Longitudinal changes in diffusion properties in white matter pathways of children with tuberous sclerosis complex

Aspects of autism spectrum disorder and correlation with neuroimaging findings in tuberous sclerosis complex

BACKGROUND

Tuberous sclerosis complex (TSC) patients may have different specific neuropsychological deficits related to the location of the tubers. Autism spectrum disorders (ASD) are common in TSC patients but the relationship between these diagnoses has not been formally explored. In this study we sought to examine brain Magnetic Resonance Imaging (MRI) findings in TSC patients with ASD.

METHODS

We evaluated 34 TSC patients on the basis of DSM-V diagnostic criteria for ASD, Wechsler Intelligence Scale for Children (WISC-R), psychiatrist's examination and also structured parent interviews. The number and localization of the tubers, postcontrast signal characteristics of the tubers, SWI findings, DWI findings on brain MRI were recorded. Demographic features, epilepsy histories, number of antiseizure medications, cognitive status were eveluated also. Patients were divided into two groups: ASD group, which represented group 1 and group 2 consisting of patients without any ASD symptoms.

RESULTS

In our study, the mean number of tuber count was 21.8 in patients with ASD patients (Group 1, n = 13) and 12.4 in other TSC patients without ASD (Group 2, n = 21). Rate of tubers in prefrontal cortex/whole tubers (0.51) in patients with ASD was determined to be higher in group 1 (p = 0.003). Also a significant difference was detected between generalize epileptiform activities on EEG and the rate of DRE (p = 0.002; p = 0.001) between groups. Cognitive disturbances and infantile spasm history were similar between groups. TSC2 mutations have been identified in 29 (86%) patients.

CONCLUSION

The mean of total tuber count and the rate of the location in the prefrontal cortex were determined to be higher in TSC patients with ASD. Specific areas on brain MRI may help understanding the development of ASD in TSC patients.

To Stick or Not to Stick: The Multiple Roles of Cell Adhesion Molecules in Neural Circuit Assembly

Precise wiring of neural circuits is essential for brain connectivity and function. During development, axons respond to diverse cues present in the extracellular matrix or at the surface of other cells to navigate to specific targets, where they establish precise connections with post-synaptic partners. Cell adhesion molecules (CAMs) represent a large group of structurally diverse proteins well known to mediate adhesion for neural circuit assembly. Through their adhesive properties, CAMs act as major regulators of axon navigation, fasciculation, and synapse formation. While the adhesive functions of CAMs have been known for decades, more recent studies have unraveled essential, non-adhesive functions as well. CAMs notably act as guidance cues and modulate guidance signaling pathways for axon pathfinding, initiate contact-mediated repulsion for spatial organization of axonal arbors, and refine neuronal projections during circuit maturation. In this review, we summarize the classical adhesive functions of CAMs in axonal development and further discuss the increasing number of other non-adhesive functions CAMs play in neural circuit assembly.

Abnormal White Matter Microstructure in the Limbic System Is Associated With Tuberous Sclerosis Complex-Associated Neuropsychiatric Disorders

Objective

Tuberous sclerosis complex (TSC) is a genetic disease that arises from TSC1 or TSC2 abnormalities and induces the overactivation of the mammalian/mechanistic target of rapamycin pathways. The neurological symptoms of TSC include epilepsy and tuberous sclerosis complex-associated neuropsychiatric disorders (TAND). Although TAND affects TSC patients' quality of life, the specific region in the brain associated with TAND remains unknown. We examined the association between white matter microstructural abnormalities and TAND, using diffusion tensor imaging (DTI).

Methods

A total of 19 subjects with TSC and 24 age-matched control subjects were enrolled. Tract-based spatial statistics (TBSS) were performed to assess group differences in fractional anisotropy (FA) between the TSC and control groups. Atlas-based association analysis was performed to reveal TAND-related white matter in subjects with TSC. Multiple linear regression was performed to evaluate the association between TAND and the DTI parameters; FA and mean diffusivity in seven target regions and projection fibers.

Results

The TBSS showed significantly reduced FA in the right hemisphere and particularly in the inferior frontal occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), superior longitudinal fasciculus (SLF), uncinate fasciculus (UF), and genu of corpus callosum (CC) in the TSC group relative to the control group. In the association analysis, intellectual disability was widely associated with all target regions. In contrast, behavioral problems and autistic features were associated with the limbic system white matter and anterior limb of the internal capsule (ALIC) and CC.

