Survey of somatic mutations in tuberous sclerosis complex (TSC) hamartomas suggests different genetic mechanisms for pathogenesis of TSC lesions

TSC2 loss in neural progenitor cells suppresses translation of ASD/NDD-associated transcripts in an mTORC1- and MNK1/2-reversible fashion

Tuberous sclerosis complex (TSC) is an inherited neurodevelopmental disorder (NDD) with frequent manifestations of epilepsy and autism spectrum disorder (ASD). TSC is caused by inactivating mutations in TSC1 or TSC2 tumor suppressor genes, with encoded proteins hamartin (TSC1) and tuberin (TSC2) forming a functional complex inhibiting mechanistic target of rapamycin complex 1 (mTORC1) signaling. This has led to treatment with allosteric mTORC1 inhibitor rapamycin analogs ("rapalogs") for TSC tumors; however, rapalogs are ineffective for treating neurodevelopmental manifestations. mTORC1 signaling controls protein synthesis by regulating formation of the eIF4F complex, with further modulation by MNK1/2 kinases via phosphorylation of the eIF4F subunit eIF4E. While both these pathways modulate translation, comparing their impact on transcriptome-wide mRNA translation, as well as effects of inhibiting these pathways in TSC has not been explored. Here, employing CRISPR-modified, isogenic TSC2 patient-derived neural progenitor cells (NPCs), we have examined transcriptome-wide changes in mRNA translation upon TSC2 loss. Our results reveal dysregulated translation in TSC2 -Null NPCs, which significantly overlaps with the translatome from TSC1 -Null NPCs. Interestingly, numerous non-monogenic ASD-, NDD-and epilepsy-associated genes identified in patients harboring putative loss-of-function mutations, were translationally suppressed in TSC2 -Null NPCs. Importantly, translation of these ASD- and NDD-associated genes was reversed upon inhibition of either mTORC1 or MNK1/2 signaling using RMC-6272 or eFT-508, respectively. This study establishes the importance of mTORC1-eIF4F- and MNK-eIF4E-sensitive mRNA translation in TSC, ASD and other neurodevelopmental disorders laying the groundwork for evaluating drugs in clinical development that target these pathways as a treatment strategy for these disorders.

The clinical, imaging, pathological and genetic landscape of bottom-of-sulcus dysplasia

Bottom-of-sulcus dysplasia (BOSD) is increasingly recognized as a cause of drug-resistant, surgically-remediable, focal epilepsy, often in seemingly MRI-negative patients. We describe the clinical manifestations, morphological features, localization patterns and genetics of BOSD, with the aims of improving management and understanding pathogenesis. We studied 85 patients with BOSD diagnosed between 2005-2022. Presenting seizure and EEG characteristics, clinical course, genetic findings and treatment response were obtained from medical records. MRI (3 T) and 18F-FDG-PET scans were reviewed systematically for BOSD morphology and metabolism. Histopathological analysis and tissue genetic testing were performed in 64 operated patients. BOSD locations were transposed to common imaging space to study anatomical location, functional network localization and relationship to normal MTOR gene expression. All patients presented with stereotyped focal seizures with rapidly escalating frequency, prompting hospitalization in 48%. Despite 42% patients having seizure remissions, usually with sodium channel blocking medications, most eventually became drug-resistant and underwent surgery (86% seizure-free). Prior developmental delay was uncommon but intellectual, language and executive dysfunction were present in 24%, 48% and 29% when assessed preoperatively, low intellect being associated with greater epilepsy duration. BOSDs were missed on initial MRI in 68%, being ultimately recognized following repeat MRI, 18F-FDG-PET or image postprocessing. MRI features were grey-white junction blurring (100%), cortical thickening (91%), transmantle band (62%), increased cortical T1 signal (46%) and increased subcortical FLAIR signal (26%). BOSD hypometabolism was present on 18F-FDG-PET in 99%. Additional areas of cortical malformation or grey matter heterotopia were present in eight patients. BOSDs predominated in frontal and pericentral cortex and related functional networks, mostly sparing temporal and occipital cortex, and limbic and visual networks. Genetic testing yielded pathogenic mTOR pathway variants in 63% patients, including somatic MTOR variants in 47% operated patients and germline DEPDC5 or NPRL3 variants in 73% patients with familial focal epilepsy. BOSDs tended to occur in regions where the healthy brain normally shows lower MTOR expression, suggesting these regions may be more vulnerable to upregulation of MTOR activity. Consistent with the existing literature, these results highlight (i) clinical features raising suspicion of BOSD; (ii) the role of somatic and germline mTOR pathway variants in patients with sporadic and familial focal epilepsy associated with BOSD; and (iii) the role of 18F-FDG-PET alongside high-field MRI in detecting subtle BOSD. The anatomical and functional distribution of BOSDs likely explain their seizure, EEG and cognitive manifestations and may relate to relative MTOR expression.

The role of TSC1 and TSC2 proteins in neuronal axons

Tuberous Sclerosis Complex 1 and 2 proteins, TSC1 and TSC2 respectively, participate in a multiprotein complex with a crucial role for the proper development and function of the nervous system. This complex primarily acts as an inhibitor of the mechanistic target of rapamycin (mTOR) kinase, and mutations in either TSC1 or TSC2 cause a neurodevelopmental disorder called Tuberous Sclerosis Complex (TSC). Neurological manifestations of TSC include brain lesions, epilepsy, autism, and intellectual disability. On the cellular level, the TSC/mTOR signaling axis regulates multiple anabolic and catabolic processes, but it is not clear how these processes contribute to specific neurologic phenotypes. Hence, several studies have aimed to elucidate the role of this signaling pathway in neurons. Of particular interest are axons, as axonal defects are associated with severe neurocognitive impairments. Here, we review findings regarding the role of the TSC1/2 protein complex in axons. Specifically, we will discuss how TSC1/2 canonical and non-canonical functions contribute to the formation and integrity of axonal structure and function.

Activation of mTOR signaling in adult lung microvascular progenitor cells accelerates lung aging

Reactivation and dysregulation of the mTOR signaling pathway are a hallmark of aging and chronic lung disease; however, the impact on microvascular progenitor cells (MVPCs), capillary angiostasis, and tissue homeostasis is unknown. While the existence of an adult lung vascular progenitor has long been hypothesized, these studies show that Abcg2 enriches for a population of angiogenic tissue-resident MVPCs present in both adult mouse and human lungs using functional, lineage, and transcriptomic analyses. These studies link human and mouse MVPC-specific mTORC1 activation to decreased stemness, angiogenic potential, and disruption of p53 and Wnt pathways, with consequent loss of alveolar-capillary structure and function. Following mTOR activation, these MVPCs adapt a unique transcriptome signature and emerge as a venous subpopulation in the angiodiverse microvascular endothelial subclusters. Thus, our findings support a significant role for mTOR in the maintenance of MVPC function and microvascular niche homeostasis as well as a cell-based mechanism driving loss of tissue structure underlying lung aging and the development of emphysema.

