Prediction of Intellectual Impairment By Developmental Assesments in Children with Autism Spectrum Disorder Compared to Globally Delayed Children

Background:     Significant global developmental delay (GD) as assed below age three,  is considered a preliminary marker of intellectual disability (ID). However, the trajectory of the gap may be different in children diagnosed of Autism Spectrum Disorder (ASD) as compared to children with delays without ASD diagnosis. 

Objectives: To evaluate to trajectory of developmental delay in children with ASD and in children with GD without ASD.

Specific aim: to compare developmental assessment tools to subsequently performed cognitive test results in a population with ASD as compared to GD children.  

Methods: Children (n=88) diagnosed with global developmental delay (delay of more than 2 SD in two or more areas of development), and assessed with Bayley 2 developmental test, were followed and reassessed after age four using cognitive tests (WIPPSI, Kaufman and WISC-R). They were divided in two groups according to definite diagnosis of ASD (n= 38, 26 males) or GD without ASD (n=50, 37 males).

Results: As expected, a positive correlation was found between lesser degree of developmental delay as measured by MDI and subsequent IQ, in both groups. From ASD group, 60.1% scored with significant delayed performance on developmental test and 66% from GD group without ASD were significantly delayed. Subsequently, on cognitive tests after age 4 years, 20% of the non-ASD GD group scored with an IQ less than 70 and 28.9% from ASD group scored with comorbid intellectual disability.

Conclusions: MDI score less that 65 on Bayley 2 performed before age 3 years, predicts lower IQ (less than 70), on subsequent cognitive assessments. However, developmental delay trajectory is more stable in ASD group than in globally delayed children.