Conclusion

The disruption of white matter integrity may induce underconnectivity between cortical and subcortical regions. These findings suggest that TANDs are not the result of an abnormality in a specific brain region, but rather caused by connectivity dysfunction as a network disorder. This study indicates that abnormal white matter connectivity including the limbic system is relevant to TAND. The analysis of brain and behavior relationship is a feasible approach to reveal TAND related white matter and neural networks. TAND should be carefully assessed and treated at an early stage.

Impaired myelin production due to an intrinsic failure of oligodendrocytes in mTORpathies

AIMS

We aim to evaluate if the myelin pathology observed in epilepsy-associated focal cortical dysplasia type 2B (FCD2B) and-histologically indistinguishable-cortical tubers of tuberous sclerosis complex (TSC) is primarily related to the underlying malformation or constitutes a secondary phenomenon due to the toxic microenvironment created by epileptic seizures. We also aim to investigate the possible beneficial effect of the mTOR pathway regulator everolimus on white matter pathology.

METHODS

Primary mixed glial cell cultures derived from epilepsy surgery specimens of one TSC and seven FCD2B patients were grown on polycaprolactone fibre matrices and analysed using immunofluorescence and electron microscopy. Unaffected white matter from three age-matched epilepsy patients with mild malformations of cortical development (mMCD) and one with FCD3D served as controls. Additionally, TSC2 knock-out was performed using an oligodendroglial cell line. Myelination capacities of nanofibre grown cells in an inflammatory environment after mTOR-inhibitor treatment with everolimus were further investigated.

RESULTS

Reduced oligodendroglial turnover, directly related to a lower myelin content was found in the patients' primary cells. In our culture model of myelination dynamics, primary cells grown under 'inflammatory condition' showed decreased myelination, that was repaired by treatment with everolimus.

CONCLUSIONS

Results obtained in patient-derived primary oligodendroglial and TSC2 knock-out cells suggest that maturation of oligodendroglia and production of a proper myelin sheath seem to be impaired as a result of mTOR pathway disturbance. Hence, oligodendroglial pathology may reflect a more direct effect of the abnormal genetic programme rather than to be an inactive bystander of chronic epilepsy.

Factors associated with autism spectrum disorder in children with tuberous sclerosis complex: a systematic review and meta-analysis

AIM

To investigate associations between clinical factors and the development of autism spectrum disorder (ASD) in children with tuberous sclerosis complex (TSC), specifically seizures, electroencephalogram abnormalities, tubers and other neurostructural abnormalities, and genetic factors.

METHOD

MEDLINE, Embase, PubMed, the Cochrane Library, and Web of Science were searched until January 2019. Studies that considered the predefined factors for development of ASD in children with TSC were included, following PRISMA-P guidelines. Two authors independently reviewed titles, abstracts, and full texts, extracted data, and assessed risk of bias.

RESULTS

Forty-two studies with 3542 children with TSC were included. ASD was associated with a history of seizures (odds ratio [OR] 3.79, 95% confidence interval [CI] 1.77-8.14), infantile spasms compared with other seizure types (OR 3.04, 95% CI 2.17-4.27), onset of any seizure type during infancy (OR 2.65, 95% CI 1.08-6.54), and male sex (OR 1.62, 95% CI 1.23-2.14). There was no association with tuber number, tuber location, or genotype.

INTERPRETATION

While a causal link between seizures and ASD in children with TSC cannot be inferred, a strong association between seizures and ASD in children with TSC, particularly with seizure onset during infancy and specifically infantile spasms, is present. Children with TSC and infant-onset seizures should be monitored for emerging features of ASD. What this paper adds Seizures and autism spectrum disorder (ASD) strongly associate in children with tuberous sclerosis complex (TSC). Infant-onset seizures and infantile spasms are particularly strongly associated with ASD in TSC.

RHOA signaling defects result in impaired axon guidance in iPSC-derived neurons from patients with tuberous sclerosis complex

Patients with Tuberous Sclerosis Complex (TSC) show aberrant wiring of neuronal connections formed during development which may contribute to symptoms of TSC, such as intellectual disabilities, autism, and epilepsy. Yet models examining the molecular basis for axonal guidance defects in developing human neurons have not been developed. Here, we generate human induced pluripotent stem cell (hiPSC) lines from a patient with TSC and genetically engineer counterparts and isogenic controls. By differentiating hiPSCs, we show that control neurons respond to canonical guidance cues as predicted. Conversely, neurons with heterozygous loss of TSC2 exhibit reduced responses to several repulsive cues and defective axon guidance. While TSC2 is a known key negative regulator of MTOR-dependent protein synthesis, we find that TSC2 signaled through MTOR-independent RHOA in growth cones. Our results suggest that neural network connectivity defects in patients with TSC may result from defects in RHOA-mediated regulation of cytoskeletal dynamics during neuronal development.

