Balance and Vestibular Deficits in Pediatric Patients with Autism Spectrum Disorder: An Underappreciated Clinical Aspect

Evidence of vestibular dysfunction in children with enlarged vestibular aqueduct

Neurodevelopmental disorders (NDDs) are a complex grouping of conditions arising in childhood relating to altered development and function of the brain. The primary conditions classified as NDDs include autism spectrum disorder (ASD), intellectual disability, attention deficit hyperactivity disorder, as well as motor, communication, and specific learning disorders. Many NDDs are known to have significant genetic risk, but the particular genes and molecular pathways controlling this genetic risk are still poorly understood. In addition to the genetic etiology of NDDs themselves, understanding the role of genetics in commonly associated comorbidities, such as sleep dysfunction or epilepsy in ASD, and how these insights might be leveraged to develop new therapeutics, remains a central goal of NDD genetic research. In ASD in particular, mutations in more than 100 genes have been significantly linked to increased risk for ASD. However, projections based on the frequency of mutations in these known risk genes has suggested that over 1000 genes may significantly increase risk for ASD when mutated. In response to this prediction, several machine learning approaches have been developed to use genome-wide data sources to predict which genes are the best candidates for ASD risk gene discovery. However, with different sources of data and training strategies used for each of these scores, there is not a clear consensus in the community on the most important predictors of genetic risk. My work develops a new ASD risk gene score that combines the benefits of all prior scores through a machine learning approach called ”ensemble learning”, unifying the previous scores while providing additional genome-wide data sources for model training. By comparing the previous scores with my work, I demonstrate the effectiveness of ensemble learning in this setting, and provide an ASD risk gene score that is enriched across a variety of ASD genetic data domains, such as common variant risk and gene expression data. While ASD as a whole has many known genetic associations, differences in medical issues experienced by those with ASD are highly variable, and the genetic factors underlying these comorbidities remain unclear. For instance, more than 70% of individuals with ASD have issues with sleep, but it is unknown whether genetic changes explain this difference seen between individuals with of ASD. Simply put, we know that genetics plays a large role in ASD, but we do not know the specifics of how genes map to subtypes of ASD. My work bridges this gap by studying the genetics of sleep dysfunction within individuals with ASD. To my knowledge, I am the first to be able to demonstrate and report that sleep dysfunction in ASD has a significant genetic component. Further, I find that genetic risk for ADHD, BMI, and several other conditions heightens an autistic individual’s risk for having issues with sleep. This work also uncovers associations between the type of sleep issue an individual has and the drugs that may be most effective for restoring normal sleep. Another major medical issue faced by individuals with ASD is epilepsy, with over 20% of individuals diagnosed with ASD having or going on to develop epilepsy later in life. Similar to sleep issues in ASD, treatment options in epilepsy are often effective but fall short in approximately 30% of cases. Finding treatments for these individuals who fail to find relief from the standard of care options is of critical importance. My work uses a bioinformatic technique called drug repositioning to computationally prioritize drugs that may be capable of reversing the transcriptional state induced by epilepsy. This approach yielded 184 potential therapeutic compounds, of which 4 were selected and tested in a zebrafish model of epilepsy. Three of the four compounds showed significant seizure suppression activity, including one with no previous literature surrounding its use in epilepsy (pyrantel tartrate). While a diverse set of work, the common thread is leveraging computational genetic techniques to better understand the causes, symptoms, and treatments of neurodevelopmental and associated disorders. By using ensemble learning, this work establishes a unified autism risk gene score that effectively summarizes a gene’s level of association with autism. Through studying sleep issues in ASD, I find a significant role for common variant risk and establish several genetic associations for poor sleep in ASD, such as ADHD and BMI genetic risk factors. Lastly, by using gene expression to model an effective therapeutic for epilepsy, this work reports on the first possible use of pyrantel tartrate in the treatment of epilepsy. Taken together, these findings demonstrate the power of leveraging big genetic datasets and innovative techniques in order to understand complex disease.

