Evidence for dysregulation of axonal growth and guidance in the etiology of ASD

Inferior Frontal Gyrus Volume Loss Distinguishes Between Autism and (Comorbid) Attention-Deficit/Hyperactivity Disorder-A FreeSurfer Analysis in Children

Objective: Autism spectrum (ASD) and attention-deficit/hyperactivity disorder (ADHD) are neurodevelopmental disorders with a high rate of comorbidity. To date, diagnosis is based on clinical presentation and distinct reliable biomarkers have been identified neither for ASD nor ADHD. Most previous neuroimaging studies investigated ASD and ADHD separately. Method: To address the question of structural brain differences between ASD and ADHD, we performed FreeSurfer analysis in a sample of children with ADHD (n = 30), with high-functioning ASD (n = 14), with comorbid high-functioning ASD and ADHD (n = 15), and of typically developed controls (TD; n = 36). With FreeSurfer, an automated brain imaging processing and analyzing suite, we reconstructed the cerebral cortex and calculated gray matter volumes as well as cortical surface parameters in terms of cortical thickness and mean curvature. Results: A significant main effect of the factor ADHD was detected for the left inferior frontal gyrus (Pars orbitalis) volume, with the ADHD group exhibiting smaller Pars orbitalis volumes. Dimensional measures of autism (SRS total raw score) and ADHD (DISYPS-II FBB-ADHD score) had no significant influence on the left Pars orbitalis volume. Both, ASD and ADHD tended to have an effect on cortical thickness or mean curvature, which did not survive correction for multiple comparisons. Conclusion: Our results underline that ADHD rather than ASD is associated with volume loss in the left inferior frontal gyrus (Pars orbitalis). This area might play a relevant role in modulating symptoms of inattention and/or impulsivity in ADHD. The effect of comorbid ADHD in ASD samples and vice versa, on cortical thickness and mean curvature, requires further investigation in larger samples.

Spatiotemporal Relationship of Brain Pathways during Human Fetal Development Using High-Angular Resolution Diffusion MR Imaging and Histology

In this study, we aimed to identify major fiber pathways and their spatiotemporal relationships within transient fetal zones in the human fetal brain by comparing postmortem high-angular resolution diffusion MR imaging (HARDI) in combination with deterministic streamline tractography and histology. Diffusion weighted imaging was performed on postmortem human fetal brains [N = 9, age = 18–34 post-conceptual weeks (PCW)] that were grossly normal with no pathologic abnormalities. After HARDI was performed, the fibers were reconstructed using Q-ball algorithm and deterministic streamline tractography. The position of major fiber pathways within transient fetal zones was identified both on diffusion weighted images and on histological sections. Our major findings include: (1) the development of massive projection fibers by 18 PCW, as compared to most association fibers (with the exception of limbic fibers) which have only begun to emerge, (2) the characteristic laminar distribution and sagittal plane geometry of reconstructed fibers throughout development, (3) the protracted prenatal development shown of the corpus collosum and its' associated fibers, as well as the association fibers, and (4) the predomination of radial coherence in the telencephalon (i.e., majority of streamlines in the telencephalic wall were radially oriented) during early prenatal period (24 PCW). In conclusion, correlation between histology and HARDI (in combination with Q-ball reconstruction and deterministic streamline tractography) allowed us to detect sequential development of fiber systems (projection, callosal, and association), their spatial relations with transient fetal zones, and their geometric properties.

Endocannabinod Signal Dysregulation in Autism Spectrum Disorders: A Correlation Link between Inflammatory State and Neuro-Immune Alterations

Several studies highlight a key involvement of endocannabinoid (EC) system in autism pathophysiology. The EC system is a complex network of lipid signaling pathways comprised of arachidonic acid-derived compounds (anandamide, AEA) and 2-arachidonoyl glycerol (2-AG), their G-protein-coupled receptors (cannabinoid receptors CB1 and CB2) and the associated enzymes. In addition to autism, the EC system is also involved in several other psychiatric disorders (i.e., anxiety, major depression, bipolar disorder and schizophrenia). This system is a key regulator of metabolic and cellular pathways involved in autism, such as food intake, energy metabolism and immune system control. Early studies in autism animal models have demonstrated alterations in the brain's EC system. Autism is also characterized by immune system dysregulation. This alteration includes differential monocyte and macrophage responses, and abnormal cytokine and T cell levels. EC system dysfunction in a monocyte and macrophagic cellular model of autism has been demonstrated by showing that the mRNA and protein for CB2 receptor and EC enzymes were significantly dysregulated, further indicating the involvement of the EC system in autism-associated immunological disruptions. Taken together, these new findings offer a novel perspective in autism research and indicate that the EC system could represent a novel target option for autism pharmacotherapy.

Neuronal Polarity in the Embryonic Mammalian Cerebral Cortex

The cerebral cortex is composed of billions of neurons that can grossly be subdivided into two broad classes: inhibitory GABAergic interneurons and excitatory glutamatergic neurons. The majority of cortical neurons in mammals are the excitatory type and they are the main focus of this review article. Like many of the cells in multicellular organisms, fully differentiated neurons are both morphologically and functionally polarized. However, they go through several changes in polarity before reaching this final mature differentiated state. Neurons are derived from polarized neuronal progenitor/stem cells and their commitment to neuronal fate is decided by cellular and molecular asymmetry during their last division in the neurogenic zone. They migrate from their birthplace using so-called multipolar migration, during which they switch direction of movement several times, and repolarize for bipolar migration when the axon is specified. Therefore, neurons have to break their previous symmetry, change their morphology and adequately respond to polarizing signals during migration in order to reach the correct position in the cortex and start making connections. Finally, the dendritic tree is elaborated and the axon/dendrite morphological polarity is set. Here we will describe the function, establishment and maintenance of polarity during the different developmental steps starting from neural stem cell (NSC) division, neuronal migration and axon specification at embryonic developmental stages.

