Molecular genetic and phenotypic analysis reveals differences between TSC1 and TSC2 associated familial and sporadic tuberous sclerosis

α-[11C]-Methyl-L-tryptophan--PET in 191 patients with tuberous sclerosis complex

OBJECTIVES

This was an observational study done on a large cohort of patients with tuberous sclerosis complex (TSC) to determine whether i) the presence of α-[(11)C]-methyl-l-tryptophan (AMT) hotspots is related to the duration of seizure intractability, ii) the presence of AMT hotspots is related to specific TSC gene mutations, and iii) there is concordance between areas with an AMT hotspot and seizure lateralization/localization on scalp EEG.

METHODS

One hundred ninety-one patients (mean age: 6.7 years; median: 5 years; range: 3 months to 37 years) with TSC and intractable epilepsy were included. All patients underwent AMT-PET scan. AMT uptake in each tuber and normal-appearing cortex was measured and correlated with clinical, scalp EEG, and, if available, electrocorticographic data.

RESULTS

The longer the duration of seizure intractability, the greater the number of AMT hotspots (r = 0.2; p = 0.03). AMT hotspots were seen in both TSC1 and TSC2. There was excellent agreement in seizure focus lateralization between ictal scalp EEG and AMT-PET (Cohen κ 0.94) in 68 of 95 patients in whom both ictal video-EEG and AMT-PET showed lateralizing findings; in 28 of 68 patients (41%), AMT was more localizing. Furthermore, AMT-PET was localizing in 10 of 17 patients (58%) with nonlateralized ictal EEG.

CONCLUSION

AMT-PET, when used together with video-EEG, provides additional lateralization/localization data, regardless of TSC mutation. The duration of seizure intractability may predict the multiplicity of areas with AMT hotspots.

Frequency of TSC1 and TSC2 mutations in American, British, Polish and Taiwanese populations

Tuberous sclerosis (TS) is caused by mutation of the tumor suppressor genes, tuberous sclerosis complex 1 (TSC1) or 2 (TSC2). The aim of the present study was to compare the frequency and types of TSC1 and TSC2 mutations in American, British, Polish and Taiwanese populations. A meta‑analysis of 380 TS patients was performed. Significant differences were analyzed using the Chi-square test and one-way ANOVA analysis. Results showed a difference in frequency for the four populations analyzed. The frequency of TSC1 mutations was twice as high in the American and British populations. However, there were no significant differences in the types of mutations, with insertions of >1 nucleotide being the least frequent. Additionally, in an analysis of the complexity of nucleotide sequences it was demonstrated that the level of sequence complexity in the Polish population was significant higher compared to the remaining populations. Concerning strand bias, in the case of two types of substitutions, C>G/G>C and C>T/G>A, the ratio of corresponding mutations on the two DNA strands was approximately 3:1 and 2:1. In the present study, an increased frequency of C>G/G>C and C>T/G>A mutations in the coding strand was found in the analyzed populations. However, additional studies and larger patient cohorts are required to verify these results.

Novel TSC1 mutation associated with variable phenotypes in tuberous sclerosis

Tuberous sclerosis is an autosomal dominant disorder, caused by mutations of the TSC1 or TSC2 genes resulting in tumor predisposition. Clinical signs include non-malignant brain tumors, skin, eye, heart and kidney abnormalities. The authors report a Hungarian family with broad phenotypic variability. First, the 5-year-old boy, showing the most symptoms was examined, whose first seizure occurred at 15 months and a cranial magnetic resonance imaging revealed numerous intracerebral calcareous foci. Except of hypopigmented skin spots, no other abnormality was found on physical examination. The mother was completely asymptomatic. Epilepsy of the maternal uncle started at the age of 3 years, of his sister at the age of 17 years and of the maternal grandmother at the age of 39 years. At the age of 52 years the grandmother developed renal cysts. Molecular genetic analysis of the family confirmed a de novo heterozygous point mutation (c.2523 C\>T) in exon 20 of the TSC1 gene. The mutation was detected in all examined family members. Despite increasing data on the pathomechanism of tuberous sclerosis, there is still little known about the genetic modifying factors influencing the broad intra- and interfamilial phenotypic variability. Orv. Hetil., 2013, 154, 914–918.

Conditional and domain-specific inactivation of the Tsc2 gene in neural progenitor cells

Tuberous sclerosis complex (TSC) is a genetic disease characterized by multiorgan benign tumors as well as neurological manifestations. Epilepsy and autism are two of the more prevalent neurological complications and are usually severe. TSC is caused by mutations in either the TSC1 (encodes hamartin) or the TSC2 (encodes tuberin) genes with TSC2 mutations being associated with worse outcomes. Tuberin contains a highly conserved GTPase-activating protein (GAP) domain that indirectly inhibits mammalian target of rapamycin complex 1 (mTORC1). mTORC1 dysregulation is currently thought to cause much of the pathogenesis in TSC but mTORC1-independent mechanisms may also contribute. We generated a novel conditional allele of Tsc2 by flanking exons 36 and 37 with loxP sites. Mice homozygous for this knock-in Tsc2 allele are viable and fertile with normal appearing growth and development. Exposure to Cre recombinase then creates an in-frame deletion involving critical residues of the GAP domain. Homozygous conditional mutant mice generated using Emx1(Cre) have increased cortical mTORC1 signaling, severe developmental brain anomalies, seizures, and die within 3 weeks. We found that the normal levels of the mutant Tsc2 mRNA, though GAP-deficient tuberin protein, appear unstable and rapidly degraded. This novel animal model will allow further study of tuberin function including the requirement of the GAP domain for protein stability.

