The importance of low IQ to early diagnosis of autism

Abstract

Some individuals can flexibly adapt to life's changing demands while others, in particular those with Autism Spectrum Disorder (ASD), find it challenging. The origin of early individual differences in cognitive abilities, the putative tools with which to navigate novel information in life, including in infants later diagnosed with ASD remains unexplored. Moreover, the role of intelligence quotient (IQ) vis-à-vis core features of autism remains debated. We systematically investigate the contribution of early IQ in future autism outcomes in an extremely large, population-based study of 8000 newborns, infants, and toddlers from the US between 2 and 68 months with over 15,000 cross-sectional and longitudinal assessments, and for whom autism outcomes are ascertained or ruled out by about 2-4 years. This population is representative of subjects involved in the National Institutes of Health (NIH)-funded research, mainly on atypical development, in the US. Analyses using predetermined age bins showed that IQ scores are consistently lower in ASD relative to typically developing (TD) children at all ages (p < 0.001), and IQ significantly correlates with social, non-social, and total Calibrated Severity Scores (CSS) on the Autism Diagnostic Observation Schedule (ADOS) (p<0.01). Lower IQ is associated with greater autistic impairments. Note, verbal IQ (VIQ) is no better than the full-scale IQ to predict ASD cases. These findings raise new, compelling questions about potential atypical brain circuitry affecting performance in both verbal and nonverbal abilities and preceding an ASD diagnosis. This study is the first to establish prospectively that low early IQ is a major feature of ASD in early childhood. Lay SummaryThe role of IQ scores in autism remains debated. We systematically investigate the contribution of early IQ in an extremely large study of 8,000 children between 2 and 68 months with autism outcomes by about 2-4 years. We show that IQ scores are consistently lower in ASD relative to TD children. This study is the first to establish prospectively that low early IQ is a predictor for ASD diagnosis in early childhood.

Intellectual development in young children with autism spectrum disorders: A longitudinal study

“…Regarding PIQ development, the results from the autistic group were heterogeneous, since PIQ significantly deteriorated for 16 children (Cluster 2), while mildly improving for 23 children (Clusters 1 and 3). The observed PIQ drop in Cluster 2 seems to be in line with Denisova and Lin's (2023) large‐scale longitudinal study that found an extremely rapid decline in PIQ in 10‐ to 70‐month‐old autistic children relative to TD children. The fact that the current study found either a decline or a mild rise in PIQ scores across the three clusters longitudinally, but no signs of considerable improvement—at least not of the size of the improvement that autistic children in Cluster 1 exhibited in their VIQ scores, implies that the developmental progress in autistic children's visuospatial abilities was rather limited.…”

“…Although not a core symptom in autism, intellectual functioning atypicalities are observed in autism since infancy (Bryson et al, 2007;Denisova & Lin, 2023). The existing literature on IQ measurements shows that autistic children tend to demonstrate a discrepancy between verbal and nonverbal intellectual abilities, indicating an atypical pattern of verbal and performance IQ differences (Ankenman et al, 2014;Black et al, 2009;Giofrè et al, 2019;Mayes & Calhoun, 2008;Nader et al, 2015Nader et al, , 2016.…”

“…Up until today, very little is known about autistic individuals' PIQ and VIQ trajectories longitudinally. Denisova and Lin's (2023) largest so far longitudinal assessment of IQ data obtained from autistic and typically developing (TD) children at multiple time-points at very early ages (specifically, at 6, 12, 18, 24, 30, and 36 months) has shown that low IQ (as compared to TD peers) is a hallmark feature of autism in early-diagnosed children, thus, it can be considered a potential marker of future autism diagnosis. Crucially, the same researchers have reported a more rapid and steeper decline in PIQ in the autistic group relative to TD group, which begins around 40 months, in contrast to the autistic children's VIQ which has been found to be relatively more unaffected over time.…”

Copy-number variants and polygenic risk for intelligence confer risk for autism spectrum disorder irrespective of their effects on cognitive ability

“…Low cognitive ability is a major feature of ASD and is associated with greater autistic impairments ( 44 ). We find that intolerant deletions and duplications follow this pattern, such that they decrease cognitive ability and increase ASD risk.…”

Neurobiology of cognitive abilities in early childhood autism

“…This perspective considers complexities in the relationship between IQ and autism diagnosis within a novel maturational framework (Figure 1). First, we clarify the neurobiological and genetic evidence that may explain the co-occurrence between ASD and Intellectual Disability (ID) (Maenner et al, 2023;Shaw et al, 2023) and lower IQs (Denisova & Lin, 2022), including the possibility that high IQ may "rescue" the social communication impairments. Second, we consider the important role of critical periods during growth and development, how impairment of transient processes during these critical developmental windows may interact with ASD risk genes, and how these, taken together, may contribute to some early-diagnosed ASD cases that also have lower IQ very early in infancy.…”