Sample characteristics
We included a large sample of 1030 young children from the Shanghai Autism Early Developmental (SAED) Cohort [40], including 563 children diagnosed with ASD with DD/ID (3.98 ± 1.22 years, range from 1.26 to 6.93 years, 472 males), 212 children diagnosed with ASD without DD/ID (3.24 ± 1.15 years, range from 1.13 to 6.95 years, 184 males), 36 children with DD/ID only (4.42 ± 1.4 years, range from 1.26 to 6.8 years, 25 males) and 219 age-matched typically developing children (4.42 ± 1.62 years, range from 1.17 to 7 years, 107 males) as shown in Supplementary Table 1. The clinical measurements, including scores of Autism Diagnostic Observation Schedule (ADOS), Childhood Autism Rating Scale (CARS), Autism Behavior Checklist (ABC), the Infant-Junior High School Life Ability Scale (SM), and Social Responsiveness Scale (SRS), and cognitive performance, scores of Gesell Developmental Schedules (GDS) or IQ measured by Wechsler Preschool and Primary Scale of Intelligence (WPPSI) and Wechsler Intelligence Scale for Children (WIS-R), were statistically compared across the 3 diagnosis-related groups and the TD group. Specifically, we found the following: 1) the GDS or IQ scores of all 3 diagnosis groups are significantly lower than those of the TD group; 2) the GDS or IQ scores of ASD with DD/ID and DD/ID children are also significantly lower than those of ASD without DD/ID children; and 3) the two ASD groups had more severe social deficits than the TD and DD/ID groups (Bonferroni corrected, Ps < 1×10− 8). More details can be found in the Methods section and Supplementary Table 2.
Atypical GMV asymmetry deviation patterns
We calculated the structural asymmetry metric employing the Desikan–Killiany atlas [41] for all subjects. The group averaged GMV asymmetry maps for the TD and 3 atypical groups are shown in Figure S1. Consistent with previous findings, similar structural lateralization patterns were found across 3 diagnosis-related groups and TD children. The superior temporal sulcus, rostral anterior cingulate and insula showed leftwards laterality. The caudal middle frontal cortex, parahippocampal cortex, prefrontal cortex and temporal pole showed rightwards laterality.
To determine the individualized GMV asymmetry deviation value of each region for each subject, we calculated sex-specific normative age models with the Gaussian process regression (GPR) method. Specifically, we trained the GPR models of GMV asymmetry for each region of interest (ROI) based on 247 TD children with age and sex as covariates. Then, we put the GMV asymmetry and covariate variables (age and sex) of children in ASD with DD/ID, ASD without DD/ID and DD/ID only groups into the generated models and obtained individual deviation values from the distributions from TD children. For each atypical group, regions with significant abnormalities in deviation values resulting from the one-sample t test are shown in Fig. 2a (FDR corrected p < 0.05, Supplementary Table 3).
Specifically, for ASD children without DD/ID, the inferior parietal cortex and precentral cortex showed significant negative deviations, indicating more rightwards asymmetry compared with that of TD children, while the rostral middle frontal cortex showed significant positive deviations, indicating more leftwards asymmetry (FDR corrected p < 0.05). Significant negative deviations in the inferior parietal cortex and precentral cortex were also observed in ASD children with DD/ID. Moreover, ASD children with DD/ID exhibited six additional ROIs showing significant atypical asymmetry, including the fusiform and entorhinal, which had more rightwards asymmetry, and the isthmus cingulate, the bank of superior temporal sulcus, the paracentral gyrus, and the rostral anterior cingulate cortex, which had more leftwards asymmetry. Notably, no significant deviations were found in any ROIs in children with DD/ID.