Comprehensive genetic and phenotype analysis of 95 individuals with mosaic tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a neurogenetic disorder due to loss-of-function TSC1 or TSC2 variants, characterized by tumors affecting multiple organs, including skin, brain, heart, lung, and kidney. Mosaicism for TSC1 or TSC2 variants occurs in 10%-15% of individuals diagnosed with TSC. Here, we report comprehensive characterization of TSC mosaicism by using massively parallel sequencing (MPS) of 330 TSC samples from a variety of tissues and fluids from a cohort of 95 individuals with mosaic TSC. TSC1 variants in individuals with mosaic TSC are much less common (9%) than in germline TSC overall (26%) (p < 0.0001). The mosaic variant allele frequency (VAF) is significantly higher in TSC1 than in TSC2, in both blood and saliva (median VAF: TSC1, 4.91%; TSC2, 1.93%; p = 0.036) and facial angiofibromas (median VAF: TSC1, 7.7%; TSC2 3.7%; p = 0.004), while the number of TSC clinical features in individuals with TSC1 and TSC2 mosaicism was similar. The distribution of mosaic variants across TSC1 and TSC2 is similar to that for pathogenic germline variants in general TSC. The systemic mosaic variant was not present in blood in 14 of 76 (18%) individuals with TSC, highlighting the value of analysis of multiple samples from each individual. A detailed comparison revealed that nearly all TSC clinical features are less common in individuals with mosaic versus germline TSC. A large number of previously unreported TSC1 and TSC2 variants, including intronic and large rearrangements (n = 11), were also identified.

Specific Features of Focal Cortical Dysplasia in Tuberous Sclerosis Complex

Patients with tuberous sclerosis complex present with cognitive, behavioral, and psychiatric impairments, such as intellectual disabilities, autism spectrum disorders, and drug-resistant epilepsy. It has been shown that these disorders are associated with the presence of cortical tubers. Tuberous sclerosis complex results from inactivating mutations in the TSC1 or TSC2 genes, resulting in hyperactivation of the mTOR signaling pathway, which regulates cell growth, proliferation, survival, and autophagy. TSC1 and TSC2 are classified as tumor suppressor genes and function according to Knudson's two-hit hypothesis, which requires both alleles to be damaged for tumor formation. However, a second-hit mutation is a rare event in cortical tubers. This suggests that the molecular mechanism of cortical tuber formation may be more complicated and requires further research. This review highlights the issues of molecular genetics and genotype-phenotype correlations, considers histopathological characteristics and the mechanism of morphogenesis of cortical tubers, and also presents data on the relationship between these formations and the development of neurological manifestations, as well as treatment options.

Tsc2 mutation rather than Tsc1 mutation dominantly causes a social deficit in a mouse model of tuberous sclerosis complex

BACKGROUND

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that is associated with neurological symptoms, including autism spectrum disorder. Tuberous sclerosis complex is caused by pathogenic germline mutations of either the TSC1 or TSC2 gene, but somatic mutations were identified in both genes, and the combined effects of TSC1 and TSC2 mutations have been unknown.

METHODS

The present study investigated social behaviors by the social interaction test and three-chambered sociability tests, effects of rapamycin treatment, and gene expression profiles with a gene expression microarray in Tsc1 and Tsc2 double heterozygous mutant (TscD^+/-) mice.

RESULTS

TscD^+/- mice exhibited impairments in social behaviors, and the severity of impairments was similar to Tsc2^+/- mice rather than Tsc1^+/- mice. Impairments in social behaviors were rescued by rapamycin treatment in all mutant mice. Gene expression profiles in the brain were greatly altered in TscD^+/- mice more than in Tsc1^+/- and Tsc2^+/- mice. The gene expression changes compared with wild type (WT) mice were similar between TscD^+/- and Tsc2^+/- mice, and the overlapping genes whose expression was altered in mutant mice compared with WT mice were enriched in the neoplasm- and inflammation-related canonical pathways. The "signal transducer and activator of transcription 3, interferon regulatory factor 1, interferon regulatory factor 4, interleukin-2R α chain, and interferon-γ" signaling pathway, which is initiated from signal transducer and activator of transcription 4 and PDZ and LIM domain protein 2, was associated with impairments in social behaviors in all mutant mice.

LIMITATIONS

It is unclear whether the signaling pathway also plays a critical role in autism spectrum disorders not caused by Tsc1 and Tsc2 mutations.

CONCLUSIONS

These findings suggest that TSC1 and TSC2 double mutations cause autistic behaviors similarly to TSC2 mutations, although significant changes in gene expression were attributable to the double mutations. These findings contribute to the knowledge of genotype-phenotype correlations in TSC and suggest that mutations in both the TSC1 and TSC2 genes act in concert to cause neurological symptoms, including autism spectrum disorder.

Incidental finding of tuberous sclerosis complex in a woman with hematuria: A case report of renal angiomyolipoma and review of the literature

Tuberous sclerosis complex (TSC) is a rare genetic multisystem disorder that was first described by Von Recklinghausen. We describe a case of a female, who initially presented with hematuria and was later found to have multiple manifestations of the disease. The report emphasizes the value of investigations on suspected cases.

Genotype and Phenotype Landscape of 283 Japanese Patients with Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by multiple dysplastic organ lesions and neuropsychiatric symptoms, caused by loss of function mutations in either TSC1 or TSC2. Genotype and phenotype analyses are conducted worldwide, but there have been few large-scale studies on Japanese patients, and there are still many unclear points. This study analyzed 283 Japanese patients with TSC (225 definite, 53 possible, and 5 genetic diagnoses). A total of 200 mutations (64 TSC1, 136 TSC2) were identified, of which 17 were mosaic mutations, 11 were large intragenic deletions, and four were splicing abnormalities due to deep intronic mutations. Several lesions and symptoms differed in prevalence and severity between TSC1 and TSC2 patients and were generally more severe in TSC2 patients. Moreover, TSC2 missense and in-frame mutations may attenuate skin and renal symptoms compared to other TSC2 mutations. Genetic testing revealed that approximately 20% of parents of a proband had mild TSC, which could have been missed. The patient demographics presented in this study revealed a high frequency of TSC1 patients and a low prevalence of epilepsy compared to global statistics. More patients with mild neuropsychiatric phenotypes were diagnosed in Japan, seemingly due to a higher utilization of brain imaging, and suggesting the possibility that a significant amount of mild TSC patients may not be correctly diagnosed worldwide.

Ultrasensitive profiling of UV-induced mutations identifies thousands of subclinical facial tumors in tuberous sclerosis complex

BackgroundTuberous sclerosis complex (TSC) is a neurogenetic syndrome due to loss-of-function mutations in TSC2 or TSC1, characterized by tumors at multiple body sites, including facial angiofibroma (FAF). Here, an ultrasensitive assessment of the extent and range of UV-induced mutations in TSC facial skin was performed.MethodsA multiplex high-sensitivity PCR assay (MHPA) was developed, enabling mutation detection at extremely low (<0.1%) variant allele frequencies (VAFs).ResultsMHPA assays were developed for both TSC2 and TP53, and applied to 81 samples, including 66 skin biopsies. UV-induced second-hit mutation causing inactivation of TSC2 was pervasive in TSC facial skin with an average of 4.8 mutations per 2-mm biopsy at median VAF 0.08%, generating more than 150,000 incipient facial tumors (subclinical "micro-FAFs") in the average TSC subject. The MHPA analysis also led to the identification of a refined UV-related indel signature and a recurrent complex mutation pattern, consisting of both a single-nucleotide or dinucleotide variant and a 1- to 9-nucleotide deletion, in cis.ConclusionTSC facial skin can be viewed as harboring a patchwork of clonal fibroblast proliferations (micro-FAFs) with indolent growth, a small proportion of which develop into clinically observable FAF. Our observations also expand the spectrum of UV-related mutation signatures.FundingThis work was supported by the TSC Alliance; the Engles Family Fund for Research in TSC and LAM; and the NIH, National Heart, Lung, and Blood Institute (U01HL131022-04 and Intramural Research Program).

