggest that the presence of behaviours indicative of autism (AD) are displayed at a very early age, with nearly half (31-51%) of all children with AD displaying abnormalities within the first year of life (Gray & Tonge, 2001). Despite this acknowledgment, a diagnosis of AD is typically not being made until a child is much older (Young et al., 2003). These delays commonly occur as a result of the inability of currently used diagnostic criteria (e.g., DSM-IV-TR; ICD-10) to identify and operationalise behaviours relevant to this age cohort. As yet, studies investigating autism during infancy have failed to operationalise behaviours of concern, the age of onset of these behaviours and the impact these behaviours have on development. For example, lack of shared enjoyment and poor eye contact has been identified as early as 11 months, while delayed language, a diagnostic criterion outlined in the DSM-lV-TR, is often not observed until many months later (Young et al., 2003). These results indicate that behaviours indicative of AD emerge at different ages throughout a child’s development with some being modified or ameliorated with maturation or intervention.
The aim of this study was to identify the early symptoms of the disorder and their behavioural presentation to enable us to determine the durability of these behaviours across time and the impact they have on development and prognosis. Specifically we aimed to determine the age at which behaviours commonly associated with AD reliably distinguished AD from children developing typically and children with other disabilities. Of specific interest was whether certain items or behaviours have better discriminating abilities and are of greater clinical significance at specific ages.
The present study involved children aged 12 to 36 months. The development of children with AD was compared to an age matched typically developing group and children with an other disability such as a hearing impairment (ODD) group. Using a number of tools currently used with children of this age (e.g., ADEC, M-CHAT) behaviours were analysed according to four specified age groups.
Variations from typical development were detectable in some children as young as 12 months. In particular, response to name, functional play, and use of gestures, best discriminated between the three diagnostic groups.
The present study was the first of its kind to evaluate the developmental trend of autistic behaviours within children aged 12 to 36 months. The current results suggest clear developmental differences are apparent between the three groups (AD, TD and ODD) from as early as 12 months of age with behaviours specific to autism being clearly identified. It was further evident from the current study that typical development follows a naturally progressive path with an unmistakeable distinction between the diagnostic groups emerging as early as 12 months of age with this difference becoming more apparent by 30 months of age.