In addition to testing mean values, the kurtosis of the regional deviation values across subjects within each diagnosis group was calculated to explore whether the altered distribution differed from a normal distribution. Given that the kurtosis of the normal distribution is 3, a value above the threshold of 5 indicated an abnormality threshold in the current study. As shown in Fig. 2b, the ASD without DD/ID group exhibited up to 11 regions showing extreme kurtosis (entorhinal, kurtosis = 64.391; parahippocampal cortex, kurtosis = 50.502; temporal pole, kurtosis = 41.451; fusiform, kurtosis = 31.153; frontal pole, kurtosis = 23.538; medial orbitofrontal, kurtosis = 21.533; postcentral cortex, kurtosis = 18.795; precentral cortex, kurtosis = 16.193; transverse temporal, kurtosis = 16.145), indicating that the distribution of GMV asymmetry deviations was widely altered with high individual variations across subjects within the group. For ASD children with DD/ID, the lateral occipital (kurtosis = 12.203) and temporal pole (kurtosis = 32.759) showed a changed distribution of GMV asymmetry deviations. Again, no regions in the DD/ID group showed altered kurtosis values greater than the threshold (kurtosis < 5).
To characterize the extent and distribution of structural asymmetry deviations at the systems level, the mean z values (normalized t values) and kurtosis values in Yeo’s 7 network [42] were calculated, as shown in Fig. 2c. Similar ASD common atypical network deviation patterns were found in the default mode network, ventral attention network, somatomotor network and visual network. Atypical distribution patterns were also observed in ASD children with and without DD/ID with extreme heterogeneity in limbic and visual networks.
To explore the between-group differences, we conducted a two-sample t-test between every pair of diagnosis groups (ASD with DD/ID vs. ASD without DD/ID, ASD with DD/ID vs. DD/ID, and ASD without DD/ID vs. DD/ID) and found no significant between-group differences for any region after FDR correction (p < 0.05). Additionally, we found significant spatial correlations of GMV asymmetry deviations between the ASD with DD/ID vs. ASD without DD/ID groups (r = 0.557, permuted p = 0.0007), and between the ASD with DD/ID vs. DD/ID groups (r = 0.741, permuted p < 0.0001), as shown in Fig. 3a.
Through unsupervised clustering algorithms, we also found that these diagnosis groups cannot be separated in terms of GMV asymmetry patterns. Through the k-means method, we calculated the distance ratio, as summed distances between-clusters divided by the summed distances within clusters, with the number of clusters from 2 to 20 and found no peak point as shown in Fig. 3.b, indicating that children with different diagnosis cannot be distinguished by multivariate GMV asymmetry deviations. The spatial visualization by individual two-dimensional vectors reduced from 34-dimensional vectors via t-SNE also confirmed that children in the groups ASD with DD/ID, ASD without DD/ID and DD cannot be differentiated from each other.
Associations between atypical asymmetry deviations and clinical symptoms
To understand the multiscale cascade in both the ASD and DD/ID populations, we conducted a canonical correlation analysis to explore the associations between brain structural asymmetry deviations and behavioural scores for ASD children without DD/ID, and ASD children with DD/ID respectively. For ASD children without DD/ID, GMV asymmetry deviations showed significant multivariate associations with clinical scores in one mode (r = 0.977, p perm = 0.033). Six ROIs (paracentral, loading = 0.361; parahippocampal, loading = 0.295; inferior frontal gyrus pars opercularis, loading = 0.269; entorhinal, loading = 0.261; frontal pole, loading = 0.211; precentral, loading = 0.201) with positive loadings and four ROIs (caudal anterior cingulate, loading = -0.376; inferior temporal gyrus, loading = -0.293; rostral middle frontal gyrus, loading = -0.255; cuneus, loading = -0.201) with negative loadings contributed to the identified canonical mode (threshold of loading = ± 0.2). Visual responsiveness (loading = 0.444), ADOS_2 (loading = 0.278), the sum of ADOS_1 and ADOS_2 (loading = 0.247), verbal communication (loading = 0.227), interaction (loading = 0.214), and independent living (loading = 0.212) scores showed positive contributions while intellectual consistency showed negative contributions (loading = -0.229) to the mode, as shown in Fig. 4. Here, positive canonical loading indicates increasing neuropsychological scores with leftwards GMV asymmetry deviations.