Evolving neurobiology of tuberous sclerosis complex

Over the past decade, there have been numerous advances in our understanding of the molecular pathogenesis of tuberous sclerosis complex (TSC). Following the identification of the TSC1 and TSC2 genes, a link to regulatory control of the mammalian target of rapamycin (mTOR) signaling pathway has paved the way for new therapeutic interventions, and now even approved therapies for TSC. Gene identification has permitted establishment of cell lines and conditional knockout mouse strains to assay how abnormalities in brain structure lead to enhanced excitability, seizures, cognitive disabilities, and other neuropsychological disorders in TSC. Furthermore, work in in vitro systems and analysis of rodent models and human tissue has allowed investigators to study how brain lesions form in TSC. Evolving questions over the next decade include understanding the high clinical variability of TSC, defining why there is a lack of clear genotype-phenotype correlations, and identifying biomarkers for prognosis and stratification. The study of TSC has in many ways reflected a paradigm "bench-to-bedside" success story that serves as a model of many other neurological disorders.

TSC1 controls distribution of actin fibers through its effect on function of Rho family of small GTPases and regulates cell migration and polarity

The tumor-suppressor genes TSC1 and TSC2 are mutated in tuberous sclerosis, an autosomal dominant multisystem disorder. The gene products of TSC1 and TSC2 form a protein complex that inhibits the signaling of the mammalian target of rapamycin complex1 (mTORC1) pathway. mTORC1 is a crucial molecule in the regulation of cell growth, proliferation and survival. When the TSC1/TSC2 complex is not functional, uncontrolled mTORC1 activity accelerates the cell cycle and triggers tumorigenesis. Recent studies have suggested that TSC1 and TSC2 also regulate the activities of Rac1 and Rho, members of the Rho family of small GTPases, and thereby influence the ensuing actin cytoskeletal organization at focal adhesions. However, how TSC1 contributes to the establishment of cell polarity is not well understood. Here, the relationship between TSC1 and the formation of the actin cytoskeleton was analyzed in stable TSC1-expressing cell lines originally established from a Tsc1-deficient mouse renal tumor cell line. Our analyses showed that cell proliferation and migration were suppressed when TSC1 was expressed. Rac1 activity in these cells was also decreased as was formation of lamellipodia and filopodia. Furthermore, the number of basal actin stress fibers was reduced; by contrast, apical actin fibers, originating at the level of the tight junction formed a network in TSC1-expressing cells. Treatment with Rho-kinase (ROCK) inhibitor diminished the number of apical actin fibers, but rapamycin had no effect. Thus, the actin fibers were regulated by the Rho-ROCK pathway independently of mTOR. In addition, apical actin fibers appeared in TSC1-deficient cells after inhibition of Rac1 activity. These results suggest that TSC1 regulates cell polarity-associated formation of actin fibers through the spatial regulation of Rho family of small GTPases.

Initial presentation with dilated cardiomyopathy in a patient of tuberous sclerosis: a rare case report

A 35-year-old man presented with dilated cardiomyopathy, an unusual association with tuberous sclerosis. Clinical history and examination were consistent with tuberous sclerosis including major features of tuberous sclerosis complex (TSC) like facial angiofibroma, shagreen patch, subependymal nodules, and angiomyolipoma of kidney. The clinical manifestations, pathogenesis and evaluation of tuberous sclerosis are discussed.

Tuberous sclerosis complex: genotype/phenotype correlation of retinal findings

OBJECTIVE

To evaluate genotype/phenotype correlations in individuals with astrocytic hamartoma (AH) and retinal achromic patch (AP) in the setting of tuberous sclerosis complex (TSC).

DESIGN

Retrospective consecutive case series.

PARTICIPANTS

A total of 132 patients enrolled in the Cleveland Clinic Foundation Tuberous Sclerosis Program (CCF-TSCP) and 907 patients from the Tuberous Sclerosis Alliance (TSC-A).

METHODS

Patient gender, age at TSC diagnosis, presence of TSC1 or TSC2 mutations, detailed ophthalmic examination findings, systemic manifestations, and whether or not the patient had a diagnosis of epilepsy or cognitive impairment were analyzed.

MAIN OUTCOME MEASURES

Genotype/phenotype correlation of retinal findings and systemic disease manifestations.

RESULTS

No significant difference was found in the prevalence of AH or AP in the CCF-TSCP (36.1%) and TSC-A (34.1%) groups (P = 0.743). Astrocytic hamartomas were bilateral in 43.3% and 18.1% (P=0.009) and multiple in 40.0% and 15.3% (P = 0.008) in the CCF-TSCP and TSC-A groups, respectively. In the CCF-TSCP group, the average number of AH was 4 (range, 2-7). Average tumor size was 1.0 disc diameter (range, 0.5-2.5 disc diameters). The most common location was along the arcades (41.5%), adjacent to the optic nerve (29.2%), and in the retinal periphery (27.7%). In the CCF-TSCP group, AP was observed in 12.0% of patients (40.0% bilateral, 50.0% multiple). The presence of retinal features was associated with giant cell astrocytoma (37.1% vs. 14.6%; P = 0.018), renal angiomyolipoma (60.0% vs. 27.1%; P = 0.003), cognitive impairment (77.1% vs. 43.8%; P = 0.002), and epilepsy (91.4% vs. 70.8% (P = 0.022) in those with and without retinal findings, respectively. In patients with retinal findings in both the CCF-TSCP and TSC-A groups, mutations in TSC2 were more frequent than in TSC1, 3.3 times and 5.8 times, respectively; in those without retinal findings, the relative rates were 0.67 times and 2.3 times, respectively.