Patients with Tuberous Sclerosis Complex (TSC) show aberrant wiring of neuronal connections. Here, the authors generate iPSC-derived neurons from patients with TSC. TSC2 +/− neurons show impaired mTOR-independent RhoA signaling-mediated axon guidance.

Neuroimaging in tuberous sclerosis complex

INTRODUCTION

Tuberous sclerosis complex (TSC) is a rare autosomal dominant disorder affecting multiple systems, due to inactivating mutations of TSC1 or TSC2 mTOR pathway genes. Neurological manifestations are observed in about 95% cases, representing the most frequent cause of morbidity and one of the most common causes of mortality.

BACKGROUND

Neuroimaging is crucial for early diagnosis, monitoring, and management of these patients. While computed tomography is generally used as first-line investigation at emergency department, magnetic resonance imaging is the reference method to define central nervous system involvement and investigate subtle pathophysiological alterations in TSC patients.

PURPOSE

Here, we review the state-of-the-art knowledge in TSC brain imaging, describing conventional findings and depicting the role of advanced techniques in providing new insights on the disease, also offering an overview on future perspectives of neuroimaging applications for a better understanding of disease pathophysiology.

Tuberous Sclerosis Complex as Disease Model for Investigating mTOR-Related Gliopathy During Epileptogenesis

Tuberous sclerosis complex (TSC) represents the prototypic monogenic disorder of the mammalian target of rapamycin (mTOR) pathway dysregulation. It provides the rational mechanistic basis of a direct link between gene mutation and brain pathology (structural and functional abnormalities) associated with a complex clinical phenotype including epilepsy, autism, and intellectual disability. So far, research conducted in TSC has been largely neuron-oriented. However, the neuropathological hallmarks of TSC and other malformations of cortical development also include major morphological and functional changes in glial cells involving astrocytes, oligodendrocytes, NG2 glia, and microglia. These cells and their interglial crosstalk may offer new insights into the common neurobiological mechanisms underlying epilepsy and the complex cognitive and behavioral comorbidities that are characteristic of the spectrum of mTOR-associated neurodevelopmental disorders. This review will focus on the role of glial dysfunction, the interaction between glia related to mTOR hyperactivity, and its contribution to epileptogenesis in TSC. Moreover, we will discuss how understanding glial abnormalities in TSC might give valuable insight into the pathophysiological mechanisms that could help to develop novel therapeutic approaches for TSC or other pathologies characterized by glial dysfunction and acquired mTOR hyperactivation.

Autism and Epilepsy in Patients With Tuberous Sclerosis Complex

Introduction: Individuals with Tuberous Sclerosis Complex (TSC) are at increased risk of developing both epilepsy and autism spectrum disorder (ASD), but the relationship between these conditions is little understood. We reviewed published reports to elucidate the relationship between ASD, epilepsy, and TSC, and to define the genetic and neurological risk factors. Methods: Articles (January 2004-May 2019) were identified via PubMed, EMBASE, and CENTRAL databases. Article inclusion required report on individuals with TSC-associated ASD and epilepsy with prevalence, odds ratio, or rate report on the comorbidity of ASD in epileptic patients due to TSC. Results: A total of 841 abstracts were identified in the original search. Thirty-six articles were included, which identified study populations, ASD measures used, and study confounders as bias factors. This review included 2,666 TSC patients, with a mean age of 15.9 years (range 1.94-30.3 years). The percentage of TSC patients with epilepsy and autism was 33.7%. Patients with TSC and autism showed more frequent seizures and earlier epilepsy onset than TSC patients without autism. ASD and intractable epilepsy were both predicted by a higher number of areas with dysplastic features revealed in brain MR scans. ASD, the onset of seizures in children <2 years of age, and >3 tubers have all been associated with an increased risk of refractory epilepsy in TSC patients. However, the direction of the relationship is not clear because a history of epilepsy, or infantile spasms in patients with TSC is also associated with an increased likelihood of ASD. Overall, 73.2% of patients carried TSC2 genetic variant and, among patients with TSC and autism, the percentage of TSC2 individuals was 85.6%. Conclusions: The complex interrelationship between TSC, autism, and epilepsy, coupled with limited knowledge on the neurobiological basis for the interrelationship, limits overall understanding and opportunities for management. The results of this review highlight the need for early identification and management to optimize favorable outcomes in the most vulnerable individuals with TSC. Regardless of whether studies are considered individually or collectively, interpretation is made difficult due to the differences between the studies, most notably between methods and diagnostic criteria used to assess intellectual ability.