For ASD children with DD/ID, GMV asymmetry deviations were identified in one significant canonical mode (r = 0.988, p perm = 0.003) linking clinical scores and IQ scores. Eight ROIs (parahippocampal, loading = 0.405; posterior cingulate, loading = 0.369; lateral orbitofrontal, loading = 0.362; lingual, loading = 0.337; entorhinal, loading = 0.328; temporal pole, loading = 0.275; supramarginal, loading = 0.228; frontal pole, loading = 0.2) positively contributed to the identified mode. The superior parietal cortex was found to negatively contribute to the mode (loading = -0.325). In the linked clinical and IQ performance, intellectual consistency (loading = 0.303), self-management (loading = 0.247), interaction (loading = 0.222), verbal IQ (loading = 0.209) and Operation (loading = 0.2) showed positive contributions, while affect (loading = -0.46), social communication (loading = -0.299), CARS (loading = -0.295), activity level (loading = -0.272), social cognition (loading = -0.252), SRS (loading = -0.243), relation to object (loading = -0.22) and the use of body (loading = -0.2) showed negative contributions.
The canonical correlation analysis for ASD children with and without DD/ID did not yield any significant modes.
Association between atypical asymmetry deviations and gene expression profiles
To quantify the multivariate association pattern between genes and the brain, we conducted a partial least squares regression and identified the regression components between gene expression profiles and GMV asymmetry deviations for each group. For the ASD with DD/ID group, regression component one explained 20.6% of the response variables (r = 0.454, p = 0.007), regression component two explained 14.7% of the response variables (r = 0.384, p = 0.025) and regression component three explained 16% of the response variables (r = 0.4, p = 0.019). For the ASD without DD/ID group, regression component one did not significantly explain the response variables (r = 0.335, p = 0.053), regression component two explained 26.4% of the response variables (r = 0.39, p = 0.023), and regression component three explained 42.6% of the response variables (r = 0.402, p = 0.018). However, none of these correlations survived the spatial permutation tests (N = 10000, all \({p}_{perm}s\) >0.5). Given that genes served as source factors, these results suggest that the association pattern between the gene expression profile and GMV asymmetry was not linear.
Next, inter-regional similarity analysis was conducted to detect significant associations between gene expression profiles and GMV asymmetry deviations for each diagnosis group, as shown in Fig. 5a (for ASD children with DD/ID, r = 0.16, \({p}_{perm}\) = 0.0001; for ASD children without DD/ID, r = 0.216, \({p}_{perm}\) = 0; for DD/ID children, r = 0.241, \({p}_{perm}\) = 0). The GCI values of autism related genes and intellectual disability related genes according to the In Situ Hybridization gene lists were extracted. A significant negative correlation was found between the GCI values of intellectual disability related genes between the DD/ID and ASD without DD/ID groups (r = -0.638, p < 0.001), as shown in Fig. 5b.
The shared and specific genes and their terms from the 3 diagnosis groups are shown in a circle network in Fig. 6.a. For multigene list meta-analysis, the functional terms or pathways provide more information as shown in Fig. 6b. We found four Gene Ontology (GO) terms of GMV asymmetry-related genes (‘regulation of transmembrane transport’, ‘neuron projection development’, ‘axon’, ‘supramolecular fiber organization’), that were consistent across ASD with DD/ID, ASD without DD/ID and DD/ID groups with FDR corrected p < 0.05. The GO term clusters specifically identified in ASD children with and without DD/ID were ‘postsynapse’ and ‘brain development’. The GO terms ‘cytoplasmic translation’ and ‘polymeric cytoskeletal fiber’ were clustered together in the ASD with DD/ID and DD/ID groups. Furthermore, the ASD without DD/ID group exhibited many specific Go terms, including ‘nuclear inner membrane’, ‘synapse organization’, ‘regulation of synapse pruning’, ‘response to salt’, ‘cytoplasmic side of membrane’, ‘kinase binding’ and ‘perinuclear region of cytoplasm’, that were enriched for the expression of specific genes associated with GMV asymmetry. The GO terms of ASD with DD/ID specific genes were ‘regulation of neurotransmitter levels’, while those of DD/ID were ‘cell adhesion molecule binding’, ‘cell projection assembly’, and ‘regionalization’. To illustrate these findings, Fig. 6c shows the proportion of each diagnosis group relating to the enriched GO term clusters, and Fig. 6d shows the GO terms colored by cluster.