CONCLUSIONS

Individuals with retinal findings are more likely to have concomitant subependymal giant cell astrocytomas, renal angiomyolipomas, cognitive impairment, and epilepsy. TSC2 mutations are more frequent in patients with retinal findings than in those without retinal findings.

Evaluation of copy number variations reveals novel candidate genes in autism spectrum disorder-associated pathways

Autism spectrum disorders (ASDs) are highly heritable, yet relatively few associated genetic loci have been replicated. Copy number variations (CNVs) have been implicated in autism; however, the majority of loci contribute to <1% of the disease population. Therefore, independent studies are important to refine associated CNV regions and discover novel susceptibility genes. In this study, a genome-wide SNP array was utilized for CNV detection by two distinct algorithms in a European ancestry case-control data set. We identify a significantly higher burden in the number and size of deletions, and disrupting more genes in ASD cases. Moreover, 18 deletions larger than 1 Mb were detected exclusively in cases, implicating novel regions at 2q22.1, 3p26.3, 4q12 and 14q23. Case-specific CNVs provided further evidence for pathways previously implicated in ASDs, revealing new candidate genes within the GABAergic signaling and neural development pathways. These include DBI, an allosteric binder of GABA receptors, GABARAPL1, the GABA receptor-associated protein, and SLC6A11, a postsynaptic GABA transporter. We also identified CNVs in COBL, deletions of which cause defects in neuronal cytoskeleton morphogenesis in model vertebrates, and DNER, a neuron-specific Notch ligand required for cerebellar development. Moreover, we found evidence of genetic overlap between ASDs and other neurodevelopmental and neuropsychiatric diseases. These genes include glutamate receptors (GRID1, GRIK2 and GRIK4), synaptic regulators (NRXN3, SLC6A8 and SYN3), transcription factor (ZNF804A) and RNA-binding protein FMR1. Taken together, these CNVs may be a few of the missing pieces of ASD heritability and lead to discovering novel etiological mechanisms.

Microdeletion and microduplication syndromes

During the past decade, widespread use of microarray-based technologies, including oligonucleotide array comparative genomic hybridization (aCGH) and single nucleotide polymorphism (SNP) genotyping arrays have dramatically changed our perspective on genome-wide structural variation. Submicroscopic genomic rearrangements or copy-number variation (CNV) have proven to be an important factor responsible for primate evolution, phenotypic differences between individuals and populations, and susceptibility to many diseases. The number of diseases caused by chromosomal microdeletions and microduplications, also referred to as genomic disorders, has been increasing at a rapid pace. Microdeletions and microduplications are found in patients with a wide variety of phenotypes, including Mendelian diseases as well as common complex traits, such as developmental delay/intellectual disability, autism, schizophrenia, obesity, and epilepsy. This chapter provides an overview of common microdeletion and microduplication syndromes and their clinical phenotypes, and discusses the genomic structures and molecular mechanisms of formation. In addition, an explanation for how these genomic rearrangements convey abnormal phenotypes is provided.

Metabotropic glutamate receptor-dependent long-term depression is impaired due to elevated ERK signaling in the ΔRG mouse model of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) and fragile X syndrome (FXS) are caused by mutations in negative regulators of translation. FXS model mice exhibit enhanced metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD). Therefore, we hypothesized that a mouse model of TSC, ΔRG transgenic mice, also would exhibit enhanced mGluR-LTD. We measured the impact of TSC2-GAP mutations on the mTORC1 and ERK signaling pathways and protein synthesis-dependent hippocampal synaptic plasticity in ΔRG transgenic mice. These mice express a dominant/negative TSC2 that binds to TSC1, but has a deletion and substitution mutation in its GAP-domain, resulting in inactivation of the complex. Consistent with previous studies of several other lines of TSC model mice, we observed elevated S6 phosphorylation in the brains of ΔRG mice, suggesting upregulated translation. Surprisingly, mGluR-LTD was not enhanced, but rather was impaired in the ΔRG transgenic mice, indicating that TSC and FXS have divergent synaptic plasticity phenotypes. Similar to patients with TSC, the ΔRG transgenic mice exhibit elevated ERK signaling. Moreover, the mGluR-LTD impairment displayed by the ΔRG transgenic mice was rescued with the MEK-ERK inhibitor U0126. Our results suggest that the mGluR-LTD impairment observed in ΔRG mice involves aberrant TSC1/2-ERK signaling.

An Australian tuberous sclerosis cohort: are surveillance guidelines being met?

AIM

This study aims to describe the phenotypic and genotypic characteristics of 45 Australian patients with tuberous sclerosis complex (TSC), to assess risk factors for intellectual disability, to compare patients with TSC1 and TSC2 mutations and to assess adherence to surveillance recommendations.