Early patterns of functional brain development associated with autism spectrum disorder in tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a rare genetic disorder that confers a high risk for autism spectrum disorders (ASD), with behavioral predictors of ASD emerging early in life. Deviations in structural and functional neural connectivity are highly implicated in both TSC and ASD. For the first time, we explore whether electroencephalographic (EEG) measures of neural network function precede or predict the emergence of ASD in TSC. We determine whether altered brain function (a) is present in infancy in TSC, (b) differentiates infants with TSC based on ASD diagnostic status, and (c) is associated with later cognitive function. We studied 35 infants with TSC (N = 35), and a group of typically developing infants (N = 20) at 12 and 24 months of age. Infants with TSC were later subdivided into ASD and non-ASD groups based on clinical evaluation. We measured features of spontaneous alpha oscillations (6-12 Hz) that are closely associated with neural network development: alpha power, alpha phase coherence (APC), and peak alpha frequency (PAF). Infants with TSC demonstrated reduced interhemispheric APC compared to controls at 12 months of age, and these differences were found to be most pronounced at 24 months in the infants who later developed ASD. Across all infants, PAF at 24 months was associated with verbal and nonverbal cognition at 36 months. Associations between early network function and later neurodevelopmental and cognitive outcomes highlight the potential utility of early scalable EEG markers to identify infants with TSC requiring additional targeted intervention initiated very early in life. Autism Res 2019, 12: 1758-1773. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Approximately half of infants with tuberous sclerosis complex (TSC) develop autism. Here, using EEG, we find that there is a reduction in communication between brain regions during infancy in TSC, and that the infants who show the largest reductions are those who later develop autism. Being able to identify infants who show early signs of disrupted brain development may improve the timing of early prediction and interventions in TSC, and also help us to understand how early brain changes lead to autism.

Longitudinal Effects of Everolimus on White Matter Diffusion in Tuberous Sclerosis Complex

OBJECTIVE

We studied the longitudinal effects of everolimus, an inhibitor of the mammalian target of rapamycin (mTOR), on callosal white matter diffusion tensor imaging (DTI) in patients with tuberous sclerosis complex (TSC).

METHODS

Serial imaging data spanning nine years were used from the open label, Phase I/II trial (NCT00411619) and open-ended extension phase of everolimus for the treatment of subependymal giant cell astrocytoma associated with TSC. From 28 patients treated with everolimus and 25 untreated control patients, 481 MRI scans were available. Rigorous quality control resulted in omission of all scans with diffusion weighted imaging data in less than 15 directions or more than eight artifacted volumes, and all postsurgical scans. We applied a linear mixed-effects model to the remaining 125 scans (17 treated, 24 controls) for longitudinal analysis of each DTI metric of manually drawn callosal regions of interest.

RESULTS

On a population level, mTOR inhibition was associated with a decrease in mean diffusivity. In addition, in treated patients only, a decrease of radial diffusivity was observed; in untreated patients only, an increase of axial diffusivity was seen. In patients below age 10, effect-sizes were consistently greater, and longer treatment was associated with greater rate of diffusion change. There was no correlation between DTI metrics and reduction of subependymal giant cell astrocytoma volume, or everolimus serum levels.

CONCLUSIONS

Effects from mTOR overactivity on white matter microstructural integrity in TSC were modified through pharmacologic inhibition of mTOR. These changes sustained over time, were greater with longer treatment and in younger patients during a time of rapid white matter maturation.

Corpus Callosum White Matter Diffusivity Reflects Cumulative Neurological Comorbidity in Tuberous Sclerosis Complex

INTRODUCTION

Neurological manifestations in Tuberous Sclerosis Complex (TSC) are highly variable. Diffusion tensor imaging (DTI) may reflect the neurological disease burden. We analyzed the association of autism spectrum disorder (ASD), intellectual disability (ID) and epilepsy with callosal DTI metrics in subjects with and without TSC.

