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Long-Term Symptom Reduction Following the Preschool Autism Treatment Trial RCT (PACT)
Objectives: To determine long-term outcomes of the Preschool Autism Communication Trial (PACT). We hypothesised enhanced intervention effect on autism symptom outcomes, and continuation of effects on parent and child social interaction.
Methods: PACT tested a 12-month parent-mediated social communication intervention for children aged 2 - 4 years with severe autism (18 therapist-parent video-aided sessions and daily parent home-practice), randomized 1:1 against Treatment as Usual. We undertook follow-up ascertainment at all original trial sites (Manchester, Newcastle, and London, UK) at median 5·75 years (IQR 5·42–5·92) from the original trial endpoint. Pre-specified blinded primary outcomes were the Autism Diagnostic Observation Schedule Combined Severity Score (ADOS CSS); proportion of child dyadic initiatiations with parent from the Dyadic Communication Assessment Measure for Autism (DCMA), and an expressive-receptive language composite. Secondary outcomes included non-blinded parent-ratings of autism symptoms (SCQ), repetitive behaviours (RBQ), adaptive behavior (Vineland), and peer relationships (SDQ); teacher-ratings of adaptive behavior (Vineland). All analyses were by intention-to-treat. Study registration ISRCTN 58133827; funding UK Medical Research Council.
Results: 121 (80%) of the 152 trial participants (59 [77%] of 77 assigned to PACT intervention vs 62 [83%] of 75 assigned to treatment as usual) were traced and consented to be assessed. Mean age at follow-up was 10·5 years (SD 0·8). Group difference in favour of PACT on ADOS CSS was logodds effect size (ES) 0·64 (95% CI 0·07 to 1·20) at treatment endpoint and ES 0·70 (95% CI –0·05 to 1·47) at follow-up, giving a significant overall reduction in symptom severity over the course of the whole trial and follow-up period (ES 0·55, 95% CI 0·14 to 0·91, p=0·004; Figs 1 and 2). Figure 2 shows group time paths in relation to baseline (left) and TAU (right). DCMA child initiations at follow-up showed a Cohen’s d ES of 0·29 (95% CI –0.02 to 0.57) in favour of PACT and was significant over the course of the study (ES 0·33, 95% CI 0·11 to 0·57, p=0·004). Non-blind parent-rated autism symptoms (ES 0·40, 95% CI 0·05, 0·77) and repetitive behaviours (ES 0·87, 95% CI 0·47, 1·35) showed comparable treatment effects (Fig 1). There were no group differences in the language composite (ES 0·15, 95% CI –0·23 to 0·53) or comorbid mental health problems.
Conclusions: This study supports the clinical value of the PACT intervention. It advances previous work by showing for the first time that a theoretically derived, developmentally targeted early intervention can have a sustained effect on autism symptom outcomes nearly 6 years after the end of treatment in a randomised trial. Such a sustained effect after time-limited intervention has implications for developmental theory and further research is needed to elucidate the developmental mechanisms. Strengths are the pre-specified ITT analysis on standard blinded outcomes and nearly 80% follow-up of one of the largest autism treatment cohorts. We cannot be sure how the results would generalized to milder autism spectrum disorder.