Altered white matter integrity in adults with autism spectrum disorder and an IQ >100: a diffusion tensor imaging study

OBJECTIVE

White matter (WM) alterations have been reported in children and adults with autism spectrum disorder (ASD). In particular, impaired connectivity of limbic structures may be related to social deficits. Heterogeneous findings could be explained in terms of differences in sample characteristics and methodology. In this context, non-syndromic forms might differ substantially in WM structure from secondary ASD forms.

METHOD

In an attempt to recruit a homogeneous study sample, we included adults with high-functioning ASD and an IQ > 100 to decrease the influence of syndromic forms being often associated with cognitive deficits. Diffusion tensor imaging (DTI) was performed in 30 participants with ASD and 30 pairwise-matched controls. Fractional anisotropy (FA) and mean diffusivity (MD) as surrogate imaging markers for WM integrity were calculated.

RESULTS

We found a significant FA decrease in the ASD group in the genu and body of the corpus callosum (CC). Increased MD was detected in the subgenual anterior cingulate cortex (sACC).

CONCLUSION

The finding of decreased WM integrity in the genu of the CC is in line with earlier studies reporting a decreased number of interhemispheric fibers in the frontal lobe of ASD. Alterations in the sACC might be associated with 'Theory of mind' deficits.

Is functional brain connectivity atypical in autism? A systematic review of EEG and MEG studies

BACKGROUND

Although it is well recognized that autism is associated with altered patterns of over- and under-connectivity, specifics are still a matter of debate. Little has been done so far to synthesize available literature using whole-brain electroencephalography (EEG) and magnetoencephalography (MEG) recordings.

OBJECTIVES

1) To systematically review the literature on EEG/MEG functional and effective connectivity in autism spectrum disorder (ASD), 2) to synthesize and critically appraise findings related with the hypothesis that ASD is characterized by long-range underconnectivity and local overconnectivity, and 3) to provide, based on the literature, an analysis of tentative factors that are likely to mediate association between ASD and atypical connectivity (e.g., development, topography, lateralization).

METHODS

Literature reviews were done using PubMed and PsychInfo databases. Abstracts were screened, and only relevant articles were analyzed based on the objectives of this paper. Special attention was paid to the methodological characteristics that could have created variability in outcomes reported between studies.

RESULTS

Our synthesis provides relatively strong support for long-range underconnectivity in ASD, whereas the status of local connectivity remains unclear. This observation was also mirrored by a similar relationship with lower frequencies being often associated with underconnectivity and higher frequencies being associated with both under- and over-connectivity. Putting together these observations, we propose that ASD is characterized by a general trend toward an under-expression of lower-band wide-spread integrative processes compensated by more focal, higher-frequency, locally specialized, and segregated processes. Further investigation is, however, needed to corroborate the conclusion and its generalizability across different tasks. Of note, abnormal lateralization in ASD, specifically an elevated left-over-right EEG and MEG functional connectivity ratio, has been also reported consistently across studies.

CONCLUSIONS

The large variability in study samples and methodology makes a systematic quantitative analysis (i.e. meta-analysis) of this body of research impossible. Nevertheless, a general trend supporting the hypothesis of long-range functional underconnectivity can be observed. Further research is necessary to more confidently determine the status of the hypothesis of short-range overconnectivity. Frequency-band specific patterns and their relationships with known symptoms of autism also need to be further clarified.

Semaphorin-Plexin signaling influences early ventral telencephalic development and thalamocortical axon guidance

Background

Sensory processing relies on projections from the thalamus to the neocortex being established during development. Information from different sensory modalities reaching the thalamus is segregated into specialized nuclei, whose neurons then send inputs to cognate cortical areas through topographically defined axonal connections.

Developing thalamocortical axons (TCAs) normally approach the cortex by extending through the subpallium; here, axonal navigation is aided by distributed guidance cues and discrete cell populations, such as the corridor neurons and the internal capsule (IC) guidepost cells. In mice lacking Semaphorin-6A, axons from the dorsal lateral geniculate nucleus (dLGN) bypass the IC and extend aberrantly in the ventral subpallium. The functions normally mediated by Semaphorin-6A in this system remain unknown, but might depend on interactions with Plexin-A2 and Plexin-A4, which have been implicated in other neurodevelopmental processes.

Methods

We performed immunohistochemical and neuroanatomical analyses of thalamocortical wiring and subpallial development in Sema6a and Plxna2; Plxna4 null mutant mice and analyzed the expression of these genes in relevant structures.

Results

In Plxna2; Plxna4 double mutants we discovered TCA pathfinding defects that mirrored those observed in Sema6a mutants, suggesting that Semaphorin-6A − Plexin-A2/Plexin-A4 signaling might mediate dLGN axon guidance at subpallial level.

In order to understand where and when Semaphorin-6A, Plexin-A2 and Plexin-A4 may be required for proper subpallial TCA guidance, we then characterized their spatiotemporal expression dynamics during early TCA development. We observed that the thalamic neurons whose axons are misrouted in these mutants normally express Semaphorin-6A but not Plexin-A2 or Plexin-A4. By contrast, all three proteins are expressed in corridor cells and other structures in the developing basal ganglia.

This finding could be consistent with an hypothetical action of Plexins as guidance signals through Sema6A as a receptor on dLGN axons, and/or with their indirect effect on TCA guidance due to functions in the morphogenesis of subpallial intermediate targets. In support of the latter possibility, we observed that in both Plxna2; Plxna4 and Sema6a mutants some IC guidepost cells abnormally localize in correspondence of the ventral path misrouted TCAs elongate into.