Cortical Dysplasia and the mTOR Pathway: How the Study of Human Brain Tissue Has Led to Insights into Epileptogenesis

Type II focal cortical dysplasia (FCD) is a neuropathological entity characterised by cortical dyslamination with the presence of dysmorphic neurons only (FCDIIA) or the presence of both dysmorphic neurons and balloon cells (FCDIIB). The year 2021 marks the 50th anniversary of the recognition of FCD as a cause of drug resistant epilepsy, and it is now the most common reason for epilepsy surgery. The causes of FCD remained unknown until relatively recently. The study of resected human FCD tissue using novel genomic technologies has led to remarkable advances in understanding the genetic basis of FCD. Mechanistic parallels have emerged between these non-neoplastic lesions and neoplastic disorders of cell growth and differentiation, especially through perturbations of the mammalian target of rapamycin (mTOR) signalling pathway. This narrative review presents the advances through which the aetiology of FCDII has been elucidated in chronological order, from recognition of an association between FCD and the mTOR pathway to the identification of somatic mosaicism within FCD tissue. We discuss the role of a two-hit mechanism, highlight current challenges and future directions in detecting somatic mosaicism in brain and discuss how knowledge of FCD may inform novel precision treatments of these focal epileptogenic malformations of human cortical development.

Mechanistic target of rapamycin signaling in human nervous system development and disease

Mechanistic target of rapamycin (mTOR) is a highly conserved serine/threonine kinase that regulates fundamental cellular processes including growth control, autophagy and metabolism. mTOR has key functions in nervous system development and mis-regulation of mTOR signaling causes aberrant neurodevelopment and neurological diseases, collectively called mTORopathies. In this mini review we discuss recent studies that have deepened our understanding of the key roles of the mTOR pathway in human nervous system development and disease. Recent advances in single-cell transcriptomics have been exploited to reveal specific roles for mTOR signaling in human cortical development that may have contributed to the evolutionary divergence from our primate ancestors. Cerebral organoid technology has been utilized to show that mTOR signaling is active in and regulates outer radial glial cells (RGCs), a population of neural stem cells that distinguish the human developing cortex. mTOR signaling has a well-established role in hamartoma syndromes such as tuberous sclerosis complex (TSC) and other mTORopathies. New ultra-sensitive techniques for identification of somatic mTOR pathway mutations have shed light on the neurodevelopmental origin and phenotypic heterogeneity seen in mTORopathy patients. These emerging studies suggest that mTOR signaling may facilitate developmental processes specific to human cortical development but also, when mis-regulated, cause cortical malformations and neurological disease.

Diagnostic features of tuberous sclerosis complex: case report and literature review

Tuberous sclerosis complex (TSC) is a rare autosomal dominant genetic syndrome that is caused by mutations in the tumour suppressor genes TSC1 or TSC2 which causes multiorgan growths. TSC presents at any age as a wide range of clinical and phenotypic manifestations with varying severity. The main goal of this article was to state two cases of TSC and review the most commonly reported major and minor diagnostic clinical features and the most common features that led to an investigation of possible TSC diagnosis. Herein, we report two cases of TSC, which both presented with seizures during the first 6 months of life. Case 1 presented with multiple types of seizures from 6 months of age and was diagnosed by multiple calcified subependymal nodules (SENs) detected by computed tomography and magnetic resonance imaging (MRI). Case 2 presented with seizures from 3 months of age and was diagnosed prenatally when a tumour was seen in her heart during antenatal ultrasonography. In conclusion, the literature review revealed that neurological manifestations (mainly seizures) were the main feature that led to investigation and diagnosis of TSC followed by abdominal manifestations (mainly renal features) and antenatal follow-up imaging. Other manifestations in skin, chest, eyes, teeth and heart rarely led to TSC diagnosis. In some cases, TSC was incidentally discovered by medical imaging. The cortical tubers, SENs, and subependymal giant cell astrocytomas brain lesions were the most commonly reported major features. Skin features including angiofibromas, ungual fibromas and shagreen patch were the second most common major features reported in the literature. However, skin manifestations were not a common led to investigation and diagnosis of TSC. Renal features, mainly angiomyolipomas (AMLs), were the third most common major feature reported. Medical imaging plays an essential role in diagnosis of TSC, and clinical features are important clues that lead to investigation for the disease.

Resolution of multifocal micronodular pneumocyte hyperplasia with everolimus in a patient with tuberous sclerosis complex

A woman with a diagnosis of tuberous sclerosis complex (TSC) presented with TSC2 gene mutation and various manifestations, including epilepsy, renal angiomyolipomas (AML), and pathologically confirmed multifocal micronodular pneumocyte hyperplasia (MMPH). With oral administration of everolimus, a mammalian target of rapamycin (mTOR) inhibitor, MMPH and AML were markedly reduced. Further, after starting treatment with everolimus, serum levels of surfactant protein (SP)-A and SP-D, which reflect type II pneumocyte hyperplasia, decreased to the normal range. At the time of writing of this manuscript, 6 years after starting everolimus, MMPH lesions did not relapse and SP-A/D remained the low levels. This is the first case of everolimus efficacy shown for histologically confirmed MMPH in genetically determined TSC patient, with time course of serum SP-A and SP-D.

Sporadic facial angiofibroma and sporadic angiomyolipoma mimicking tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a genetic syndrome due to mutations in either TSC1 or TSC2, leading to the development of hamartomatous tumours at multiple body sites, including facial skin (facial angiofibroma (FAF)), brain (cortical tubers) and kidney (angiomyolipoma (AML)). In this report, we describe an individual with minimal TSC clinical features, who had 'no mutation identified' (NMI) by prior genetic testing in a clinical laboratory. Our massively parallel sequencing (MPS) analysis of multiple samples from different body sites and tumours (including blood, saliva, normal skin, AML and FAF) revealed an extraordinary situation in which FAF and AML had completely independent inactivating biallelic variants in TSC2, not present in other matched samples. This suggests that the two different lesions (AML and FAF) are not due to the same underlying germline or mosaic mutation, rather both are likely sporadic events. This case demonstrates the relevance of thorough clinical examination, high-coverage MPS of multiple tumours and matched normal tissues, and appropriate genetic counselling for individuals with marginal TSC features and possible TSC1 or TSC2 mosaicism.

Renal neoplasms in tuberous sclerosis mice are neurocristopathies

Tuberous sclerosis (TS) is a rare disorder exhibiting multi-systemic benign neoplasms. We hypothesized the origin of TS neoplastic cells derived from the neural crest given the heterogeneous ecto-mesenchymal phenotype of the most common TS neoplasms. To test this hypothesis, we employed Cre-loxP lineage tracing of myelin protein zero (Mpz)-expressing neural crest cells (NCCs) in spontaneously developing renal tumors of Tsc2 +/- /Mpz(Cre)/TdT fl/fl reporter mice. In these mice, ectopic renal tumor onset was detected at 4 months of age increasing in volume by 16 months of age with concomitant increase in the subpopulation of tdTomato+ NCCs from 0% to 6.45% of the total number of renal tumor cells. Our results suggest that Tsc2 +/- mouse renal tumors arise from domiciled proliferative progenitor cell populations of neural crest origin that co-opt tumorigenesis due to mutations in Tsc2 loci. Targeting neural crest antigenic determinants will provide a potential alternative therapeutic approach for TS pathogenesis.