METHODS

Phenotypic features were recorded in 45 patients who fulfilled established criteria for a diagnosis of definite TSC. All patients underwent TSC1 and TSC2 sequencing and multiplex ligand probe amplification. Features were compared in patients with TSC1 mutations versus TSC2 mutations. Recent surveillance was recorded at the point of first contact. Surveillance adherence was compared in the adult and paediatric cohorts.

RESULTS

This cohort consisted of 31 children and 14 adults with definite TSC. The rates of TSC manifestations and TSC1 and TSC2 mutation detection rates were consistent with previous studies. There was a trend towards greater severity for patients with TSC2 mutations compared with their TSC1 counterparts, particularly for autistic spectrum disorder, but this did not reach statistical significance. The presence of seizures was shown to be a risk factor for intellectual disability (P < 0.001). Overall, 12/45 patients (27%) were not undergoing recommended surveillance at the point of first contact. Surveillance guidelines were being followed in 3/31 (11%) children compared with 9/14 (64%) adult patients (P < 0.05).

CONCLUSIONS

The genotypic and phenotypic characteristics of this TSC cohort were consistent with previous studies. Surveillance rates in adult patients were significantly lower than in paediatric patients. This highlights the need for patients with TSC to undergo a focussed transition into adult services.

Impaired social interactions and motor learning skills in tuberous sclerosis complex model mice expressing a dominant/negative form of tuberin

Tuberous sclerosis complex (TSC) is a genetic disorder characterized by the development of hamartomas in multiple organs. Neurological manifestation includes cortical dysplasia, epilepsy, and cognitive deficits such as mental impairment and autism. We measured the impact of TSC2-GAP mutations on cognitive processes and behavior in, ΔRG transgenic mice that express a dominant/negative TSC2 that binds to TSC1, but has mutations affecting its GAP domain and its rabaptin-5 binding motif, resulting in inactivation of the TSC1/2 complex. We performed a behavioral characterization of the ΔRG transgenic mice and found that they display mild, but significant impairments in social behavior and rotarod motor learning. These findings suggest that the ΔRG transgenic mice recapitulate some behavioral abnormalities observed in human TSC patients.

Genetics and molecular biology of tuberous sclerosis complex

Tuberous Sclerosis Complex is a multisystem disorder exhibiting a wide range of manifestations characterized by tumour-like lesions called hamartomas in the brain, skin, eyes, heart, lungs and kidneys. Tuberous Sclerosis Complex is genetically determined with an autosomal dominant inheritance and is caused by inactivating mutations in either the TSC1 or TSC2 genes. TSC1/2 genes play a fundamental role in the regulation of phosphoinositide 3-kinase (PI3K) signalling pathway, inhibiting the mammalian target of rapamycin (mTOR) through activation of the GTPase activity of Rheb. Mutations in TSC1/2 genes impair the inhibitory function of the hamartin/tuberin complex, leading to phosphorylation of the downstream effectors of mTOR, p70 S6 kinase (S6K), ribosomal protein S6 and the elongation factor binding protein 4E-BP1, resulting in uncontrolled cell growth and tumourigenesis.

Despite recent promising genetic, diagnostic, and therapeutic advances in Tuberous Sclerosis Complex, continuing research in all aspects of this complex disease will be pivotal to decrease its associated morbidity and mortality. In this review we will discuss and analyse all the important findings in the molecular pathogenesis of Tuberous Sclerosis Complex, focusing on genetics and the molecular mechanisms that define this multisystemic disorder.

Genetic analysis of tuberous-sclerosis genes 1 and 2 in nonlesional focal epilepsy

Germline mutations of TSC1 (harmartin) and TSC2 (tuberin) are known to cause tuberous sclerosis (TSC), an autosomal dominant disorder with severe neurological and systemic manifestations. In addition, increasing data indicate aberrant patterns of allelic variants in patients with lesion-associated epilepsy, but absence of other stigmata of TSC. Animal models of TSC suggested that mutations in the TSC2 gene, even in absence of manifest neuropathological changes, induce aberrant neuronal activity. On this basis, we have carried out a mutational analysis of TSC1 and TSC2 in patients with pharmarcoresistant focal epilepsy without evidence of epileptogenic lesions on neuroradiological and histopathological examination (n=10). SSCP analysis revealed an allelic variant of TSC2 to be significantly increased (exon 41: 50.0% vs controls 14%, P=0.0132), which previously was reported to be increased in gangliogliomas and mineralized focal cortical dysplasia as well. Our data suggest allelic imbalances of TSC2 in nonlesional focal epileptic tissue.

Clinical and molecular insights into tuberous sclerosis complex renal disease

Patients with tuberous sclerosis complex are at great risk of developing renal lesions as part of their disease. These lesions include renal cysts and tumors. Significant advances in understanding the cell biology of these renal lesions has already led to clinical trials demonstrating that pharmacological interventions are likely possible. This review focuses on the pathology of these renal lesions, their underlying cell biology, and the possible therapeutic strategies that may prove to significantly improve care for these patients.