METHODS

186 children underwent 3T MRI DTI: 51 with TSC (19 with concurrent ASD), 46 with non-syndromic ASD and 89 healthy controls (HC). Subgroups were based on presence of TSC, ASD, ID, and epilepsy. Density-weighted DTI metrics obtained from tractography of the corpus callosum were fitted using a 2-parameter growth model. We estimated distributions using bootstrapping and calculated half-life and asymptote of the fitted curves.

RESULTS

TSC was associated with a lower callosal fractional anisotropy (FA) than ASD, and ASD with a lower FA than HC. ID, epilepsy and ASD diagnosis were each associated with lower FA values, demonstrating additive effects. In TSC, the largest change in FA was related to a comorbid diagnosis of ASD. Mean diffusivity (MD) showed an inverse relationship to FA. Some subgroups were too small for reliable data fitting.

CONCLUSIONS

Using a cross-disorder approach, this study demonstrates cumulative abnormality of callosal white matter diffusion with increasing neurological comorbidity.

Applying the Lessons of Tuberous Sclerosis: The 2015 Hower Award Lecture

Tuberous sclerosis complex is a dominantly inherited disorder that variably affects the brain, skin, kidneys, heart, and other organs. Its neurological manifestations include epilepsy, autism, cognitive and behavioral dysfunction, and giant cell tumors. A mutation of either TSC1 or TSC2 can cause tuberous sclerosis complex. Their two gene products, hamartin and tuberin, form a physical complex which normally inhibits protein synthesis mediated through the mechanistic target of rapamycin, so a TSC1 or TSC2 mutation results in overactivation of the mechanistic target of rapamycin cascade. In addition to their tumor suppressor roles, TSC1 and TSC2 help to regulate cell size, neuronal migration, axon formation, and synaptic plasticity. Clinical trials of two different the mechanistic target of rapamycin inhibitors have demonstrated substantial improvement of tuberous sclerosis complex-related tumors, and a recent trial also showed a benefit from the mechanistic target of rapamycin inhibitor everolimus in the treatment of refractory epilepsy due to tuberous sclerosis complex. Effective mechanism-based therapy is now available for some manifestations of tuberous sclerosis complex.

mTORC1 Inhibition Corrects Neurodevelopmental and Synaptic Alterations in a Human Stem Cell Model of Tuberous Sclerosis

Hyperfunction of the mTORC1 pathway has been associated with idiopathic and syndromic forms of autism spectrum disorder (ASD), including tuberous sclerosis, caused by loss of either TSC1 or TSC2. It remains largely unknown how developmental processes and biochemical signaling affected by mTORC1 dysregulation contribute to human neuronal dysfunction. Here, we have characterized multiple stages of neurogenesis and synapse formation in human neurons derived from TSC2-deleted pluripotent stem cells. Homozygous TSC2 deletion causes severe developmental abnormalities that recapitulate pathological hallmarks of cortical malformations in patients. Both TSC2(+/-) and TSC2(-/-) neurons display altered synaptic transmission paralleled by molecular changes in pathways associated with autism, suggesting the convergence of pathological mechanisms in ASD. Pharmacological inhibition of mTORC1 corrects developmental abnormalities and synaptic dysfunction during independent developmental stages. Our results uncouple stage-specific roles of mTORC1 in human neuronal development and contribute to a better understanding of the onset of neuronal pathophysiology in tuberous sclerosis.

Neonatal Seizures: Impact on Neurodevelopmental Outcomes

Neonatal period is the most vulnerable time for the occurrence of seizures, and neonatal seizures often pose a clinical challenge both for their acute management and frequency of associated long-term co-morbidities. Etiologies of neonatal seizures are known to play a primary role in the anti-epileptic drug responsiveness and the long-term sequelae. Recent studies have suggested that burden of acute recurrent seizures in neonates may also impact chronic outcomes independent of the etiology. However, not many studies, either clinical or pre-clinical, have addressed the long-term outcomes of neonatal seizures in an etiology-specific manner. In this review, we briefly review the available clinical and pre-clinical research for long-term outcomes following neonatal seizures. As the most frequent cause of acquired neonatal seizures, we focus on the studies evaluating long-term effects of HIE-seizures with the goal to evaluate (1) what parameters evaluated during acute stages of neonatal seizures can reliably be used to predict long-term outcomes? and (2) what available clinical and pre-clinical data are available help determine importance of etiology vs. seizure burdens in long-term sequelae.