Tsc Gene Locus Disruption and Differences in Renal Epithelial Extracellular Vesicles

In tuberous sclerosis complex (TSC), Tsc2 mutations are associated with more severe disease manifestations than Tsc1 mutations and the role of extracellular vesicles (EVs) in this context is not yet studied. We report a comparative analysis of EVs derived from isogenic renal cells except for Tsc1 or Tsc2 gene status and hypothesized that in spite of having similar physical characteristics, EVs modulate signaling pathways differently, thus leading to TSC heterogenicity. We used mouse inner medullary collecting duct (mIMCD3) cells with the Tsc1 (T1G cells) or Tsc2 (T2J cells) gene disrupted by CRISPR/CAS9. EVs were isolated from the cell culture media by size-exclusion column chromatography followed by detailed physical and chemical characterization. Physical characterization of EVs was accessed by tunable resistive pulse sensing and dynamic light scattering, revealing similar average sizes and zeta potentials (at pH 7.4) for EVs from mIMCD3 (123.5 ± 5.7 nm and −16.3 ± 2.1 mV), T1G cells (131.5 ± 8.3 nm and −19.8 ± 2.7 mV), and T2J cells (127.3 ± 4.9 nm and −20.2 ± 2.1 mV). EVs derived from parental mIMCD3 cells and both mutated cell lines were heterogeneous (>90% of EVs < 150 nm) in nature. Immunoblotting detected cilial Hedgehog signaling protein Arl13b; intercellular proteins TSG101 and Alix; and transmembrane proteins CD63, CD9, and CD81. Compared to Tsc2 deletion, Tsc1 deletion cells had reduced EV production and release rates. EVs from Tsc1 mutant cells altered mTORC1, autophagy, and β-catenin pathways differently than EVs from Tsc2-mutated cells. Quantitative PCR analysis revealed the down regulation of miR-212a-3p and miR-99a-5p in EVs from Tsc2-mutated cells compared to EVs from Tsc1-mutant cells. Thus, EV-derived miR-212-3p and mIR-99a-5p axes may represent therapeutic targets or biomarkers for TSC disease.

Brain Symptoms of Tuberous Sclerosis Complex: Pathogenesis and Treatment

The mammalian target of the rapamycin (mTOR) system plays multiple, important roles in the brain, regulating both morphology, such as cellular size, shape, and position, and function, such as learning, memory, and social interaction. Tuberous sclerosis complex (TSC) is a congenital disorder caused by a defective suppressor of the mTOR system, the TSC1/TSC2 complex. Almost all brain symptoms of TSC are manifestations of an excessive activity of the mTOR system. Many children with TSC are afflicted by intractable epilepsy, intellectual disability, and/or autism. In the brains of infants with TSC, a vicious cycle of epileptic encephalopathy is formed by mTOR hyperactivity, abnormal synaptic structure/function, and excessive epileptic discharges, further worsening epilepsy and intellectual/behavioral disorders. Molecular target therapy with mTOR inhibitors has recently been proved to be efficacious for epilepsy in human TSC patients, and for autism in TSC model mice, indicating the possibility for pharmacological treatment of developmental synaptic disorders.

Customized Targeted Massively Parallel Sequencing Enables More Precisely Diagnosis of Patients with Epilepsy

BACKGROUND

Advancement in genetic technology has led to the identification of an increasing number of genes in epilepsy. This will provide a huge information in clinical practice and improve diagnosis and treatment of epilepsy.

METHODS

this was a single-center retrospective cohort study of 80 patients who underwent NGS testing with customize epilepsy panel.

RESULTS

In total 54 out of 80 patients (67, 5%), pathogenic / likely pathogenic and variants of uncertain significance variants were identified according to ACMG criteria. Pathogenic or likely pathogenic variants (n=35) were identified in 29 out of 80 individuals (36.25%). Variants of uncertain significance (VOUS) (n=34) have identified in 28 out of 80 patients (35%). Pathogenic, likely pathogenic, and variants of uncertain significance (VOUS) were most frequently identified in TSC2 (n = 11), SCN1A (n = 6) and TSC1 (n = 5) genes. Other common genes were KCNQ2 (n = 3), AMT (n = 3), CACNA1H (n = 3), CLCN2 (n = 3), MECP2 (n = 2), ASAH1 (n = 2) and SLC2A1 (n = 2).

CONCLUSIONS

NGS based testing panels contributes the diagnosis of epilepsy and may change the clinical management by preventing unnecessary and potentially harmful diagnostic procedures and management in patients. Thus, our results highlighted the benefit of genetic testing in children suffered with epilepsy. This article is protected by copyright. All rights reserved.

Optimization and Validation of Multimodular, Long-Range PCR-Based Next-Generation Sequencing Assays for Comprehensive Detection of Mutation in Tuberous Sclerosis Complex

The genetic diagnosis of tuberous sclerosis complex is difficult because of its broad spectrum of mutations. In addition to point mutations in coding regions, intragenic or chromosomal-level large deletions, deep intronic splicing mutations, and mosaic mutations represent a significant proportion of the mutations. In this study, multimodular, long-range PCR-based next-generation sequencing assays were optimized and validated using >100 samples with known TSC1 and TSC2 variants. Multiplex, long-range PCR covering the entire genomic region of both genes detected all 138 known variants; however, it also yielded false-positive results. Intragenic large deletions were detected with accurate breakpoint sequences. Chromosomal-level deletions were estimated by discordant allele segregation in the family and confirmed by DNA microarray. Deep intronic mutations were verified using a combination of long-range DNA PCR and full-length mRNA sequencing. DNA samples were mixed to simulate mosaic mutations, and most variants were detected but could not be distinguished from equivalently detected false-positive results. Repeated false-positive results were classified, and the strategy of selecting the common variants detected in the duplicate analysis and eliminating known false-positive results improved the sensitivity (85.2%) and positive predictive value (96.6%) of a 10% mosaic simulation. Long-range PCRbased next-generation sequencing is a highly versatile genetic test; however, confirmation tests remain necessary for clinical use because false-positive results cannot be completely eliminated from single experiments.

The Neurodevelopmental Pathogenesis of Tuberous Sclerosis Complex (TSC)

Tuberous sclerosis complex (TSC) is a model disorder for understanding brain development because the genes that cause TSC are known, many downstream molecular pathways have been identified, and the resulting perturbations of cellular events are established. TSC, therefore, provides an intellectual framework to understand the molecular and biochemical pathways that orchestrate normal brain development. The TSC1 and TSC2 genes encode Hamartin and Tuberin which form a GTPase activating protein (GAP) complex. Inactivating mutations in TSC genes (TSC1/TSC2) cause sustained Ras homologue enriched in brain (RHEB) activation of the mammalian isoform of the target of rapamycin complex 1 (mTORC1). TOR is a protein kinase that regulates cell size in many organisms throughout nature. mTORC1 inhibits catabolic processes including autophagy and activates anabolic processes including mRNA translation. mTORC1 regulation is achieved through two main upstream mechanisms. The first mechanism is regulation by growth factor signaling. The second mechanism is regulation by amino acids. Gene mutations that cause too much or too little mTORC1 activity lead to a spectrum of neuroanatomical changes ranging from altered brain size (micro and macrocephaly) to cortical malformations to Type I neoplasias. Because somatic mutations often underlie these changes, the timing, and location of mutation results in focal brain malformations. These mutations, therefore, provide gain-of-function and loss-of-function changes that are a powerful tool to assess the events that have gone awry during development and to determine their functional physiological consequences. Knowledge about the TSC-mTORC1 pathway has allowed scientists to predict which upstream and downstream mutations should cause commensurate neuroanatomical changes. Indeed, many of these predictions have now been clinically validated. A description of clinical imaging and histochemical findings is provided in relation to laboratory models of TSC that will allow the reader to appreciate how human pathology can provide an understanding of the fundamental mechanisms of development.