Conclusions

These findings implicate Semaphorin-6A − Plexin-A2/Plexin-A4 interactions in dLGN axon guidance and in the spatiotemporal organization of guidepost cell populations in the mammalian subpallium.

Electronic supplementary material

The online version of this article (doi:10.1186/s13064-017-0083-4) contains supplementary material, which is available to authorized users.

K+ Channel Kv3.4 Is Essential for Axon Growth by Limiting the Influx of Ca2+ into Growth Cones

Membrane excitability in the axonal growth cones of embryonic neurons influences axon growth. Voltage-gated K⁺ (Kv) channels are key factors in controlling membrane excitability, but whether they regulate axon growth remains unclear. Here, we report that Kv3.4 is expressed in the axonal growth cones of embryonic spinal commissural neurons, motoneurons, dorsal root ganglion neurons, retinal ganglion cells, and callosal projection neurons during axon growth. Our in vitro (cultured dorsal spinal neurons of chick embryos) and in vivo (developing chick spinal commissural axons and rat callosal axons) findings demonstrate that knockdown of Kv3.4 by a specific shRNA impedes axon initiation, elongation, pathfinding, and fasciculation. In cultured dorsal spinal neurons, blockade of Kv3.4 by blood depressing substance II suppresses axon growth via an increase in the amplitude and frequency of Ca²⁺ influx through T-type and L-type Ca²⁺ channels. Electrophysiological results show that Kv3.4, the major Kv channel in the axonal growth cones of embryonic dorsal spinal neurons, is activated at more hyperpolarized potentials and inactivated more slowly than it is in postnatal and adult neurons. The opening of Kv3.4 channels effectively reduces growth cone membrane excitability, thereby limiting excessive Ca²⁺ influx at subthreshold potentials or during Ca²⁺-dependent action potentials. Furthermore, excessive Ca²⁺ influx induced by an optogenetic approach also inhibits axon growth. Our findings suggest that Kv3.4 reduces growth cone membrane excitability and maintains [Ca²⁺]_i at an optimal concentration for normal axon growth.SIGNIFICANCE STATEMENT Accumulating evidence supports the idea that impairments in axon growth contribute to many clinical disorders, such as autism spectrum disorders, corpus callosum agenesis, Joubert syndrome, Kallmann syndrome, and horizontal gaze palsy with progressive scoliosis. Membrane excitability in the growth cone, which is mainly controlled by voltage-gated Ca²⁺ (Cav) and K⁺ (Kv) channels, modulates axon growth. The role of Cav channels during axon growth is well understood, but it is unclear whether Kv channels control axon outgrowth by regulating Ca²⁺ influx. This report shows that Kv3.4, which is transiently expressed in the axonal growth cones of many types of embryonic neurons, acts to reduce excessive Ca²⁺ influx through Cav channels and thus permits normal axon outgrowth.

Cortical interactions during the resolution of information processing demands in autism spectrum disorders

INTRODUCTION

Our flexible and adaptive interactions with the environment are guided by our individual representation of the physical world, estimated through sensation and evaluation of available information against prior knowledge. When linking sensory evidence with higher-level expectations for action, the central nervous system (CNS) in typically developing (TD) individuals relies in part on distributed and interacting cortical regions to communicate neuronal signals flexibly across the brain. Increasing evidence suggests that the balance between levels of signal and noise during information processing may be disrupted in individuals with Autism Spectrum Disorders (ASD).

METHODS

Participants with and without ASD performed a visuospatial interference task while undergoing functional Magnetic Resonance Imaging (fMRI). We empirically estimated parameters characterizing participants' latencies and their subtle fluctuations (noise accumulation) over the 16-min scan. We modeled hemodynamic activation and used seed-based analyses of neural coupling to study dysfunction in interference-specific connectivity in a subset of ASD participants who were nonparametrically matched to TD participants on age, male-to-female ratio, and magnitude of movement during the scan.

RESULTS

Stochastic patterns of response fluctuations reveal significantly higher noise-to-signal levels and a more random and noisy structure in ASD versus TD participants, and in particular ASD adults who have the greatest clinical autistic deficits. While individuals with ASD show an overall weaker modulation of interference-specific functional connectivity relative to TD individuals, in particular between the seeds of Anterior Cingulate Cortex (ACC) and Inferior Parietal Sulcus (IPS) and the rest of the brain, we found that in ASD, higher uncertainty during the task is linked to increased interference-specific coupling between bilateral anterior insula and prefrontal cortex.

CONCLUSIONS

Subtle and informative differences in the structure of experiencing information exist between ASD and TD individuals. Our findings reveal in ASD an atypical capacity to apply previously perceived information in a manner optimal for adaptive functioning, plausibly revealing suboptimal message-passing across the CNS.

Abnormal Development of the Earliest Cortical Circuits in a Mouse Model of Autism Spectrum Disorder

Autism spectrum disorder (ASD) involves deficits in speech and sound processing. Cortical circuit changes during early development likely contribute to such deficits. Subplate neurons (SPNs) form the earliest cortical microcircuits and are required for normal development of thalamocortical and intracortical circuits. Prenatal valproic acid (VPA) increases ASD risk, especially when present during a critical time window coinciding with SPN genesis. Using optical circuit mapping in mouse auditory cortex, we find that VPA exposure on E12 altered the functional excitatory and inhibitory connectivity of SPNs. Circuit changes manifested as "patches" of mostly increased connection probability or strength in the first postnatal week and as general hyper-connectivity after P10, shortly after ear opening. These results suggest that prenatal VPA exposure severely affects the developmental trajectory of cortical circuits and that sensory-driven activity may exacerbate earlier, subtle connectivity deficits. Our findings identify the subplate as a possible common pathophysiological substrate of deficits in ASD.