The role of immune dysfunction in the pathophysiology of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder affecting 1 in 36 children and is associated with physiological abnormalities, most notably mitochondrial dysfunction, at least in a subset of individuals. This systematic review and meta-analysis discovered 204 relevant articles which evaluated biomarkers of mitochondrial dysfunction in ASD individuals. Significant elevations (all p < 0.01) in the prevalence of lactate (17%), pyruvate (41%), alanine (15%) and creatine kinase (9%) were found in ASD. Individuals with ASD had significant differences (all p < 0.01) with moderate to large effect sizes (Cohen's d’ ≥ 0.6) compared to controls in mean pyruvate, lactate-to-pyruvate ratio, ATP, and creatine kinase. Some studies found abnormal TCA cycle metabolites associated with ASD. Thirteen controlled studies reported mitochondrial DNA (mtDNA) deletions or variations in the ASD group in blood, peripheral blood mononuclear cells, lymphocytes, leucocytes, granulocytes, and brain. Meta-analyses discovered significant differences (p < 0.01) in copy number of mtDNA overall and in ND1, ND4 and CytB genes. Four studies linked specific mtDNA haplogroups to ASD. A series of studies found a subgroup of ASD with elevated mitochondrial respiration which was associated with increased sensitivity of the mitochondria to physiological stressors and neurodevelopmental regression. Lactate, pyruvate, lactate-to-pyruvate ratio, carnitine, and acyl-carnitines were associated with clinical features such as delays in language, social interaction, cognition, motor skills, and with repetitive behaviors and gastrointestinal symptoms, although not all studies found an association. Lactate, carnitine, acyl-carnitines, ATP, CoQ10, as well as mtDNA variants, heteroplasmy, haplogroups and copy number were associated with ASD severity. Variability was found across biomarker studies primarily due to differences in collection and processing techniques as well as the intrinsic heterogeneity of the ASD population. Several studies reported alterations in mitochondrial metabolism in mothers of children with ASD and in neonates who develop ASD. Treatments targeting mitochondria, particularly carnitine and ubiquinol, appear beneficial in ASD. The link between mitochondrial dysfunction in ASD and common physiological abnormalities in individuals with ASD including gastrointestinal disorders, oxidative stress, and immune dysfunction is outlined. Several subtypes of mitochondrial dysfunction in ASD are discussed, including one related to neurodevelopmental regression, another related to alterations in microbiome metabolites, and another related to elevations in acyl-carnitines. Mechanisms linking abnormal mitochondrial function with alterations in prenatal brain development and postnatal brain function are outlined. Given the multisystem complexity of some individuals with ASD, this review presents evidence for the mitochondria being central to ASD by contributing to abnormalities in brain development, cognition, and comorbidities such as immune and gastrointestinal dysfunction as well as neurodevelopmental regression. A diagnostic approach to identify mitochondrial dysfunction in ASD is outlined. From this evidence, it is clear that many individuals with ASD have alterations in mitochondrial function which may need to be addressed in order to achieve optimal clinical outcomes. The fact that alterations in mitochondrial metabolism may be found during pregnancy and early in the life of individuals who eventually develop ASD provides promise for early life predictive biomarkers of ASD. Further studies may improve the understanding of the role of the mitochondria in ASD by better defining subgroups and understanding the molecular mechanisms driving some of the unique changes found in mitochondrial function in those with ASD.

Vertigo is a complex symptom which imposes diagnostic and treatment challenges. Laboratory evaluation of vertigo includes video-nystagmography (VNG) and computerized dynamic posturography (CDP) for the evaluation of different aspects of this complaint. There are vague indications for each test and potential disagreements between them. The aim of this study is to examine the association between the test results of the VNG and sensory organization test (SOT) of CDP in patients referred for both vestibular tests. Retrospective data regarding 56 patients age 17-82years were collected. Patients suffered vestibular complaints and were referred for VNG and CDP evaluation on the same day. The level of agreement between VNG (including caloric test) and the vestibular input of the SOT for each patient was calculated. Among the study group, 10 showed abnormal caloric test results, of which 3 (5.4%) had normal vestibular input in the SOT, and 7 (12.5%) had impaired input (p = 0.724). Spontaneous nystagmus was recorded in 13 patients by VNG, of which 2(3.6%) had normal vestibular input and 11(19.6%) had impaired vestibular input (p = 0.056). This study shows no statistically significant association between the VNG test and SOT test results. Our results emphasize the difference between the tested aspects in each laboratory test, and the need to define specific indications for each of them. There is a marginally significant association between impaired vestibular input and spontaneous nystagmus, demonstrating the non-localizing nature of this sign.