High Mobility Group AT-Hook 2 (HMGA2) Oncogenicity in Mesenchymal and Epithelial Neoplasia

High mobility group AT-hook 2 (HMGA2) has been associated with increased cell proliferation and cell cycle dysregulation, leading to the ontogeny of varied tumor types and their metastatic potentials, a frequently used index of disease prognosis. In this review, we deepen our understanding of HMGA2 pathogenicity by exploring the mechanisms by which HMGA2 misexpression and ectopic expression induces mesenchymal and epithelial tumorigenesis respectively and distinguish the pathogenesis of benign from malignant mesenchymal tumors. Importantly, we highlight the regulatory role of let-7 microRNA family of tumor suppressors in determining HMGA2 misexpression events leading to tumor pathogenesis and focused on possible mechanisms by which HMGA2 could propagate lymphangioleiomyomatosis (LAM), benign mesenchymal tumors of the lungs. Lastly, we discuss potential therapeutic strategies for epithelial and mesenchymal tumorigenesis based on targeting the HMGA2 signaling pathway.

Precise detection of low-level somatic mutation in resected epilepsy brain tissue

Low-level somatic mutations have been shown to be the major genetic etiology of intractable epilepsy. The extents thereof, however, have yet to be systematically and accurately explored in a large cohort of resected epilepsy brain tissues. Moreover, clinically useful and precise analysis tools for detecting low-level somatic mutations from unmatched formalin-fixed paraffin-embedded (FFPE) brain samples, the most clinically relevant samples, are still lacking. In total, 446 tissues samples from 232 intractable epilepsy patients with various brain pathologies were analyzed using deep sequencing (average read depth, 1112x) of known epilepsy-related genes (up to 28 genes) followed by confirmatory site-specific amplicon sequencing. Pathogenic mutations were discovered in 31.9% (74 of 232) of the resected epilepsy brain tissues and were recurrently found in only eight major focal epilepsy genes, including AKT3, DEPDC5, MTOR, PIK3CA, TSC1, TSC2, SCL35A2, and BRAF. Somatic mutations, two-hit mutations, and germline mutations accounted for 22.0% (51), 0.9% (2), and 9.1% (21) of the patients with intractable epilepsy, respectively. The majority of pathogenic somatic mutations (62.3%, 33 of 53) had a low variant allelic frequency of less than 5%. The use of deep sequencing replicates in the eight major focal epilepsy genes robustly increased PPVs to 50-100% and sensitivities to 71-100%. In an independent FCDII cohort of only unmatched FFPE brain tissues, deep sequencing replicates in the eight major focal epilepsy genes identified pathogenic somatic mutations in 33.3% (5 of 15) of FCDII individuals (similar to the genetic detecting rate in the entire FCDII cohort) without any false-positive calls. Deep sequencing replicates of major focal epilepsy genes in unmatched FFPE brain tissues can be used to accurately and efficiently detect low-level somatic mutations, thereby improving overall patient care by enriching genetic counseling and informing treatment decisions.

Pancreatic Neuroendocrine Tumor in a Young Child With Tuberous Sclerosis Complex 1

Pancreatic neuroendocrine tumors (PNETs) occur in the context of tuberous sclerosis complex (TSC). To date, PNETs in association with TSC have been described almost exclusively in adults and in the context of TSC2. We present the evaluation of a PNET in a young child with TSC1. A 3-year, 6-month-old boy with TSC1 was found on surveillance to have a small pancreatic lesion measuring 0.4 cm on magnetic resonance imaging (MRI). The lesion showed interval enlargement to 1 cm on serial MRI studies during the ensuing 16 weeks. Endocrine laboratory tests did not reveal a functional tumor. The patient underwent enucleation of the pancreatic lesion. Microscopic examination defined a well-differentiated PNET, grade II/intermediate grade with a mitotic rate of two mitotic figures per 10 high-powered field and Ki-67 proliferation index of ∼15%. The tumor was positive for the TSC1 gene mutation. The patient was free of tumor recurrence at the 5-year follow-up examination, as determined by endocrine surveillance and annual MRI of the abdomen. In the reported data, PNET in patients with TSC has been primarily reported in association with TSC2. Our case demonstrates that patients with TSC1 can develop PNETs, even at an early age. The international TSC consensus group 2012 recommendation was to obtain MRI of the abdomen every 1 to 3 years for surveillance of renal angiomyolipomas and renal cystic disease. It might be beneficial to add a pancreatic protocol to the surveillance guidelines to evaluate for PNET.

Familial multifocal micronodular pneumocyte hyperplasia with a novel splicing mutation in TSC1: Three cases in one family

Multifocal micronodular pneumocyte hyperplasia (MMPH) is a rare pulmonary disease, generally manifesting as a tuberous sclerosis complex (TSC), characterised by multiple, small ground-glass nodular shadows on chest computed tomography (CT). Histological examination typically reveals multicentric, well-demarcated, nodular type II pneumocystic growth. Herein, we describe three cases of this rare pulmonary disease occurring within one family. Using reverse transcription polymerase chain reaction (RT-PCR) and direct DNA sequencing, we identified a novel germline mutation, a point mutation in TSC1 intron 5, which yielded a splice variant and loss of function of TSC1. Furthermore, immunohistochemical staining indicated the expression of phospho-p70S6K and phospho-4E-BP1, suggesting that TSC1 function was impaired by the novel gene mutation in MMPH cells.

Pulmonary manifestations in tuberous sclerosis complex

Tuberous sclerosis complex has manifestations in many organ systems, including brain, heart, kidney, skin, and lung. The primary manifestations in the lung are lymphangioleiomyomatosis (LAM) and multifocal micronodular pneumocyte hyperplasia (MMPH). LAM affects almost exclusively women, and causes cystic lung destruction, pneumothorax, and chylous pleural effusions. LAM can lead to dyspnea, oxygen dependence, and respiratory failure, with more rapid disease progression during the premenopausal years. In contrast, MMPH affects men and women equally, causing small nodular pulmonary deposits of type II pneumocytes that rarely progress to symptomatic disease. Here, we review the clinical features and pathogenesis of LAM and MMPH.

Human renal angiomyolipoma cells of male and female origin can migrate and are influenced by microenvironmental factors

Background

Improving the knowledge of angiomyolipoma physiopathology might help in refining its pharmacological treatment. We investigated if angiomyolipoma cells have migratory properties, how their growth and motility can be influenced by the hormonal milieu, and if this can be related to a specific gender.

Methods

Primary cells were isolated from angiomyolipomas surgically resected for therapeutical reasons in a female and in a male patient. The genetic control demonstrated no TSC2 deletion. Bi- (wound healing) and three-dimensional (transwell assay) migration were analyzed in vitro in basal conditions and under the influence of 17- β-estradiol and SDF-1α.

Results

Treatment up to 72 hours with 17-β-estradiol (0.1–100 nM), tamoxifen (0.2–20 μM) or with both, does not modify angiomyolipoma cells proliferation. On the other hand, SDF-1α and 17-β-estradiol treatment induce a significant motility increase (both bi- and three-dimensional) which becomes evident already after 2 hours of incubation. Angiomyolipoma cells express mRNA coding for SDF-1α and 17-β-estradiol receptors and secrete both the metalloproteases principally involved in malignant phenotype acquisition, i.e. MMP-2 and MMP-9.

