Abstract
Inconsistencies across studies investigating subcortical correlates of autism spectrum disorder (ASD) may stem from small sample size, sample heterogeneity, and omitting or linearly adjusting for total brain volume (TBV). To properly adjust for TBV, brain allometry—the nonlinear scaling relationship between regional volumes and TBV—was considered when examining subcortical volumetric differences between typically developing (TD) and ASD individuals. Autism Brain Imaging Data Exchange I (ABIDE I; N = 654) data was analyzed with two methodological approaches: univariate linear mixed effects models and multivariate multiple group confirmatory factor analyses. Analyses were conducted on the entire sample and in subsamples based on age, sex, and full scale intelligence quotient (FSIQ). A similar ABIDE I study was replicated and the impact of different TBV adjustments on neuroanatomical group differences was investigated. No robust subcortical allometric or volumetric group differences were observed in the entire sample across methods. Exploratory analyses suggested that allometric scaling and volume group differences may exist in certain subgroups defined by age, sex, and/or FSIQ. The type of TBV adjustment influenced some reported volumetric and scaling group differences. This study supports the absence of robust volumetric differences between ASD and TD individuals in the investigated volumes when adjusting for brain allometry, expands the literature by finding no group difference in allometric scaling, and further suggests that differing TBV adjustments contribute to the variability of reported neuroanatomical differences in ASD.
Highlights
Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by early persistent deficits in social communication and interactions and restricted, repetitive patterns of behavior, interests, or activities
Considering that neuroanatomical markers within the brain are more closely associated to symptoms of a condition, the present study investigated neuroanatomical differences in the Autism Brain Imaging Data Exchange I (ABIDE I, Di Martino et al, 2014; N = 1,112) between ASD and typically developing (TD) individuals in terms of their regional volumes and the scaling relationship between their regional volumes and total brain volume (TBV; sum of total gray matter (GM) and white matter (WM))
Since there is currently no rule of thumb for the cutoff values of fit indices that should be employed in varying conditions, leaving researchers to choose fit criteria (Putnick & Bornstein, 2016), we considered there to be a neuroanatomical group difference even if Chen's (2007) criteria indicated invariance, if (a) the χ2 difference test was significant, (b) the multiple group confirmatory factor analysis (MGCFA) effect size was greater than 0.2, (c) the corresponding linear mixed effects models (LMEMs) effect size was similar to the MGCFA effect size, and (d) the corresponding LMEM with False Discovery Rate correction (FDR) was significant with and without outliers
Summary
Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by early persistent deficits in social communication and interactions and restricted, repetitive patterns of behavior, interests, or activities. These symptoms impair social or occupational functioning and are not restricted to a developmental delay or intellectual deficiencies (American Psychiatric Association, 2013). Considering that neuroanatomical markers within the brain are more closely associated to symptoms of a condition, the present study investigated neuroanatomical differences in the Autism Brain Imaging Data Exchange I (ABIDE I, Di Martino et al, 2014; N = 1,112) between ASD and typically developing (TD) individuals in terms of their regional (i.e., subcortical and cortical) volumes and the scaling relationship between their regional volumes and total brain volume (TBV; sum of total gray matter (GM) and white matter (WM))
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