Background:Dizziness is the second most common symptom in people who sustain a concussion and there are few reports on vestibular laboratory findings in the concussed pediatric population. Studies to date have shown conflicting findings regarding incidence of peripheral vestibular disorders. Hypothesis/Purpose: The purpose of this study is to report vestibular laboratory and clinical examination findings in concussed youth referred to a multidisciplinary vestibular clinic.Methods:A retrospective chart review was performed for all patients (n=474) seen from August 2017 to March 2020 for a single comprehensive examination in a multidisciplinary pediatric vestibular specialty clinic. Data was extracted from the charts of patients (n=64) with a history of concussion referred because of chronic dizziness and/or imbalance. Each patient was examined by a neurotologist, physical therapist, and audiologist with specialized training in vestibular disorders. Vestibular laboratory testing performed by audiologists included video nystagmography (VNG) evaluation of oculomotor function and BPPV, rotational chair, video head impulse test (vHIT), vestibular evoked myogenic potentials (VEMPs), post-headshake nystagmus, and caloric irrigation. Physical therapy clinical examination included dynamic visual acuity testing (DVA), vestibular/oculomotor screening (VOMS), and sensory organization test (SOT). Not all tests were performed on every patient secondary to factors such as insurance coverage, patient tolerance, and young age.Results:1 or more components of VOMS was abnormal in 30 of 53 patients examined. DVA was completed on 40 patients, 23 of which were reported as abnormal. SOT was completed on 46 patients, 18 of which demonstrated below normal composite equilibrium scores. Laboratory findings were as follows: VEMPs (n=50) were normal in all but 1 patient, vHIT (n=59), caloric irrigation (n=26), post-headshake nystagmus (n=49), and positional testing (n=55) were normal on all patients tested. Rotational chair (n=60) was performed at 4 different frequencies and revealed low gain in 3 patients.Conclusion:Vestibular laboratory examination was normal in nearly all subjects tested. These results suggest that in concussed youth with chronic dizziness and/or imbalance, laboratory vestibular test outcomes indicative of peripheral dysfunction are rare, which contradicts previous research in this population. In contrast, clinical vestibular assessment was abnormal in more than 50% of subjects examined which suggests that clinicians should use caution interpreting clinical examination findings for diagnosing peripheral vestibular dysfunction. Abnormal clinical examination findings may be indicative of central vestibular conditions such as space and motion intolerance and PPPD in chronically dizzy pediatric patients after concussion.Tables/Figures:

Perioperative vestibular assessment and testing

Autism spectrum disorder (ASD) affects ~ 2% of children in the United States. The etiology of ASD likely involves environmental factors triggering physiological abnormalities in genetically sensitive individuals. One of these major physiological abnormalities is mitochondrial dysfunction, which may affect a significant subset of children with ASD. Here we systematically review the literature on human studies of mitochondrial dysfunction related to ASD. Clinical aspects of mitochondrial dysfunction in ASD include unusual neurodevelopmental regression, especially if triggered by an inflammatory event, gastrointestinal symptoms, seizures, motor delays, fatigue and lethargy. Traditional biomarkers of mitochondrial disease are widely reported to be abnormal in ASD, but appear non-specific. Newer biomarkers include buccal cell enzymology, biomarkers of fatty acid metabolism, non-mitochondrial enzyme function, apoptosis markers and mitochondrial antibodies. Many genetic abnormalities are associated with mitochondrial dysfunction in ASD, including chromosomal abnormalities, mitochondrial DNA mutations and large-scale deletions, and mutations in both mitochondrial and non-mitochondrial nuclear genes. Mitochondrial dysfunction has been described in immune and buccal cells, fibroblasts, muscle and gastrointestinal tissue and the brains of individuals with ASD. Several environmental factors, including toxicants, microbiome metabolites and an oxidized microenvironment are shown to modulate mitochondrial function in ASD tissues. Investigations of treatments for mitochondrial dysfunction in ASD are promising but preliminary. The etiology of mitochondrial dysfunction and how to define it in ASD is currently unclear. However, preliminary evidence suggests that the mitochondria may be a fruitful target for treatment and prevention of ASD. Further research is needed to better understand the role of mitochondrial dysfunction in the pathophysiology of ASD.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by repetitive behaviors, poor social skills, and difficulties with communication. Beyond these core signs and symptoms, the majority of subjects with ASD have some degree of auditory and vestibular dysfunction. Dysfunction in these sensory modalities is significant as normal cognitive development depends on an accurate representation of our environment. The hearing difficulties in ASD range from deafness to hypersensitivity and subjects with ASD have abnormal sound-evoked brainstem reflexes and brainstem auditory evoked potentials. Vestibular dysfunction in ASD includes postural instability, gait dysfunction, and impaired gaze. Untreated vestibular dysfunction in children can lead to delayed milestones such as sitting and walking and poor motor coordination later in life. Histopathological studies have revealed that subjects with ASD have significantly fewer neurons in the auditory hindbrain and surviving neurons are smaller and dysmorphic. These findings are consistent with auditory dysfunction. Further, the cerebellum was one of the first brain structures implicated in ASD and studies have revealed loss of Purkinje cells and the presence of ectopic neurons. Together, these studies suggest that normal auditory and vestibular function play major roles in the development of language and social abilities, and dysfunction in these systems may contribute to the core symptoms of ASD. Further, auditory and vestibular dysfunction in children may be overlooked or attributed to other neurodevelopmental disorders. Herein we review the literature on auditory and vestibular dysfunction in ASD. Based on these results we developed a brainstem model of central auditory and vestibular dysfunction in ASD and propose that simple, non-invasive but quantitative testing of hearing and vestibular function be added to newborn screening protocols.