Conclusion

Angiomyolipoma cells behave similarly, despite their different source. Primary angiomyolipoma cells migrate in response to hormonal milieu and soluble factors, and produce active metalloproteases, both aspects being consistent with the theory claiming they can migrate to the lungs (and/or other organs) and colonizing them. No main feature, among the aspects we analyzed, seems to be referable to the gender of origin.

A Novel Mutation in TSC2 Gene: A 34-Year-Old Female with Pulmonary Lymphangioleiomyomatosis with Concomitant Hepatic Lesions

Tuberous sclerosis complex (TSC) is an autosomal dominant disease resulting from mutation(s) in TSC1 or TSC2 genes. TSC is associated with the formation of hamartomas in the brain, heart, eyes, skin, kidneys, and lymphangioleiomyomatosis (LAM) of the lungs. LAM is almost restricted to women in reproductive age. Different mutations in TSC1 and TSC2 genes have been reported in the literature. Here, we present a female patient with TSC-LAM with a novel mutation in TSC2 gene. The patient also had multiple hepatic angiomyolipomas, which is a relatively less-reported manifestation of the disease. The impact of this mutation on the pattern of disease presentation and response to treatment is not clear yet.

Heterozygous loss of TSC2 alters p53 signaling and human stem cell reprogramming

Tuberous sclerosis complex (TSC) is a pediatric disorder of dysregulated growth and differentiation caused by loss of function mutations in either the TSC1 or TSC2 genes, which regulate mTOR kinase activity. To study aberrations of early development in TSC, we generated induced pluripotent stem cells using dermal fibroblasts obtained from patients with TSC. During validation, we found that stem cells generated from TSC patients had a very high rate of integration of the reprogramming plasmid containing a shRNA against TP53. We also found that loss of one allele of TSC2 in human fibroblasts is sufficient to increase p53 levels and impair stem cell reprogramming. Increased p53 was also observed in TSC2 heterozygous and homozygous mutant human stem cells, suggesting that the interactions between TSC2 and p53 are consistent across cell types and gene dosage. These results support important contributions of TSC2 heterozygous and homozygous mutant cells to the pathogenesis of TSC and the important role of p53 during reprogramming.

The genomic landscape of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a rare genetic disease causing multisystem growth of benign tumours and other hamartomatous lesions, which leads to diverse and debilitating clinical symptoms. Patients are born with TSC1 or TSC2 mutations, and somatic inactivation of wild-type alleles drives MTOR activation; however, second hits to TSC1/TSC2 are not always observed. Here, we present the genomic landscape of TSC hamartomas. We determine that TSC lesions contain a low somatic mutational burden relative to carcinomas, a subset feature large-scale chromosomal aberrations, and highly conserved molecular signatures for each type exist. Analysis of the molecular signatures coupled with computational approaches reveals unique aspects of cellular heterogeneity and cell origin. Using immune data sets, we identify significant neuroinflammation in TSC-associated brain tumours. Taken together, this molecular catalogue of TSC serves as a resource into the origin of these hamartomas and provides a framework that unifies genomic and transcriptomic dimensions for complex tumours.

Genetics of tuberous sclerosis complex: implications for clinical practice

Tuberous sclerosis complex (TSC) is a multisystem disorder that results from heterozygous mutations in either TSC1 or TSC2. The primary organ systems that are affected include the brain, skin, lung, kidney, and heart, all with variable frequency, penetrance, and severity. Neurological features include epilepsy, autism, and intellectual disability. There are more than 1,500 known pathogenic variants for TSC1 and TSC2, including deletion, nonsense, and missense mutations, and all pathogenic mutations are inactivating, leading to loss of function effects on the encoded proteins TSC1 and TSC2. These proteins form a complex to constitutively inhibit mechanistic target of rapamycin (mTOR) signaling cascade, and as a consequence, mTOR signaling is constitutively active within all TSC-associated lesions. The mTOR inhibitors rapamycin (sirolimus) and everolimus have been shown to reduce the size of renal and brain lesions and improve pulmonary function in TSC, and these compounds may also decrease seizure frequency. The clinical application of mTOR inhibitors in TSC has provided one of the first examples of precision medicine in a neurodevelopmental disorder.

Genotype/Phenotype Correlations in Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by the development of widespread hamartomatous lesions in various organs, including brain, skin, kidneys, heart, and eyes. Central nervous system is almost invariably involved, with up to 85% of patients presenting with epilepsy, and at least half of patients having intellectual disability or other neuropsychiatric disorders including autism spectrum disorder. TSC is caused by the mutation in one of the 2 genes TSC1, at 9q34, and TSC2, at 16p13.3. They respectively encode for hamartin and tuberin, which form an intracellular complex inhibiting the mammalian target of rapamycin. Mammalian target of rapamycin overactivation following the genetic defect determines the cell growth and proliferation responsible for TSC-related lesions, as well as the alterations in neuronal excitability and synaptogenesis leading to epilepsy and neuropsychiatric disorders. A causative mutation for the disorder is identified in about 85% of patients with a clinical diagnosis of TSC. Mosaicism and technology limits likely explain most of the no mutation identified cases. This review confirms that patients with TSC2 mutations considered as a group usually present a more severe phenotype, characterized by higher number of tubers, earlier age at seizure onset and higher prevalence of intellectual disability. However, the clinical phenotype of the disease presents a high variability, thus making the prediction of the phenotype on an individual basis still challenging. The increasing application of new molecular techniques to subjects with TSC has the potential to significantly reduce the rate of patients with no mutation demonstrated and to identify an increasing higher number of mutations. This would hopefully allow a better characterization of higher risk mutations, which might help clinicians to plan individualized surveillance plans. Furthermore, the increasing availability of disease registries to collect clinical and genetics data of patients help to define more valid and clinically oriented genotype or phenotype correlations.

Epileptic spasms are a feature of DEPDC5 mTORopathy

Objective:

To assess the presence of DEPDC5 mutations in a cohort of patients with epileptic spasms.

Methods:

We performed DEPDC5 resequencing in 130 patients with spasms, segregation analysis of variants of interest, and detailed clinical assessment of patients with possibly and likely pathogenic variants.

Results:

We identified 3 patients with variants in DEPDC5 in the cohort of 130 patients with spasms. We also describe 3 additional patients with DEPDC5 alterations and epileptic spasms: 2 from a previously described family and a third ascertained by clinical testing. Overall, we describe 6 patients from 5 families with spasms and DEPDC5 variants; 2 arose de novo and 3 were familial. Two individuals had focal cortical dysplasia. Clinical outcome was highly variable.

Conclusions:

While recent molecular findings in epileptic spasms emphasize the contribution of de novo mutations, we highlight the relevance of inherited mutations in the setting of a family history of focal epilepsies. We also illustrate the utility of clinical diagnostic testing and detailed phenotypic evaluation in characterizing the constellation of phenotypes associated with DEPDC5 alterations. We expand this phenotypic spectrum to include epileptic spasms, aligning DEPDC5 epilepsies more with the recognized features of other mTORopathies.

Animal models of tumour-associated epilepsy

Brain tumours cause a sizeable proportion of epilepsies in adulthood, and actually can be etiologically responsible also for childhood epilepsies. Conversely, seizures are often first clinical signs of a brain tumour. Nevertheless, several issues of brain-tumour associated seizures and epilepsies are far from understood, or clarified regarding clinical consensus. These include both the specific mechanisms of epileptogenesis related to different tumour types, the possible relationship between malignancy and seizure emergence, the interaction between tumour mass and surrounding neuronal networks, and - not least - the best treatment options depending on different tumour types. To investigate these issues, experimental models of tumour-induced epilepsies are necessary. This review concentrates on the description of currently used models, focusing on methodological aspects. It highlights advantages and shortcomings of these models, and identifies future experimental challenges.