Neurexins 1-3 Each Have a Distinct Pattern of Expression in the Early Developing Human Cerebral Cortex

Neurexins (NRXNs) are presynaptic terminal proteins and candidate neurodevelopmental disorder susceptibility genes; mutations presumably upset synaptic stabilization and function. However, analysis of human cortical tissue samples by RNAseq and quantitative real-time PCR at 8-12 postconceptional weeks, prior to extensive synapse formation, showed expression of all three NRXNs as well as several potential binding partners. However, the levels of expression were not identical; NRXN1 increased with age and NRXN2 levels were consistently higher than for NRXN3. Immunohistochemistry for each NRXN also revealed different expression patterns at this stage of development. NRXN1 and NRXN3 immunoreactivity was generally strongest in the cortical plate and increased in the ventricular zone with age, but was weak in the synaptogenic presubplate (pSP) and marginal zone. On the other hand, NRXN2 colocalized with synaptophysin in neurites of the pSP, but especially with GAP43 and CASK in growing axons of the intermediate zone. Alternative splicing modifies the role of NRXNs and we found evidence by RNAseq for exon skipping at splice site 4 and concomitant expression of KHDBRS proteins which control this splicing. NRXN2 may play a part in early cortical synaptogenesis, but NRXNs could have diverse roles in development including axon guidance, and intercellular communication between proliferating cells and/or migrating neurons.

SYD-1 Promotes Multiple Developmental Steps Leading to Neuronal Connectivity

The establishment of neuronal connectivity requires precise orchestration of multiple developmental steps, including axon specification, axon guidance, selection of synaptic target sites, and development of synaptic specializations. Although these are separate developmental steps, evidence indicates that some of the signaling molecules that regulate these steps are shared. In this review, we focus on SYD-1, a RhoGAP-like protein that has been implicated in each step of axonal development. We discuss interactions between SYD-1, UNC-40(DCC) and RhoGTPases and highlight both similarities and differences in how SYD-1 functions to regulate the different steps of axonal development. These observations reveal an example of how a signaling protein can be repurposed across sequential developmental steps.

Disrupted development and imbalanced function in the global neuronal workspace: a positive-feedback mechanism for the emergence of ASD in early infancy

Autism spectrum disorder (ASD) is increasingly being conceptualized as a spectrum disorder of connectome development. We review evidence suggesting that ASD is characterized by a positive feedback loop that amplifies small functional variations in early-developing sensory-processing pathways into structural and functional imbalances in the global neuronal workspace. Using vision as an example, we discuss how early functional variants in visual processing may be feedback-amplified to produce variant object categories and disrupted top-down expectations, atypically large expectation-to-perception mismatches, problems re-identifying individual people and objects, socially inappropriate, generally aversive emotional responses and disrupted sensory-motor coordination. Viewing ASD in terms of feedback amplification of small functional variants allows a number of recent models of ASD to be integrated with neuroanatomical, neurofunctional and genetic data.

Morphological Alterations in the Thalamus, Striatum, and Pallidum in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a common neurodevelopmental disorder with cognitive, motor, and emotional symptoms. The thalamus and basal ganglia form circuits with the cortex supporting all three of these behavioral domains. Abnormalities in the structure of subcortical regions may suggest atypical development of these networks, with implications for understanding the neural basis of ASD symptoms. Findings from previous volumetric studies have been inconsistent. Here, using advanced surface-based methodology, we investigated localized differences in shape and surface area in the basal ganglia and thalamus in ASD, using T1-weighted anatomical images from the Autism Brain Imaging Data Exchange (373 male participants aged 7-35 years with ASD and 384 typically developing). We modeled effects of diagnosis, age, and their interaction on volume, shape, and surface area. In participants with ASD, we found expanded surface area in the right posterior thalamus corresponding to the pulvinar nucleus, and a more concave shape in the left mediodorsal nucleus. The shape of both caudal putamen and pallidum showed a relatively steeper increase in concavity with age in ASD. Within ASD participants, restricted, repetitive behaviors were positively associated with surface area in bilateral globus pallidus. We found no differences in overall volume, suggesting that surface-based approaches have greater sensitivity to detect localized differences in subcortical structure. This work adds to a growing body of literature implicating corticobasal ganglia-thalamic circuits in the pathophysiology of ASD. These circuits subserve a range of cognitive, emotional, and motor functions, and may have a broad role in the complex symptom profile in ASD.

Age-related differences in autism: The case of white matter microstructure

Autism spectrum disorder (ASD) is typified as a brain connectivity disorder in which white matter abnormalities are already present early on in life. However, it is unknown if and to which extent these abnormalities are hard-wired in (older) adults with ASD and how this interacts with age-related white matter changes as observed in typical aging. The aim of this first cross-sectional study in mid- and late-aged adults with ASD was to characterize white matter microstructure and its relationship with age. We utilized diffusion tensor imaging with head motion control in 48 adults with ASD and 48 age-matched controls (30-74 years), who also completed a Flanker task. Intra-individual variability of reaction times (IIVRT) measures based on performance on the Flanker interference task were used to assess IIVRT-white matter microstructure associations. We observed primarily higher mean and radial diffusivity in white matter microstructure in ASD, particularly in long-range fibers, which persisted after taking head motion into account. Importantly, group-by-age interactions revealed higher age-related mean and radial diffusivity in ASD, in projection and association fiber tracts. Subtle dissociations were observed in IIVRT-white matter microstructure relations between groups, with the IIVRT-white matter association pattern in ASD resembling observations in cognitive aging. The observed white matter microstructure differences are lending support to the structural underconnectivity hypothesis in ASD. These reductions seem to have behavioral percussions given the atypical relationship with IIVRT. Taken together, the current results may indicate different age-related patterns of white matter microstructure in adults with ASD. Hum Brain Mapp 38:82-96, 2017. © 2016 Wiley Periodicals, Inc.