Evidence for population variation in TSC1 and TSC2 gene expression

BACKGROUND

Tuberous sclerosis complex (TSC) is an autosomal dominant neurogenetic disorder caused by mutations in one of two genes, TSC1 or TSC2, which encode the proteins hamartin and tuberin, respectively 123. Common features of TSC include intractable epilepsy, mental retardation, and autistic features. TSC is associated with specific brain lesions, including cortical tubers, subependymal nodules and subependymal giant cell astrocytomas. In addition, this disease frequently produces characteristic tumors, termed hamartomas, in the kidneys, heart, skin, retina, and lungs. Disease severity in TSC can be quite variable and is not determined by the primary mutation alone. In fact, there is often considerable variability in phenotype within single families, where all affected individuals carry the same mutation. Factors suspected to influence phenotype in TSC include the specific primary mutation, random occurrence of second-hit somatic mutations, mosaicism, "modifying genes", and environmental factors. In addition to these factors, we hypothesize that differences in mRNA expression from the non-mutated TSC allele, or possibly from the mutated allele, play a part in modifying disease severity. Common genetic variants that regulate mRNA expression have previously been shown to play important roles in human phenotypic variability, including disease susceptibility. A prediction based on this idea is that common regulatory variants that influence disease severity in TSC should be detectable in non-affected individuals.

METHODS

A PCR/primer extension assay was used to measure allele specific expression of TSC1 and TSC2 mRNAs in leukocytes isolated from normal volunteers. This assay can be used to measure "allelic expression imbalance" (AEI) in individuals by making use of heterozygous "marker" single nucleotide polymorphisms (SNPs) located within their mRNA.

RESULTS

In this study we show for the first time that TSC1 and TSC2 genes exhibit allele-specific differences in mRNA expression in blood leukocytes isolated from normal individuals.

CONCLUSIONS

These results support the possibility that allele-specific variation in TSC mRNA expression contributes to the variable severity of symptoms in TSC patients.

Tsc2 gene inactivation causes a more severe epilepsy phenotype than Tsc1 inactivation in a mouse model of tuberous sclerosis complex

Tuberous Sclerosis Complex (TSC) is an autosomal dominant, multi-system disorder, typically involving severe neurological symptoms, such as epilepsy, cognitive deficits and autism. Two genes, TSC1 and TSC2, encoding the proteins hamartin and tuberin, respectively, have been identified as causing TSC. Although there is a substantial overlap in the clinical phenotype produced by TSC1 and TSC2 mutations, accumulating evidence indicates that TSC2 mutations cause more severe neurological manifestations than TSC1 mutations. In this study, the neurological phenotype of a novel mouse model involving conditional inactivation of the Tsc2 gene in glial-fibrillary acidic protein (GFAP)-positive cells (Tsc2(GFAP1)CKO mice) was characterized and compared with previously generated Tsc1(GFAP1)CKO mice. Similar to Tsc1(GFAP1)CKO mice, Tsc2(GFAP1)CKO mice exhibited epilepsy, premature death, progressive megencephaly, diffuse glial proliferation, dispersion of hippocampal pyramidal cells and decreased astrocyte glutamate transporter expression. However, Tsc2(GFAP1)CKO mice had an earlier onset and higher frequency of seizures, as well as significantly more severe histological abnormalities, compared with Tsc1(GFAP1)CKO mice. The differences between Tsc1(GFAP1)CKO and Tsc2(GFAP1)CKO mice were correlated with higher levels of mammalian target of rapamycin (mTOR) activation in Tsc2(GFAP1)CKO mice and were reversed by the mTOR inhibitor, rapamycin. These findings provide novel evidence in mouse models that Tsc2 mutations intrinsically cause a more severe neurological phenotype than Tsc1 mutations and suggest that the difference in phenotype may be related to the degree to which Tsc1 and Tsc2 inactivation causes abnormal mTOR activation.

Targeted treatments for cognitive and neurodevelopmental disorders in tuberous sclerosis complex

Until recently, the neuropsychiatric phenotype of tuberous sclerosis complex (TSC) was presumed to be caused by the structural brain abnormalities and/or seizures seen in the disorder. However, advances in the molecular biology of the disorder have shown that TSC is a mammalian target of rapamycin (mTOR) overactivation syndrome, and that direct molecular pathways exist between gene mutation and cognitive/neurodevelopmental phenotype. Molecularly-targeted treatments using mTOR inhibitors (such as rapamycin) are showing great promise for the physical and neurological phenotype of TSC. Pre-clinical and early-phase clinical studies of the cognitive and neurodevelopmental features of TSC suggest that some of the neuropsychiatric phenotypes might also be reversible, even in adults with the disorder. TSC, fragile X, neurofibromatosis type 1, and disorders associated with phosphatase and tensin homo (PTEN) mutations, all signal through the mTOR signaling pathway, with the TSC1-TSC2 protein complex as a molecular switchboard at its center. Together, these disorders represent as much as 14% of autism spectrum disorders (ASD). Therefore, we suggest that this signaling pathway is a key to the underlying pathophysiology of a significant subset of individuals with ASD. The study of molecularly targeted treatments in TSC and related disorders, therefore, may be of scientific and clinical value not only to those with TSC, but to a larger population that may have a neuropsychiatric phenotype attributable to mTOR overactivation or dysregulation.