Infantile tauopathies: Hemimegalencephaly; tuberous sclerosis complex; focal cortical dysplasia 2; ganglioglioma

Tau is a normal microtubule-associated protein; mutations to phosphorylated or acetylated forms are neurotoxic. In many dementias of adult life tauopathies cause neuronal degeneration. Four developmental disorders of the fetal and infant brain are presented, each of which exhibits up-regulation of tau. Microtubules are cytoskeletal structures that provide the strands of mitotic spindles and specify cellular polarity, growth, lineage, differentiation, migration and axonal transport of molecules. Phosphorylated tau is abnormal in immature as in mature neurons. Several malformations are demonstrated in which upregulated tau may be important in pathogenesis. All produce highly epileptogenic cortical foci. The prototype infantile tauopathy is (1) hemimegalencephaly (HME); normal tau is degraded by a mutant AKT3 or AKT1 gene as the aetiology of focal somatic mosaicism in the periventricular neuroepithelium. HME may be isolated or associated with neurocutaneous syndromes, particularly epidermal naevus syndromes, also due to somatic mutations. Other tauopathies of early life include: (2) tuberous sclerosis complex; (3) focal cortical dysplasia type 2b (FCD2b); and (4) ganglioglioma, a tumor with dysplastic neurons and neoplastic glial cells. Pathological tau in these infantile cases alters cellular growth and architecture, synaptic function and tissue organization, but does not cause neuronal loss. All infantile tauopathies are defined neuropathologically as a tetrad of (1) dysmorphic and megalocytic neurons; (2) activation of the mTOR signaling pathway; (3) post-zygotic somatic mosaicism; and (4) upregulation of phosphorylated tau. HME and FCD2b may be the same disorder with different timing of the somatic mutation in the mitotic cycles of the neuroepithelium. HME and FCD2b may be the same disorder with different timing of the somatic mutation in the mitotic cycles of the neuroepithelium. Tauopathies must be considered in infantile neurological disease and no longer restricted to adult dementias. The mTOR inhibitor everolimus, already demonstrated to be effective in TSC, also may be a potential treatment in other infantile tauopathies.

Establishment of Tsc2‑deficient rat embryonic stem cells

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by TSC1 or TSC2 mutations. TSC causes the development of tumors in various organs such as the brain, skin, kidney, lung, and heart. The protein complex TSC1/2 has been reported to have an inhibitory function on mammalian target of rapamycin complex 1 (mTORC1). Treatment with mammalian target of rapamycin (mTOR) inhibitors has demonstrated tumor‑reducing effects in patients with TSC but is also associated with various adverse effects. In recent years, experiments involving in vivo differentiation of pluripotent stem cells have been reported as useful in elucidating mechanisms of pathogenesis and discovering new therapeutic targets for several diseases. To reveal the molecular basis of the pathogenesis caused by the Tsc2 mutation, we derived embryonic stem cells (ESCs) from Eker rats, which have the Tsc2 mutation and develop brain lesions and renal tumors. Although several studies have reported the necessity of Tsc1 and Tsc2 regulation to maintain ESCs and hematopoietic stem cells, we successfully established not only Tsc2+/+ and Tsc2+/- ESCs but also Tsc2-/- ESCs. We confirmed that these cells express pluripotency markers and retain the ability to differentiate into all three germ layers. Comprehensive gene expression analysis of Tsc2+/+ and Tsc2+/- ESCs revealed similar profiles, whereas the profile of Tsc2-/- ESCs was distinct from these two. In vitro differentiation experiments using these ESCs combined with in vivo experiments may reveal the mechanism of the tissue‑specific pathogenesis caused by the Tsc2 mutation and identify specific new therapeutic targets.

Targeted Next Generation Sequencing reveals previously unidentified TSC1 and TSC2 mutations

Background

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by mutations in TSC1 and TSC2. Conventional DNA diagnostic screens identify a TSC1 or TSC2 mutation in 75 - 90% of individuals categorised with definite TSC. The remaining individuals either have a mutation that is undetectable using conventional methods, or possibly a mutation in another as yet unidentified gene.

Methods

Here we apply a targeted Next Generation Sequencing (NGS) approach to screen the complete TSC1 and TSC2 genomic loci in 7 individuals fulfilling the clinical diagnostic criteria for definite TSC in whom no TSC1 or TSC2 mutations were identified using conventional screening methods.

Results

We identified and confirmed pathogenic mutations in 3 individuals. In the remaining individuals we identified variants of uncertain clinical significance. The identified variants included mosaic changes, changes located deep in intronic sequences and changes affecting promoter regions that would not have been identified using exon-only based analyses.

Conclusions

Targeted NGS of the TSC1 and TSC2 loci is a suitable method to increase the yield of mutations identified in the TSC patient population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0155-4) contains supplementary material, which is available to authorized users.

Absence of subependymal nodules in patients with tubers suggests possible neuroectodermal mosaicism in tuberous sclerosis complex

AIM

Patients with tuberous sclerosis complex (TSC) with brain involvement usually have both tubers and subependymal nodules (SENs) and the occurrence of one lesion without the other seems to be rare. The aim of this study was to assess the specific clinical manifestations and genotype of patients with one type of lesion or the other but not both.

METHOD

The magnetic resonance images of 220 patients with TSC were reviewed, and patients with either tubers or SENs, but not both, were identified.

RESULTS

Out of a total of 220 patients (95 males, 125 females; mean age 22y 9mo, range 9mo-81y), six (3%) had tubers without SENs (two males; four females; mean age 34y 10mo, range 11-48y); however, no patients with SENs and without tubers were identified. No mutation was identified (NMI) in any of the six patients who underwent mutational analysis of TSC1 and TSC2. Five of the six patients had three or fewer tubers.

INTERPRETATION

We found no patients with SENs but without tubers among our cohort. In all patients with tubers but without SENs, mutational studies of TSC1/TSC2 were negative, and the majority of these had three or fewer tubers. A possible mechanism for patients with NMI and an absence of SENs is a mosaicism with a first postzygotic mutation in the neuroectoderm.

Cortical Tubers: Windows into Dysregulation of Epilepsy Risk and Synaptic Signaling Genes by MicroRNAs

Tuberous sclerosis complex (TSC) is a multisystem genetic disorder caused by mutations in the TSC1 and TSC2 genes. Over 80% of TSC patients are affected by epilepsy, but the molecular events contributing to seizures in TSC are not well understood. Recent reports have demonstrated that the brain is enriched with microRNA activity, and they are critical in neural development and function. However, little is known about the role of microRNAs in TSC. Here, we report the characterization of aberrant microRNA activity in cortical tubers resected from 5 TSC patients surgically treated for medically intractable epilepsy. By comparing epileptogenic tubers with adjacent nontuber tissue, we identified a set of 4 coordinately overexpressed microRNAs (miRs 23a, 34a, 34b*, 532-5p). We used quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomic profiling to investigate the combined effect of the 4 microRNAs on target proteins. The proportion of repressed proteins among the predicted targets was significantly greater than in the overall proteome and was highly enriched for proteins involved in synaptic signal transmission. Among the combinatorial targets were TSC1, coding for the protein hamartin, and several epilepsy risk genes. We found decreased levels of hamartin in epileptogenic tubers and confirmed targeting of the TSC1 3' UTR by miRs-23a and 34a.