Support vector machine model of developmental brain gene expression data for prioritization of Autism risk gene candidates

MOTIVATION

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders with clinical heterogeneity and a substantial polygenic component. High-throughput methods for ASD risk gene identification produce numerous candidate genes that are time-consuming and expensive to validate. Prioritization methods can identify high-confidence candidates. Previous ASD gene prioritization methods have focused on a priori knowledge, which excludes genes with little functional annotation or no protein product such as long non-coding RNAs (lncRNAs).

RESULTS

We have developed a support vector machine (SVM) model, trained using brain developmental gene expression data, for the classification and prioritization of ASD risk genes. The selected feature model had a mean accuracy of 76.7%, mean specificity of 77.2% and mean sensitivity of 74.4%. Gene lists comprised of an ASD risk gene and adjacent genes were ranked using the model's decision function output. The known ASD risk genes were ranked on average in the 77.4th, 78.4th and 80.7th percentile for sets of 101, 201 and 401 genes respectively. Of 10,840 lncRNA genes, 63 were classified as ASD-associated candidates with a confidence greater than 0.95. Genes previously associated with brain development and neurodevelopmental disorders were prioritized highly within the lncRNA gene list.

CONTACT

liangjw@clemson.eduSupplementary information: Supplementary data are available at Bioinformatics online.

Impaired Neurite Contact Guidance in Ubiquitin Ligase E3a (Ube3a)-Deficient Hippocampal Neurons on Nanostructured Substrates

Recent discoveries indicate that during neuronal development the signaling processes that regulate extracellular sensing (e.g., adhesion, cytoskeletal dynamics) are important targets for ubiquitination-dependent regulation, in particular through E3 ubiquitin ligases. Among these, Ubiquitin E3a ligase (UBE3A) has a key role in brain functioning, but its function and how its deficiency results in the neurodevelopmental disorder Angelman syndrome is still unclear. Here, the role of UBE3A is investigated in neurite contact guidance during neuronal development, in vitro. The microtopography sensing of wild-type and Ube3a-deficient hippocampal neurons is studied by exploiting gratings with different topographical characteristics, with the aim to compare their capabilities to read and follow physical directional stimuli. It is shown that neuronal contact guidance is defective in Ube3a-deficient neurons, and this behavior is linked to an impaired activation of the focal adhesion signaling pathway. Taken together, the results suggest that the neuronal contact sensing machinery might be affected in Angelman syndrome.

Acetaminophen Use for Fever in Children Associated with Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is characterized by persistent deficits in social communication and restrictive behavior, interests, and activities. Our previous case-control study showed that use of acetaminophen at age 12-18 months is associated with increased likelihood for ASD (OR 8.37, 95% CI 2.08-33.7). In this study, we again show that acetaminophen use is associated with ASD (p = 0.013). Because these children are older than in our first study, the association is reversed; fewer children with ASD vs. non-ASD children use acetaminophen as a "first choice" compared to "never use" (OR 0.165, 95% CI 0.045, 0.599). We found significantly more children with ASD vs. non- ASD children change to the use of ibuprofen when acetaminophen is not effective at reducing fever (p = 0.033) and theorize this change in use is due to endocannabinoid system dysfunction. We also found that children with ASD vs. non-ASD children are significantly more likely to show an increase in sociability when they have a fever (p = 0.037) and theorize that this increase is due to anandamide activation of the endocannabinoid system in ASD children with low endocannabinoid tone from early acetaminophen use. In light of this we recommend that acetaminophen use be reviewed for safety in children.

White Matter Neurons in Young Adult and Aged Rhesus Monkey

In humans and non-human primates (NHP), white matter neurons (WMNs) persist beyond early development. Their functional importance is largely unknown, but they have both corticothalamic and corticocortical connectivity and at least one subpopulation has been implicated in vascular regulation and sleep. Several other studies have reported that the density of WMNs in humans is altered in neuropathological or psychiatric conditions. The present investigation evaluates and compares the density of superficial and deep WMNs in frontal (FR), temporal (TE), and parietal (Par) association regions of four young adult and four aged male rhesus monkeys. A major aim was to determine whether there was age-related neuronal loss, as might be expected given the substantial age-related changes known to occur in the surrounding white matter environment. Neurons were visualized by immunocytochemistry for Neu-N in coronal tissue sections (30 μm thickness), and neuronal density was assessed by systematic random sampling. Per 0.16 mm² sampling box, this yielded about 40 neurons in the superficial WM and 10 in the deep WM. Consistent with multiple studies of cell density in the cortical gray matter of normal brains, neither the superficial nor deep WM populations showed statistically significant age-related neuronal loss, although we observed a moderate decrease with age for the deep WMNs in the frontal region. Morphometric analyses, in contrast, showed significant age effects in soma size and circularity. In specific, superficial WMNs were larger in FR and Par WM regions of the young monkeys; but in the TE, these were larger in the older monkeys. An age effect was also observed for soma circularity: superficial WMNs were more circular in FR and Par of the older monkeys. This second, morphometric result raises the question of whether other age-related morphological, connectivity, or molecular changes occur in the WMNs. These could have multiple impacts, given the wide range of putative WMN functions and their involvement in both corticothalamic and corticocortical circuitry.

Drosophila Homolog of Human KIF22 at the Autism-Linked 16p11.2 Loci Influences Synaptic Connectivity at Larval Neuromuscular Junctions

Copy number variations at multiple chromosomal loci, including 16p11.2, have recently been implicated in the pathogenesis of autism spectrum disorder (ASD), a neurodevelopmental disease that affects 1~3% of children worldwide. The aim of this study was to investigate the roles of human genes at the 16p11.2 loci in synaptic development using Drosophila larval neuromuscular junctions (NMJ), a well-established model synapse with stereotypic innervation patterns. We conducted a preliminary genetic screen based on RNA interference in combination with the GAL4-UAS system, followed by mutational analyses. Our result indicated that disruption of klp68D, a gene closely related to human KIF22, caused ectopic innervations of axon branches forming type III boutons in muscle 13, along with less frequent re-routing of other axon branches. In addition, mutations in klp64D, of which gene product forms Kinesin-2 complex with KLP68D, led to similar targeting errors of type III axons. Mutant phenotypes were at least partially reproduced by knockdown of each gene via RNA interference. Taken together, our data suggest the roles of Kinesin-2 proteins, including KLP68D and KLP64D, in ensuring proper synaptic wiring.