Management of subependymal giant cell tumors in tuberous sclerosis complex: the neurosurgeon's perspective

BACKGROUND

Tuberous sclerosis complex (TSC), an autosomal dominant genetic disorder, can lead to the development of hamartomas in various organs, including the heart, lungs, kidneys, skin and brain. The management of subependymal giant cell tumors (SGCTs) is still controversial, and peri- and/or intraventricular neoplasms may lead to life-threatening hydrocephalus. In the last years, many progresses have been made in research into the tumorigenesis and behaviors of SGCTs. This review aims to clarify the specific role of neurosurgeons in the multidisciplinary management of SGCTs in children with TSC.

DATA SOURCES

Based on the recent scientific literature and personal experience, we reviewed the up-to-date data and discussed the trends in the management of SGCTs in children with TSC. The data were collected after a bibliography made using PubMed/Medline with these terms: subependymal, subependymal giant cell astrocytoma, subependymal giant cell tumor, and tuberous sclerosis complex.

RESULTS

SGCTs are shown to be generated from a glioneuronal lineage, but their filiation with subependymal nodules (SENs) is still under debate. While SENs may develop anywhere in the ventricular walls, SGCTs arise almost exclusively around the Monro foramina. In children with TSC, precise clinical and/or imaging criteria are mandatory to differentiate SENs that are always asymptomatic and riskless from SGCTs that have the potential to grow and therefore to obstruct cerebrospinal fluid pathways leading to hydrocephalus.

CONCLUSIONS

An earlier diagnosis of SGCT in neurologically asymptomatic children with TSC may allow a precocious surgical removal of the tumor before the installation of increased intracranial pressure signs, an attitude that is being progressively adopted to lessen the morbimortality rate.

The tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that results from mutations in the TSC1 or TSC2 genes and is associated with hamartoma formation in multiple organ systems. The neurological manifestations of TSC are particularly challenging and include infantile spasms, intractable epilepsy, cognitive disabilities, and autism. Progress over the past 15 years has demonstrated that the TSC1 or TSC2 encoded proteins modulate cell function via the mTOR signaling cascade and serve as keystones in regulating cell growth and proliferation. The mTOR pathway provides an intersection for an intricate network of protein cascades that respond to cellular nutrition, energy levels, and growth-factor stimulation. In the brain, TSC1 and TSC2 have been implicated in cell body size, dendritic arborization, axonal outgrowth and targeting, neuronal migration, cortical lamination, and spine formation. Antagonism of the mTOR pathway with rapamycin and related compounds may provide new therapeutic options for TSC patients.

Comorbidities in pediatric epilepsy: beyond "just'' treating the seizures

The goal of this review is to discuss the comorbidities reported in specific epilepsy syndromes to examine possible underlying causes or associations and to present data on current therapies for these conditions. Comorbid conditions including cognitive impairment, neuropsychiatric problems, and social difficulties are common in children with epilepsy, and often more disabling than the seizures themselves. Biological factors associated with a greater risk of comorbidity in epilepsy include younger age at seizure onset, cognitive impairment, temporal or frontal lobe onset, and intractability. Social factors correlating with greater risk include lower socioeconomic status, lower parental education level, and poorer family function. These comorbid conditions not only have a significant impact on the child but also are a source of increased stress and burden for families. Increased awareness and early diagnosis of these conditions may affect therapeutic intervention and long-term outcome as well as assist in better understanding of potential risk factors and biological mechanisms.

Increased frequency of distinct TSC2 allelic variants in focal cortical dysplasias with balloon cells and mineralization

Focal cortical dysplasias with balloon cells (FCD(IIb)) usually present with characteristic imaging and molecular features, that is, a transmantle sign on fluid-attenuated inversion recovery MRI and abundance of allelic variants of the tuberous sclerosis gene 1 (TSC1). Recently, we observed several mineralized lesions (n = 5) lacking this MRI pattern and which surprisingly turned out as FCD(IIb) upon neuropathological examination. These mineralized FCD(IIb) revealed an increased frequency of TSC2 allelic variants but not TSC1 (intron 31: 60% vs. 11% in controls; P = 0.0164, exon 41: 40% vs. 6.5% in controls; P = 0.0441). Mineralized FCD(IIb) have a favorable postsurgical outcome and need consideration in the presurgical differential diagnosis of calcified lesions associated with pharmacoresistant focal epilepsies.

Unusual radiological presentation of tuberous sclerosis complex with leptomeningeal angiomatosis associated with a hypomorphic mutation in the TSC2 gene

Tuberous sclerosis complex is an autosomal dominant disorder affecting primarily the central nervous system, skin, and kidney caused by mutations in the TSC1 and TSC2 genes. Diagnosis is established with the identification of various neurocutaneous symptoms and multiple organ system hamartomas. The authors report on a 9-year-old patient with episodes of vertigo and headache followed by full spontaneous recovery. There was no history of seizures, mental retardation, or other neurologic sequelae, and psychomotor development was normal. Magnetic resonance imaging revealed pial angiomatosis of the left cerebellum and calcifications in the left parieto-occipital lobe consistent with the diagnosis of Sturge-Weber syndrome. At the age of 13, multiple renal angiomyolipomas and a single hypomelanotic macule were found, and subsequent imaging revealed several cortical tuberi. The diagnosis was confirmed by sequence analysis, which identified a novel missense mutation p.Ala460Thr in exon 13 of the TSC2 gene. Thus, mild tuberous sclerosis due to a hypomorphic mutation in TSC2 may present with isolated leptomeningeal angiomatosis.

