Olga Wolke, MD

Abstract

OBJECTIVE: White matter alterations are frequently reported in autism spectrum disorder (ASD), yet the etiology is currently unknown. The objective of this investigation was to examine, for the first time, the impact of genetic and environmental factors on white matter microstructure in twins with ASD compared to control twins without ASD.METHOD: Diffusion-weighted MRIs were obtained from same-sex twin pairs (aged 6-15 years) in which at least one twin was diagnosed with ASD or neither twin exhibited a history of neurological or psychiatric disorders. Fractional anisotropy (FA) and mean diffusivity (MD) were examined across different white matter tracts in the brain and statistical and twin modeling were completed to assess the proportion of variation associated with additive genetic (A) and common/shared (C) or unique (E) environmental factors. We also developed a new version of the twin-pair difference score analysis method that estimates the contribution of genetic and environmental factors to shared covariance between different brain and behavioral traits.RESULTS: Good quality data were available from 84 twin pairs, 50 ASD pairs [32 concordant for ASD (16 monozygotic; 16 dizygotic), 16 discordant for ASD (3 monozygotic; 13 dizygotic), and 2 pairs in which one twin had ASD and the other exhibited some subthreshold symptoms (1 monozygotic; 1 dizygotic)] and 34 control pairs (20 monozygotic; 14 dizygotic). Average FA and MD across the brain, respectively, were primarily genetically mediated in both control twins (A=0.80 [0.57,1.02]; A=0.80 [0.55,1.04]) and twins concordant for having ASD (A=0.71 [0.33,1.09]; A= 0.84 [0.32,1.36]). However, there were also significant tract-specific differences between groups. For instance, genetic effects on commissural fibers were primarily associated with differences in general cognitive abilities and perhaps some diagnostic differences for ASD, e.g., our new twin-pair difference-scores analysis indicated that genetic factors may have contributed to 40-50% of the covariation between IQ scores and FA of the corpus callosum. Conversely, the increased impact of environmental factors on some projection and association fibers were primarily associated with differences in symptom severity in twins with ASD, e.g., twin-pair difference-scores suggested that unique environmental factors may have contributed to 10-20% of the covariation between autism-related symptom severity and FA of the cerebellar peduncles and external capsule.CONCLUSION: White matter alterations in youth with ASD are associated with both genetic contributions and potentially increased vulnerability or responsivity to environmental influences.DIVERSITY & INCLUSION STATEMENT: We worked to ensure sex and gender balance in the recruitment of human participants. We worked to ensure race, ethnic, and/or other types of diversity in the recruitment of human participants. We worked to ensure that the study questionnaires were prepared in an inclusive way. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented racial and/or ethnic groups in science. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented sexual and/or gender groups in science. One or more of the authors of this paper self-identifies as living with a disability. The author list of this paper includes contributors from the location and/or community where the research was conducted who participated in the data collection, design, analysis, and/or interpretation of the work.