Does Rubella Cause Autism: A 2015 Reappraisal?

In the 1970s, Stella Chess found a high prevalence of autism in children with congenital rubella syndrome (CRS), 200 times that of the general population at the time. Many researchers quote this fact to add proof to the current theory that maternal infection with immune system activation in pregnancy leads to autism in the offspring. This rubella and autism association is presented with the notion that rubella has been eliminated in today’s world. CRS cases are no longer typically seen; yet, autistic children often share findings of CRS including deafness, congenital heart defects, and to a lesser extent visual changes. Autistic children commonly have hyperactivity and spasticity, as do CRS children. Both autistic and CRS individuals may develop type 1 diabetes as young adults. Neuropathology of CRS infants may reveal cerebral vasculitis with narrowed lumens and cerebral necrosis. Neuroradiological findings of children with CRS show calcifications, periventricular leukomalacia, and dilated perivascular spaces. Neuroradiology of autism has also demonstrated hyperintensities, leukomalacia, and prominent perivascular spaces. PET studies of autistic individuals exhibit decreased perfusion to areas of the brain similarly affected by rubella. In both autism and CRS, certain changes in the brain have implicated the immune system. Several children with autism lack antibodies to rubella, as do children with CRS. These numerous similarities increase the probability of an association between rubella virus and autism. Rubella and autism cross many ethnicities in many countries. Contrary to current belief, rubella has not been eradicated and globally affects up to 5% of pregnant women. Susceptibility continues as vaccines are not given worldwide and are not fully protective. Rubella might still cause autism, even in vaccinated populations.

The promise of multi-omics and clinical data integration to identify and target personalized healthcare approaches in autism spectrum disorders

Complex diseases are caused by a combination of genetic and environmental factors, creating a difficult challenge for diagnosis and defining subtypes. This review article describes how distinct disease subtypes can be identified through integration and analysis of clinical and multi-omics data. A broad shift toward molecular subtyping of disease using genetic and omics data has yielded successful results in cancer and other complex diseases. To determine molecular subtypes, patients are first classified by applying clustering methods to different types of omics data, then these results are integrated with clinical data to characterize distinct disease subtypes. An example of this molecular-data-first approach is in research on Autism Spectrum Disorder (ASD), a spectrum of social communication disorders marked by tremendous etiological and phenotypic heterogeneity. In the case of ASD, omics data such as exome sequences and gene and protein expression data are combined with clinical data such as psychometric testing and imaging to enable subtype identification. Novel ASD subtypes have been proposed, such as CHD8, using this molecular subtyping approach. Broader use of molecular subtyping in complex disease research is impeded by data heterogeneity, diversity of standards, and ineffective analysis tools. The future of molecular subtyping for ASD and other complex diseases calls for an integrated resource to identify disease mechanisms, classify new patients, and inform effective treatment options. This in turn will empower and accelerate precision medicine and personalized healthcare.

Visual and Vestibular Induced Eye Movements in Verbal Children and Adults with Autism

This study assessed the functionality of vestibular, pursuit, and saccade circuitry in autism across a wide age range. Subjects were 79 individuals with autism (AUT) and 62 controls (CON) aged 5 to 52 years with IQ scores > 70. For vestibular testing, earth-vertical axis rotation was performed in darkness and in a lighted visual surround with a fixation target. Ocular motor testing included assessment of horizontal saccades and horizontal smooth pursuit. No between-group differences were found in vestibular reflexes or in mean saccade velocity or accuracy. Saccade latency was increased in the AUT group with significant age-related effects in the 8-18 year old subgroups. There was a trend toward decreased pursuit gain without age effects. Normal vestibular-induced eye movements and normal saccade accuracy and velocity provide the most substantial evidence to date of the functional integrity of brainstem and cerebellar pathways in autism, suggesting that the histopathological abnormalities described in these structures may not be associated with intrinsic dysfunction but rather reflect developmental alterations related to forebrain cortical systems formation. Increased saccade latency with age effects adds to the extensive existing evidence of altered function and maturation of cortical systems in autism.

Autistic fluid intelligence: Increased reliance on visual functional connectivity with diminished modulation of coupling by task difficulty

Different test types lead to different intelligence estimates in autism, as illustrated by the fact that autistic individuals obtain higher scores on the Raven's Progressive Matrices (RSPM) test than they do on the Wechsler IQ, in contrast to relatively similar performance on both tests in non-autistic individuals. However, the cerebral processes underlying these differences are not well understood. This study investigated whether activity in the fluid “reasoning” network, which includes frontal, parietal, temporal and occipital regions, is differently modulated by task complexity in autistic and non-autistic individuals during the RSPM. In this purpose, we used fMRI to study autistic and non-autistic participants solving the 60 RSPM problems focussing on regions and networks involved in reasoning complexity. As complexity increased, activity in the left superior occipital gyrus and the left middle occipital gyrus increased for autistic participants, whereas non-autistic participants showed increased activity in the left middle frontal gyrus and bilateral precuneus. Using psychophysiological interaction analyses (PPI), we then verified in which regions did functional connectivity increase as a function of reasoning complexity. PPI analyses revealed greater connectivity in autistic, compared to non-autistic participants, between the left inferior occipital gyrus and areas in the left superior frontal gyrus, right superior parietal lobe, right middle occipital gyrus and right inferior temporal gyrus. We also observed generally less modulation of the reasoning network as complexity increased in autistic participants. These results suggest that autistic individuals, when confronted with increasing task complexity, rely mainly on visuospatial processes when solving more complex matrices. In addition to the now well-established enhanced activity observed in visual areas in a range of tasks, these results suggest that the enhanced reliance on visual perception has a central role in autistic cognition.