Recent advances in neurobiology of Tuberous Sclerosis Complex

Tuberous Sclerosis Complex (TSC) is a multisystem genetic disorder with variable phenotypic expression, due to a mutation in one of the two genes, TSC1 and TSC2, and a subsequent hyperactivation of the downstream mTOR pathway, resulting in increased cell growth and proliferation. The central nervous system is consistently involved in TSC, with 90% of individuals affected showing structural abnormalities, and almost all having some degree of CNS clinical manifestations, including seizures, cognitive impairment and behavioural problems. TSC is proving to be a particularly informative model for studying contemporary issues in developmental neurosciences. Recent advances in the neurobiology of TSC from molecular biology, molecular genetics, and animal model studies provide a better understanding of the pathogenesis of TSC-related neurological symptoms. Rapamycin normalizes the dysregulated mTOR pathway, and recent clinical trials have demonstrated its efficacy in various TSC manifestations, suggesting the possibility that rapamycin may have benefit in the treatment of TSC brain disease.

Behavior problems in children with tuberous sclerosis complex and parental stress

Behavioral problems are common in children with tuberous sclerosis complex (TSC) and can be challenging to manage at home. Standardized measures were used to assess behavior in 99 pediatric patients with TSC and to evaluate parenting stress in their parents. About 40% of the pediatric patients presented clinically significant behavioral problems, most frequently involving symptoms of autism spectrum disorder, inattention, and hyperactivity. Higher seizure frequency, mixed seizure disorder, and low intellectual functioning placed the patient at significant risk for behavior problems. Almost 50% of participating parents reported experiencing clinically significant parenting stress, which was associated with specific characteristics of the child, including the presence of current seizures, a history of psychiatric diagnosis, low intelligence, and behavioral problems. Clinicians should be aware that behavioral problems are prominent in children with TSC. Referrals for behavioral intervention and monitoring of parental stress should be included in the medical management of children with TSC.

Infantile spasms in tuberous sclerosis complex: prognostic utility of EEG

PURPOSE

To assess cognitive and epilepsy outcomes in tuberous sclerosis complex (TSC) patients with a history of infantile spasms (IS), in relation to spasm history, electroencephalography (EEG) characteristics, genetic mutation, and treatment history.

METHODS

The authors conducted a retrospective review of 45 children and adults with TSC and a history of IS. EEG reports from the time of spasms were evaluated for all patients, and EEG tracings were accessible and evaluated for 20 patients.

RESULTS

Clinical outcome was unfavorable for the majority of patients. However, 33% had experienced at least one year of seizure freedom at follow-up, and 24% of those tested had IQs above 70. Hypsarrhythmia severity scores varied widely, with some EEGs severely hypsarrhythmic and others essentially normal. Lower IQ was significantly associated with higher hypsarrhythmia severity scores on EEG report, the presence of background disorganization on EEG report, the absence of normal sleep patterns on EEG, and a lower degree of treatment success on vigabatrin. A relationship between poor cognitive outcome and poor epilepsy outcome was confirmed. The correlation between poor epilepsy outcome and a greater degree of background disorganization on EEG approached significance, as did the association between subsequent intractable epilepsy and an older age at IS cessation. A greater than expected ratio of TSC2 to TSC1 patients was observed across this IS population.

DISCUSSION

Early detection and successful treatment portend a more favorable outcome in TSC patients with IS. Although EEG findings in these patients vary, specific characteristics may serve as clinically useful prognostic markers.

Bladder tumour-derived somatic TSC1 missense mutations cause loss of function via distinct mechanisms

More than 50% of transitional cell carcinomas of the bladder show loss of heterozygosity of a region spanning the TSC1 locus at 9q34 and mutations of TSC1 have been identified in 14.5% of tumours. These comprise nonsense mutations, splicing mutations, small deletions and missense mutations. Missense mutations are only rarely found in the germline in TSC disease. Therefore, we have examined six somatic missense mutations found in bladder cancer to determine whether these result in loss of function. We describe loss of function via distinct mechanisms. Five mutations caused mutually exclusive defects at mRNA and protein levels. Of these, two mutations caused pre-mRNA splicing errors that were predicted to result in premature protein truncation and three resulted in markedly reduced stability of exogenous TSC1 protein. Primary tumours with aberrant TSC1 pre-mRNA splicing were confirmed as negative for TSC1 expression by immunohistochemistry. Expression was also significantly reduced in a tumour with a TSC1 missense mutation resulting in diminished protein half-life. A single TSC1 missense mutation identified in a tumour with retained heterozygosity of the TSC1 region on chromosome 9 caused an apparently TSC2- and mTOR-independent localization defect of the mutant protein. We conclude that although TSC1 missense mutations do not play a major role in causation of TSC disease, they represent a significant proportion of somatic loss of function mutations in bladder cancer.