The neural crest lineage as a driver of disease heterogeneity in Tuberous Sclerosis Complex and Lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM) is a rare neoplastic disease, best characterized by the formation of proliferative nodules that express smooth muscle and melanocytic antigens within the lung parenchyma, leading to progressive destruction of lung tissue and function. The pathological basis of LAM is associated with Tuberous Sclerosis Complex (TSC), a multi-system disorder marked by low-grade tumors in the brain, kidneys, heart, eyes, lung and skin, arising from inherited or spontaneous germ-line mutations in either of the TSC1 or TSC2 genes. LAM can develop either in a patient with TSC (TSC-LAM) or spontaneously (S-LAM), and it is clear that the majority of LAM lesions of both forms are characterized by an inactivating mutation in either TSC1 or TSC2, as in TSC. Despite this genetic commonality, there is considerable heterogeneity in the tumor spectrum of TSC and LAM patients, the basis for which is currently unknown. There is extensive clinical evidence to suggest that the cell of origin for LAM, as well as many of the TSC-associated tumors, is a neural crest cell, a highly migratory cell type with extensive multi-lineage potential. Here we explore the hypothesis that the types of tumors that develop and the tissues that are affected in TSC and LAM are dictated by the developmental timing of TSC gene mutations, which determines the identities of the affected cell types and the size of downstream populations that acquire a mutation. We further discuss the evidence to support a neural crest origin for LAM and TSC tumors, and propose approaches for generating humanized models of TSC and LAM that will allow cell of origin theories to be experimentally tested. Identifying the cell of origin and developing appropriate humanized models is necessary to truly understand LAM and TSC pathology and to establish effective and long-lasting therapeutic approaches for these patients.

Subependymal giant cell astrocytoma: current concepts, management, and future directions

BACKGROUND

Subependymal giant cell astrocytoma (SEGA) is the most common central nervous system tumor in patients with tuberous sclerosis complex (TSC). SEGAs are generally benign, non-infiltrative lesions, but they can lead to intracranial hypertension, obstructive hydrocephalus, focal neurologic deficits, and even sudden death.

DISCUSSION

Surgical resection has been the standard treatment for SEGAs, and it is generally curative with complete resection. However, not all SEGAs are amenable to safe and complete resection. Gamma Knife stereotactic radiosurgery provides another treatment option as a primary or adjuvant treatment for SEGAs, but it has highly variable response effects with sporadic cases demonstrating its efficacy. Recently, biologically targeted pharmacotherapy with mammalian target of rapamycin (mTOR) inhibitors such as sirolimus and everolimus has provided a safe and efficacious treatment option for patients with SEGAs. However, SEGAs can recur few months after drug discontinuation, indicating that mTOR inhibitors may need to be continued to avoid recurrence. Further studies are needed to evaluate the advantages and adverse effects of long-term treatment with mTOR inhibitors. This review presents an overview of the current knowledge and particularly highlights the surgical and medical options of SEGAs in patients with TSC.

Monoallelic germline TSC1 mutations are permissive for T lymphocyte development and homeostasis in tuberous sclerosis complex individuals

Germline and somatic biallelic mutations of the Tuberous sclerosis complex (TSC) 1 and TSC2 gene products cause TSC, an autosomal dominant multifocal hamartomatosis with variable neurological manifestations. The consequences of TSC1 or TSC2 loss in cells of hematopoietic origin have recently started to be unveiled in mice and showed to hinder the development of proper T cell immunity. To date, the consequences of germline TSC1 mutations and/or its loss in mature human T cells remain to be determined. To address these issues, we analyzed subset representation, phenotype and responsiveness to mitogens in T cells from patients with inherited monoallelic TSC1 mutations, and induced shRNA-mediated TSC1 down-regulation in primary and transformed human T cells. We report that, the distribution of peripheral CD4 and CD8 T cell subsets, their cytokine-secretion profile, and responsiveness to in vitro stimulation were largely preserved in TSC subjects with monoallelic TSC1 germline mutations when compared to healthy controls. Sufficient levels of hamartin and tuberin and proper control of mTOR-dependent signaling in primary T cells from TSC subjects best explained this. In contrast, shRNA-induced down-regulation of TSC1, likely mimicking biallelic inactivation of TSC1, compromised hamartin and tuberin expression and mTORC2/AKT/FoxO1/3 signaling causing both primary and transformed T cells to die by apoptosis. Thus, our results indicate that, while one functional TSC1 allele preserves human T lymphocytes development and homeostasis, TSC1 acute down-regulation is detrimental to the survival of both primary and transformed T cells.

TSC2 epigenetic defect in primary LAM cells. Evidence of an anchorage-independent survival

Tuberous sclerosis complex (TSC) is caused by mutations in TSC1 or TSC2 genes. Lymphangioleiomyomatosis (LAM) can be sporadic or associated with TSC and is characterized by widespread pulmonary proliferation of abnormal α-smooth muscle (ASM)-like cells. We investigated the features of ASM cells isolated from chylous thorax of a patient affected by LAM associated with TSC, named LAM/TSC cells, bearing a germline TSC2 mutation and an epigenetic defect causing the absence of tuberin. Proliferation of LAM/TSC cells is epidermal growth factor (EGF)-dependent and blockade of EGF receptor causes cell death as we previously showed in cells lacking tuberin. LAM/TSC cells spontaneously detach probably for the inactivation of the focal adhesion kinase (FAK)/Akt/mTOR pathway and display the ability to survive independently from adhesion. Non-adherent LAM/TSC cells show an extremely low proliferation rate consistent with tumour stem-cell characteristics. Moreover, LAM/TSC cells bear characteristics of stemness and secrete high amount of interleukin (IL)-6 and IL-8. Anti-EGF receptor antibodies and rapamycin affect proliferation and viability of non-adherent cells. In conclusion, the understanding of LAM/TSC cell features is important in the assessment of cell invasiveness in LAM and TSC and should provide a useful model to test therapeutic approaches aimed at controlling their migratory ability.

Brain somatic mutations: the dark matter of psychiatric genetics?

Although inherited DNA sequences have a well-demonstrated role in psychiatric disease risk, for even the most heritable mental disorders, monozygotic twins are discordant at a significant rate. The genetic variation associated with mental disorders has heretofore been based on the search for rare or common variation in blood cells. This search is based on the premise that every somatic cell shares an identical DNA sequence, so that variation found in lymphocytes should reflect variation present in brain cells. Evidence from the study of cancer cells, stem cells and now neurons demonstrate that this premise is false. Somatic mutation is common in human cells and has been implicated in a range of diseases beyond cancer. The exuberant proliferation of cortical precursors during fetal development provides a likely environment for somatic mutation in neuronal and glial lineages. Studies of rare neurodevelopmental disorders, such as hemimegencephaly, demonstrate somatic mutations in affected cortical cells that cannot be detected in unaffected parts of the brain or in peripheral cells. This perspective argues for the need to investigate somatic variation in the brain as an explanation of the discordance in monozygotic twins, a proximate cause of mental disorders in individuals with inherited risk, and a potential guide to novel treatment targets.

The diverse genetic landscape of neurodevelopmental disorders

Advances in genetic tools and sequencing technology in the past few years have vastly expanded our understanding of the genetics of neurodevelopmental disorders. Recent high-throughput sequencing analyses of structural brain malformations, cognitive and neuropsychiatric disorders, and localized cortical dysplasias have uncovered a diverse genetic landscape beyond classic Mendelian patterns of inheritance. The underlying genetic causes of neurodevelopmental disorders implicate numerous cell biological pathways critical for normal brain development.