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Reasoning network is less modulated by problem complexity in autism.

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Autistic individuals rely more extensively on visuospatial processes to solve complex problems.

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Results support the central role of visual perception in autistic cognition.

Axon guidance proteins in neurological disorders

Many neurological disorders are characterised by structural changes in neuronal connections, ranging from presymptomatic synaptic changes to the loss or rewiring of entire axon bundles. The molecular mechanisms that underlie this perturbed connectivity are poorly understood, but recent studies suggest a role for axon guidance proteins. Axon guidance proteins guide growing axons during development and control structural plasticity of synaptic connections in adults. Changes in expression or function of these proteins might induce pathological changes in neural circuits that predispose to, or cause, neurological diseases. For some neurological disorders, such as midline crossing disorders, investigators have identified causative mutations in genes for axon guidance. However, for most other disorders, evidence is correlative and further studies are needed to confirm the pathological role of defects in proteins for axon guidance. Importantly, further insight into how dysregulation of axon guidance proteins causes disease will help the development of therapeutic strategies for neurological disorders.

Autism spectrum disorder and particulate matter air pollution before, during, and after pregnancy: a nested case-control analysis within the Nurses' Health Study II Cohort

BACKGROUND

Autism spectrum disorder (ASD) is a developmental disorder with increasing prevalence worldwide, yet has unclear etiology.

OBJECTIVE

We explored the association between maternal exposure to particulate matter (PM) air pollution and odds of ASD in her child.

METHODS

We conducted a nested case-control study of participants in the Nurses' Health Study II (NHS II), a prospective cohort of 116,430 U.S. female nurses recruited in 1989, followed by biennial mailed questionnaires. Subjects were NHS II participants' children born 1990-2002 with ASD (n = 245), and children without ASD (n = 1,522) randomly selected using frequency matching for birth years. Diagnosis of ASD was based on maternal report, which was validated against the Autism Diagnostic Interview-Revised in a subset. Monthly averages of PM with diameters ≤ 2.5 μm (PM2.5) and 2.5-10 μm (PM10-2.5) were predicted from a spatiotemporal model for the continental United States and linked to residential addresses.

RESULTS

PM2.5 exposure during pregnancy was associated with increased odds of ASD, with an adjusted odds ratio (OR) for ASD per interquartile range (IQR) higher PM2.5 (4.42 μg/m3) of 1.57 (95% CI: 1.22, 2.03) among women with the same address before and after pregnancy (160 cases, 986 controls). Associations with PM2.5 exposure 9 months before or after the pregnancy were weaker in independent models and null when all three time periods were included, whereas the association with the 9 months of pregnancy remained (OR = 1.63; 95% CI: 1.08, 2.47). The association between ASD and PM2.5 was stronger for exposure during the third trimester (OR = 1.42 per IQR increase in PM2.5; 95% CI: 1.09, 1.86) than during the first two trimesters (ORs = 1.06 and 1.00) when mutually adjusted. There was little association between PM10-2.5 and ASD.

CONCLUSIONS

Higher maternal exposure to PM2.5 during pregnancy, particularly the third trimester, was associated with greater odds of a child having ASD.

The relevance of human fetal subplate zone for developmental neuropathology of neuronal migration disorders and cortical dysplasia

The human fetal cerebral cortex develops through a series of partially overlapping histogenetic events which occur in transient cellular compartments, such as the subplate zone. The subplate serves as waiting compartment for cortical afferent fibers, the major site of early synaptogenesis and neuronal differentiation and the hub of the transient fetal cortical circuitry. Thus, the subplate has an important but hitherto neglected role in the human fetal cortical connectome. The subplate is also an important compartment for radial and tangential migration of future cortical neurons. We review the diversity of subplate neuronal phenotypes and their involvement in cortical circuitry and discuss the complexity of late neuronal migration through the subplate as well as its potential relevance for pathogenesis of migration disorders and cortical dysplasia. While migratory neurons may become misplaced within the subplate, they can easily survive by being involved in early subplate circuitry; this can enhance their subsequent survival even if they have immature or abnormal physiological activity and misrouted connections and thus survive into adulthood. Thus, better understanding of subplate developmental history and various subsets of its neurons may help to elucidate certain types of neuronal disorders, including those accompanied by epilepsy.

Molecular networks and the evolution of human cognitive specializations

Inroads into elucidating the origins of human cognitive specializations have taken many forms, including genetic, genomic, anatomical, and behavioral assays that typically compare humans to non-human primates. While the integration of all of these approaches is essential for ultimately understanding human cognition, here, we review the usefulness of coexpression network analysis for specifically addressing this question. An increasing number of studies have incorporated coexpression networks into brain expression studies comparing species, disease versus control tissue, brain regions, or developmental time periods. A clearer picture has emerged of the key genes driving brain evolution, as well as the developmental and regional contributions of gene expression patterns important for normal brain development and those misregulated in cognitive diseases.