A comprehensive literature search was performed to collate evidence of mitochondrial dysfunction in autism spectrum disorders (ASDs) with two primary objectives. First, features of mitochondrial dysfunction in the general population of children with ASD were identified. Second, characteristics of mitochondrial dysfunction in children with ASD and concomitant mitochondrial disease (MD) were compared with published literature of two general populations: ASD children without MD, and non-ASD children with MD. The prevalence of MD in the general population of ASD was 5.0% (95% confidence interval 3.2, 6.9%), much higher than found in the general population (∼0.01%). The prevalence of abnormal biomarker values of mitochondrial dysfunction was high in ASD, much higher than the prevalence of MD. Variances and mean values of many mitochondrial biomarkers (lactate, pyruvate, carnitine and ubiquinone) were significantly different between ASD and controls. Some markers correlated with ASD severity. Neuroimaging, in vitro and post-mortem brain studies were consistent with an elevated prevalence of mitochondrial dysfunction in ASD. Taken together, these findings suggest children with ASD have a spectrum of mitochondrial dysfunction of differing severity. Eighteen publications representing a total of 112 children with ASD and MD (ASD/MD) were identified. The prevalence of developmental regression (52%), seizures (41%), motor delay (51%), gastrointestinal abnormalities (74%), female gender (39%), and elevated lactate (78%) and pyruvate (45%) was significantly higher in ASD/MD compared with the general ASD population. The prevalence of many of these abnormalities was similar to the general population of children with MD, suggesting that ASD/MD represents a distinct subgroup of children with MD. Most ASD/MD cases (79%) were not associated with genetic abnormalities, raising the possibility of secondary mitochondrial dysfunction. Treatment studies for ASD/MD were limited, although improvements were noted in some studies with carnitine, co-enzyme Q10 and B-vitamins. Many studies suffered from limitations, including small sample sizes, referral or publication biases, and variability in protocols for selecting children for MD workup, collecting mitochondrial biomarkers and defining MD. Overall, this evidence supports the notion that mitochondrial dysfunction is associated with ASD. Additional studies are needed to further define the role of mitochondrial dysfunction in ASD.

Autism spectrum disorder (ASD) is a complex disorder that is underpinned by numerous dysregulated biological pathways, including pathways that affect mitochondrial function. Epigenetic mechanisms contribute to this dysregulation and DNA methylation is an important factor in the etiology of ASD. We measured DNA methylation of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α), as well as five genes involved in regulating mitochondrial homeostasis to examine mitochondrial dysfunction in an ASD cohort of South African children. Using targeted Next Generation bisulfite sequencing, we found differential methylation (p < 0.05) at six key genes converging on mitochondrial biogenesis, fission and fusion in ASD, namely PGC-1α, STOML2, MFN2, FIS1, OPA1, and GABPA. PGC-1α, the transcriptional regulator of biogenesis, was significantly hypermethylated at eight CpG sites in the gene promoter, one of which contained a putative binding site for CAMP response binding element 1 (CREB1) (p = 1 × 10–6). Mitochondrial DNA (mtDNA) copy number, a marker of mitochondrial function, was elevated (p = 0.002) in ASD compared to controls and correlated significantly with DNA methylation at the PGC-1α promoter and there was a positive correlation between methylation at PGC-1α CpG#1 and mtDNA copy number (Spearman’s r = 0.2, n = 49, p = 0.04) in ASD. Furthermore, DNA methylation at PGC-1α CpG#1 and mtDNA copy number correlated significantly (p < 0.05) with levels of urinary organic acids associated with mitochondrial dysfunction, oxidative stress, and neuroendocrinology. Our data show differential methylation in ASD at six key genes converging on PGC-1α-dependent regulation of mitochondrial biogenesis and function. We demonstrate that methylation at the PGC-1α promoter is associated with elevated mtDNA copy number and metabolomic evidence of mitochondrial dysfunction in ASD. This highlights an unexplored role for DNA methylation in regulating specific pathways involved in mitochondrial biogenesis, fission and fusion contributing to mitochondrial dysfunction in ASD.