View details for DOI 10.1016/j.jaac.2023.05.030

View details for PubMedID 37406770

View details for Web of Science ID 000783167500111

View details for DOI 10.1007/s40140-021-00484-z

View details for Web of Science ID 000738478500002

View details for DOI 10.1007/s40140-021-00482-1

View details for Web of Science ID 000706552300001

View details for DOI 10.1038/s41380-018-0330-z

View details for Web of Science ID 000572540100029

Abstract

Corticostriatal circuits (CSC) have been implicated in the presentation of some restricted and repetitive behaviours (RRBs) in children with autism-spectrum disorder (ASD), and preliminary evidence suggests that disruptions in these pathways may be associated with differences in genetic and environmental influences on brain development. The objective of this investigation was to examine the impact of genetic and environmental factors on CSC regions in twins with and without ASD and to evaluate their relationship with the severity of RRBs.We obtained T1-weighted MRIs from same-sex monozygotic and dizygotic twin pairs, aged 615 years. Good-quality data were available from 48 ASD pairs (n = 96 twins; 30 pairs concordant for ASD, 15 monozygotic and 15 dizygotic; 18 pairs discordant for ASD, 4 monozygotic and 14 dizygotic) and 34 typically developing control pairs (n = 68 twins; 20 monozygotic and 14 dizygotic pairs). We generated structural measures of the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), caudate, putamen, pallidum and thalamus using FreeSurfer. Twin pair comparisons included intraclass correlation analyses and ACE modelling (a2 = additive genetics; c2 = common or shared environment; e2 = unique or nonshared environment). We also assessed correlations with RRB severity.Structural variation in CSC regions was predominantly genetically mediated in typically developing twins (a2 = 0.56 to 0.87), except for ACC white matter volume (a2 = 0.42, 95% confidence interval [CI] 0.08 to 0.77). We also observed similar magnitudes of genetic influence in twins with ASD (a2 = 0.65 to 0.97), but the cortical thickness of the ACC (c2 = 0.44, 95% CI 0.22 to 0.66) and OFC (c2 = 0.60, 95% CI 0.25 to 0.95) was primarily associated with environmental factors in only twins with ASD. Twin pair differences in OFC grey matter volume were also correlated with RRB severity and were predominantly environmentally mediated.We obtained MRIs on 2 scanners, and analytical approaches could not identify specific genetic and environmental factors.Genetic factors primarily contribute to structural variation in subcortical CSC regions, regardless of ASD, but environmental factors may exert a greater influence on the development of grey matter thickness in the OFC and ACC in children with ASD. The increased vulnerability of OFC grey matter to environmental influences may also mediate some heterogeneity in RRB severity in children with ASD.

View details for DOI 10.1503/jpn.190030

View details for PubMedID 31603639

Abstract

Atypical growth patterns of the brain have been previously reported in autism spectrum disorder (ASD) but these alterations are heterogeneous across individuals, which may be associated with the variable effects of genetic and environmental influences on brain development. Monozygotic (MZ) and dizygotic (DZ) twin pairs with and without ASD (aged 6-15 years) were recruited to participate in this study. T1-weighted MRIs (n=164) were processed with FreeSurfer to evaluate structural brain measures. Intra-class correlations were examined within twin pairs and compared across diagnostic groups. ACE modeling was also completed. Structural brain measures, including cerebral and cerebellar gray matter (GM) and white matter (WM) volume, surface area, and cortical thickness, were primarily influenced by genetic factors in TD twins; however, mean curvature appeared to be primarily influenced by environmental factors. Similarly, genetic factors accounted for the majority of variation in brain size in twins with ASD, potentially to a larger extent regarding curvature and subcortical GM; however, there were also more environmental contributions in twins with ASD on some structural brain measures, such that cortical thickness and cerebellar WM volume were primarily influenced by environmental factors. These findings indicate potential neurobiological outcomes of the genetic and environmental risk factors that have been previously associated with ASD and, although preliminary, may help account for some of the previously outlined neurobiological heterogeneity across affected individuals. This is especially relevant regarding the role of genetic and environmental factors in the development of ASD, in which certain brain structures may be more sensitive to specific influences.

View details for PubMedID 30659287

View details for DOI 10.1503/jpn.190030

Abstract

This investigation examined whether the variation of cerebral structure is associated with genetic or environmental factors in children with autism spectrum disorder (ASD) compared with typically developing (TD) controls. T1-weighted magnetic resonance imaging scans were obtained from twin pairs (aged 6-15years) in which at least one twin was diagnosed with ASD or both were TD. Good quality data were available from 30 ASD, 18 discordant, and 34 TD pairs (n=164). Structural measures (volume, cortical thickness, and surface area) were generated with FreeSurfer, and ACE modeling was completed. Lobar structures were primarily genetically mediated in TD twins (a2=0.60-0.89), except thickness of the temporal (a2=0.33 [0.04, 0.63]) and occipital lobes (c2=0.61 [0.45, 0.77]). Lobar structures were also predominantly genetically mediated in twins with ASD (a2=0.70-1.00); however, thickness of the frontal (c2=0.81 [0.71, 0.92]), temporal (c2=0.77 [0.60, 0.93]), and parietal lobes (c2=0.87 [0.77, 0.97]), and frontal gray matter (GM) volume (c2=0.79 [0.63, 0.95]), were associated with environmental factors. Conversely, occipital thickness (a2=0.93 [0.75, 1.11]) did not exhibit the environmental contributions that were found in controls. Differences in GM volume were associated with social communication impairments for the frontal (r=0.52 [0.18, 0.75]), temporal (r=0.61 [0.30, 0.80]), and parietal lobes (r=0.53 [0.19, 0.76]). To our knowledge, this is the first investigation to suggest that environmental factors influence GM to a larger extent in children with ASD, especially in the frontal lobe.

View details for DOI 10.1093/cercor/bhz215

View details for PubMedID 31711118