Developmental dynamics of radial vulnerability in the cerebral compartments in preterm infants and neonates

The developmental vulnerability of different classes of axonal pathways in preterm white matter is not known. We propose that laminar compartments of the developing cerebral wall serve as spatial framework for axonal growth and evaluate potential of anatomical landmarks for understanding reorganization of the cerebral wall after perinatal lesions. The 3-T MRI (in vivo) and histological analysis were performed in a series of cases ranging from 22 postconceptional weeks to 3 years. For the follow-up scans, three groups of children (control, normotypic, and preterms with lesions) were examined at the term equivalent age and after the first year of life. MRI and histological abnormalities were analyzed in the following compartments: (a) periventricular, with periventricular fiber system; (b) intermediate, with periventricular crossroads, sagittal strata, and centrum semiovale; (c) superficial, composed of gyral white matter, subplate, and cortical plate. Vulnerability of thalamocortical pathways within the crossroads and sagittal strata seems to be characteristic for early preterms, while vulnerability of long association pathways in the centrum semiovale seems to be predominant feature of late preterms. The structural indicator of the lesion of the long association pathways is the loss of delineation between centrum semiovale and subplate remnant, which is possible substrate of the diffuse periventricular leukomalacia. The enhanced difference in MR signal intensity of centrum semiovale and subplate remnant, observed in damaged children after first year, we interpret as structural plasticity of intact short cortico-cortical fibers, which grow postnatally through U-zones and enter the cortex through the subplate remnant. Our findings indicate that radial distribution of MRI signal abnormalities in the cerebral compartments may be related to lesion of different classes of axonal pathways and have prognostic value for predicting the likely outcome of prenatal and perinatal lesions.

[High-functioning autism spectrum disorders in adulthood]

The prevalence of autism spectrum disorders in the general population is approximately 1 %. Some individuals with high-functioning autism graduate from regular schools without autism having been diagnosed and problems only occur when the demands for social competence increase. Then patients often present with secondary psychiatric symptoms, such as depression, anxiety or interpersonal problems. At this time, typical autistic features, such as social interaction deficits, restricted interests and stereotypic behavior can be camouflaged by high compensatory skills, particularly in highly intelligent patients. Therefore, missed or wrong diagnoses are frequent. Interviews, questionnaires and neuropsychological tests might be used to support the diagnosis. In cases where there is evidence for a secondary cause of autistic symptoms, somatic disorders should be excluded. Pharmacological treatment should be symptom-oriented. Individualized psychotherapeutic approaches are becoming increasingly more available; however, pragmatic solutions often need to be deployed.

Optimization of electron microscopy for human brains with long-term fixation and fixed-frozen sections

BACKGROUND

Abnormal connectivity across brain regions underlies many neurological disorders including multiple sclerosis, schizophrenia and autism, possibly due to atypical axonal organization within white matter. Attempts at investigating axonal organization on post-mortem human brains have been hindered by the availability of high-quality, morphologically preserved tissue, particularly for neurodevelopmental disorders such as autism. Brains are generally stored in a fixative for long periods of time (often greater than 10 years) and in many cases, already frozen and sectioned on a microtome for histology and immunohistochemistry. Here we present a method to assess the quality and quantity of axons from long-term fixed and frozen-sectioned human brain samples to demonstrate their use for electron microscopy (EM) measures of axonal ultrastructure.

RESULTS

Six samples were collected from white matter below the superior temporal cortex of three typically developing human brains and prepared for EM analyses. Five samples were stored in fixative for over 10 years, two of which were also flash frozen and sectioned on a freezing microtome, and one additional case was fixed for 3 years and sectioned on a freezing microtome. In all six samples, ultrastructural qualitative and quantitative analyses demonstrate that myelinated axons can be identified and counted on the EM images. Although axon density differed between brains, axonal ultrastructure and density was well preserved and did not differ within cases for fixed and frozen tissue. There was no significant difference between cases in axon myelin sheath thickness (g-ratio) or axon diameter; approximately 70% of axons were in the small (0.25 μm) to medium (0.75 μm) range. Axon diameter and g-ratio were positively correlated, indicating that larger axons may have thinner myelin sheaths.

CONCLUSION

The current study demonstrates that long term formalin fixed and frozen-sectioned human brain tissue can be used for ultrastructural analyses. Axon integrity is well preserved and can be quantified using the methods presented here. The ability to carry out EM on frozen sections allows for investigation of axonal organization in conjunction with other cellular and histological methods, such as immunohistochemistry and stereology, within the same brain and even within the same frozen cut section.

DAWN: a framework to identify autism genes and subnetworks using gene expression and genetics

BACKGROUND

De novo loss-of-function (dnLoF) mutations are found twofold more often in autism spectrum disorder (ASD) probands than their unaffected siblings. Multiple independent dnLoF mutations in the same gene implicate the gene in risk and hence provide a systematic, albeit arduous, path forward for ASD genetics. It is likely that using additional non-genetic data will enhance the ability to identify ASD genes.

METHODS

To accelerate the search for ASD genes, we developed a novel algorithm, DAWN, to model two kinds of data: rare variations from exome sequencing and gene co-expression in the mid-fetal prefrontal and motor-somatosensory neocortex, a critical nexus for risk. The algorithm casts the ensemble data as a hidden Markov random field in which the graph structure is determined by gene co-expression and it combines these interrelationships with node-specific observations, namely gene identity, expression, genetic data and the estimated effect on risk.

RESULTS

Using currently available genetic data and a specific developmental time period for gene co-expression, DAWN identified 127 genes that plausibly affect risk, and a set of likely ASD subnetworks. Validation experiments making use of published targeted resequencing results demonstrate its efficacy in reliably predicting ASD genes. DAWN also successfully predicts known ASD genes, not included in the genetic data used to create the model.

CONCLUSIONS

Validation studies demonstrate that DAWN is effective in predicting ASD genes and subnetworks by leveraging genetic and gene expression data. The findings reported here implicate neurite extension and neuronal arborization as risks for ASD. Using DAWN on emerging ASD sequence data and gene expression data from other brain regions and tissues would likely identify novel ASD genes. DAWN can also be used for other complex disorders to identify genes and subnetworks in those disorders.