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder characterized by communication and social behavior deficits. The presence of restricted and repetitive behaviors often accompanies these deficits, and these characteristics can range from mild to severe. The past several decades have seen a significant rise in the prevalence of ASD. The etiology of ASD remains unknown; however, genetic and environmental risk factors play a role. Multiple hypotheses converge to suggest that neuroinflammation, or at least the interaction between immune and neural systems, may be involved in the etiology of some ASD cases or groups. Repeated evidence of innate immune dysfunction has been seen in ASD, often associated with worsening behaviors. This evidence includes data from circulating myeloid cells and brain resident macrophages/microglia in both human and animal models. This comprehensive review presents recent findings of innate immune dysfunction in ASD, including aberrant innate cellular function, evidence of neuroinflammation, and microglia activation. Appeared originally in Brain Behav Immun 2023; 108:245-254.

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder characterized by communication and social behavior deficits. The presence of restricted and repetitive behaviors often accompanies these deficits, and these characteristics can range from mild to severe. The past several decades have seen a significant rise in the prevalence of ASD. The etiology of ASD remains unknown; however, genetic and environmental risk factors play a role. Multiple hypotheses converge to suggest that neuroinflammation, or at least the interaction between immune and neural systems, may be involved in the etiology of some ASD cases or groups. Repeated evidence of innate immune dysfunction has been seen in ASD, often associated with worsening behaviors. This evidence includes data from circulating myeloid cells and brain resident macrophages/microglia in both human and animal models. This comprehensive review presents recent findings of innate immune dysfunction in ASD, including aberrant innate cellular function, evidence of neuroinflammation, and microglia activation.

As the world moves towards the Fourth Industrial Revolution, there is a need for formulations of neurophysiological biomarkers that ensure the accuracy of the diagnosis of visual perception dysfunction in individuals with Autism Spectrum Disorder (ASD). Biomarkers of visual perception dysfunction in ASD using EEG complements behavioral methods of diagnosis and allows for a more direct assessment of the dysfunction, identifying rapid, implicit neural processes that are not revealed through behavioral measures alone. This paper aims to review the neural biomarkers of the five domains of visual perception dysfunction (visual discrimination (VD), visual spatial relations (VSR), visual form constancy (VFC), visual memory (VM) and visual closure (VC)) in individuals with ASD. This paper shall help researchers gain new insight into the current trends and progress in EEG methods in ASD and discover gaps in the subject literature. A systematic literature search on PubMed was conducted to report findings of EEG studies that:1) assessed the severity levels in patients with ASD and 2) investigated the neural biomarkers of visual perception dysfunction in ASD. Spectral analysis, functional connectivity analysis and event-related potential (ERP) are useful in modern medicine to identify the biomarkers that distinguish the levels of the severity of visual perception dysfunction in ASD.

Background: Postural control deficits have been documented in children with autism spectrum disorder (ASD), yet vestibular system contributions to postural control have not been widely considered. The purpose of this study is to explore the relationship between functional balance, postural sway, and vestibular function in children with ASD. Methods: Ten children with a confirmed diagnosis of ASD according to DSM-V guidelines along with ten children with no known neurodevelopmental or motor delays participated in the study. Bruininks-Oseretsky Test of Motor Proficiency and the Paediatric Balance Scale measured functional balance ability, and postural sway was measured using static posturography with modified sensory inputs. Peripheral vestibular function was measured using cervical vestibular evoked myogenic potentials and video head impulse testing. Correlations between measures were performed. Results: When visual cues were removed, children with ASD demonstrated larger path velocities indicative of reduced postural control, and different patterns of postural sway. Functional balance was correlated with path velocities for conditions where sensory information was modified. No differences in peripheral vestibular function were noted between groups, and functional balance was not correlated with vestibular function. Conclusions: Findings suggest that while peripheral vestibular function is similar between groups, postural control differences in children with ASD remain, particularly for conditions where sensory information is modified. Furthermore, demonstrated patterns of postural sway suggest sensory system integration is less developed in children with ASD. These findings highlight the importance of utilising a range of clinical tools to quantify balance ability and consideration of postural control measures to inform intervention.