The Szatmari paper is open-access so it doesn't need any grand details from me... OK, well just a few:
- "Prospective data collected at 4 points from time of diagnosis to age 6 years were used to track the developmental trajectories of children."
- Old reliable ADOS (Autism Diagnostic Observation Schedule) was used "to index the developmental trajectories of autistic symptom severity" alongside the VABS (Vineland Adaptive Behavior Scales) which "assesses child adaptive behavior in the communication, socialization, daily living skills, and motor domains." The immediate difference between these schedules outside of looking at autism symptoms and adaptive behaviours is the reliance on observer scores and parent/caregiver report respectively. Just in case you were worried, the timing gaps between ADOS sessions for example, were probably large enough so as not to lead to any so-called practice effects impacting results. Other psychometric tools were also used to gauge 'trajectory prediction and outcome' including the ADI (Autism Diagnostic Interview) among other things.
- Results: outside of the heterogeneity of symptom presentations, a few key points were noted. So: "Individual children with ASD differ from each other in terms of autistic symptom severity and adaptive functioning from the time of diagnosis in the preschool years, and some of these differences appear to increase by age 6 years." Interesting but not exactly a novel finding as per other discussions in this area (see here).
- "Moreover, change in one domain is not necessarily associated with change in another." In other words, about 20% of their sample showed changes in "adaptive functioning trajectories" indicative of improvement. But that doesn't necessarily translate into similar changes in autistic presentation which were reported to be "more stable" although in about 10% of cases showing "a decrease in symptom severity from baseline to age 6 years."
- In all, the authors report two distinct trajectory groups based on autism severity and three groups for adaptive functioning.
- Caveats? Well, this was a multi-site study in Canada but following diagnosis, participants were not just left without intervention. The Hanen More Than Words® intervention is mentioned as being offered at one site. Indeed the authors note: "the present analysis did not investigate the possible effect of services or opportunities to learn adaptive functioning skills on the developmental trajectories of children with ASD" so one has to be mindful that the results reported might be affected by this variable. Indeed, one would expect trajectory to be potentially affected by such early intervention...
This is interesting work particularly from the perspective of being a longitudinal study which relied on some of the gold-standard tools available to autism psychometric research. I'm really interested in developmental trajectory and autism in light of this area of research highlighting how autism is perhaps better described as the more plural 'autisms' and the breaking down of some sweeping generalisations and dogma which have pervaded autism understanding. That also one or more trajectory might come under the label of 'optimal outcome' (see here), that is moving outside of the diagnostic boundaries of the clinical description of autism, is another important part of this work. Oh, and just in case you think such ideas are bound to just children, think again (see here).
Gender (sex) is also mentioned in the Szatmari paper and the idea that "sex was the only significant predictor of autistic symptom group trajectory membership." The authors continue: "Boys were more likely to be in the group with more severe symptoms and a stable trajectory than girls, who were more likely to be in the group with less severe symptoms and an improving trajectory (controlling for age at diagnosis, cognitive and language scores, and site)." This is really quite an interesting observation and perhaps ties into the idea of sex differences in the presentation of autism (see here) among other things. I'd be interested to see how the gender splits pan out when it comes to those optimal outcomers too as and when larger participant numbers are eventually meta-analysed by someone.
Finally: "earlier age at diagnosis was more likely associated with membership in a group with higher functioning and improving." Going back to my previous point about a possible role for early intervention in developmental trajectory, the idea that earlier diagnosis can make a difference through the use of earlier intervention also potentially gains ground from such observations. Early diagnosis is a primary endpoint for quite a lot of autism research (see here) although with still quite a bit to do in this area (see here).
The Hurdy Gurdy Man to close from The "B.H. Surfers".
 Szatmari P. et al. Developmental Trajectories of Symptom Severity and Adaptive Functioning in an Inception Cohort of Preschool Children With Autism Spectrum Disorder. JAMA Psychiatry. 2015. Jan 28.
Szatmari, P., Georgiades, S., Duku, E., Bennett, T., Bryson, S., Fombonne, E., Mirenda, P., Roberts, W., Smith, I., Vaillancourt, T., Volden, J., Waddell, C., Zwaigenbaum, L., Elsabbagh, M., & Thompson, A. (2015). Developmental Trajectories of Symptom Severity and Adaptive Functioning in an Inception Cohort of Preschool Children With Autism Spectrum Disorder JAMA Psychiatry DOI: 10.1001/jamapsychiatry.2014.2463