Tuberous Sclerosis Complex With Polycystic Kidney Disease of the Adult Type: the TSC2/ADPKD1 Contiguous Gene Syndrome

Although different diseases, tuberous sclerosis complex and autosomal dominant polycystic kidney disease have been seen in association, the molecular basis of this being the proximity of tuberous sclerosis complex 2 and polycystic kidney disease 1 genes on the same chromosome (16p13.3). Therefore, the classic autosomal dominant polycystic kidney disease renal phenotype may occur in the context of tuberous sclerosis complex disease as a result of large deletions involving both the polycystic kidney disease 1 and tuberous sclerosis complex 2 genes. This is known as the tuberous sclerosis complex 2/autosomal dominant polycystic kidney disease 1 contiguous gene syndrome. The criteria for this condition are fulfilled when renal lesions typical for classic autosomal dominant polycystic kidney disease phenotype are associated with tuberous sclerosis complex phenotype. We present a new case of the sporadic form of this genetic disorder. The diagnosis of tuberous sclerosis complex in this patient was established on the presence of major and minor features, and the diagnosis of ADPKD was based on the presence of numerous large roundish renal cysts lined by a nondescript tubular epithelium. Sporadic cases of autosomal dominant polycystic kidney disease and tuberous sclerosis complex do occur. Molecular analysis was not performed because the patient's parents refused permission.

Prenatal diagnosis of cerebral lesions in Tuberous sclerosis complex (TSC). Case report and review of the literature

Tuberous sclerosis complex (TSC) is an autosomal-dominant neurocutaneous disorder with multi-organ involvement. The diagnosis is suspected at fetal ultrasound on the discovery of multiple cardiac rhabdomyomas (CRs). They typically develop in utero and undergo spontaneous regression during the first years of live. With developing neuroradiological methods more light is shed on antenatal cerebral lesions like cortical tubers or giant cell astrocytomas. Unfortunately these do not regress, but instead are in principle progressive in size and number, correlated with epilepsy, mental retardation and behavioral problems. It is unknown whether fetal cerebral lesions, are always correlated with a poor neurological outcome or a progressive course of disease. This makes prenatal counseling extremely difficult. We report one case of de novo TSC with first detection of cortical tubers on fetal ultrasound, later developing multiple CRs. The pregnancy was continued and the child is developing well during 16 months of follow-up. Minor motor seizures from the 10th month onwards are successfully treated with Valproate. The published cases with antenatal diagnosis of TSC are revised, trying to get more insight into the postnatal course of prenatally diagnosed TSC. This is crucial, either when termination of pregnancy (TOP) is considered, but even more for proper postnatal care and follow-up.

The neurobiology of the tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a multisystem disorder that affects numerous organ systems. Brain lesions that form during development, known as tubers, are highly associated with epilepsy, cognitive disability, and autism. Following the identification of two genes and their encoded proteins, TSC1 (hamartin) and TSC2 (tuberin), responsible for TSC, identification of several downstream protein cascades that might be affected in TSC have been discovered. Of primary importance is the mammalian target of rapamycin pathway that controls cell growth and protein synthesis. The mechanisms governing brain lesion growth have not been fully identified but likely altered regulation of the mammalian target of rapamycin cascade by hamartin and tuberin during development leads to aberrant cell growth. Secondary effects of TSC gene mutations might disrupt normal neuronal migration and cerebral cortical lamination. Numerous studies have identified changes in gene and protein expression in animal models of TSC and in human TSC brain specimens that contribute to altered brain cytoarchitecture. This review will provide an overview of the neurobiological aspects of TSC.

Psychiatric comorbid conditions in a clinic population of 241 patients with tuberous sclerosis complex

Psychiatric symptoms were retrospectively assessed in a clinic population of 241 children and adults with tuberous sclerosis complex (TSC). Sixty-six (27%) patients had a history of mood disorder symptoms, 66 (27%) had a history of anxiety disorder symptoms, 73 (30%) had a history of attention-deficit hyperactivity disorder (ADHD) symptoms, and 68 (28%) had a history of aggressive/disruptive behavior disorder symptoms. Significant relationships were found between these symptoms and patient age, gender, genetic mutation, seizure history, surgical history, cognitive impairment, features of autism or pervasive developmental disorder, and neurological manifestations of TSC. In 43 patients seen by at least one of two affiliated psychiatrists, the most common formal diagnoses were anxiety disorders (28%), mood disorders (26%), adjustment disorders (21%), ADHD (21%), and mental disorders not otherwise specified due to general medical condition (42%). Citalopram demonstrated efficacy in treating anxiety and depression, and risperidone, in treating problematic behaviors.

Alterations of phosphatidylinositol 3-kinase pathway components in epilepsy-associated glioneuronal lesions

Low-grade glioneuronal lesions involving tumors such as gangliogliomas and focal cortical dysplasias (FCD) predispose individuals to pharmacoresistant epilepsy. A frequent variant of FCD is composed of dysplastic cytomegalic neurons and Taylor-type balloon cells (FCD(IIb)). Those are similar to cellular elements, which are present in cortical tubers in the autosomal dominant inherited tuberous sclerosis complex (TSC). This phacomatosis is caused by mutations in the TSC1 or TSC2 genes. Recent data have indicated accumulation of distinct allelic variants of TSC1 also in FCD(IIb). TSC1 represents a key factor in the phosphatidylinositol 3-kinase (PI3K) pathway. A variety of alterations in the PI3K-pathway have been recently reported in epilepsy-associated glioneuronal malformations. Here, we discuss pathogenetic similarities and differences between cortical dysplasias as well epilepsy-associated glioneuronal tumors and TSC-associated cortical tubers with a focus on PI3K-pathway components including ezrin, radixin and moesin (ERM), which represent downstream effectors involved in cytoskeleton-membrane interference. No evidence has been found for mutational events of ERM genes to play a major pathogenetic role in epilepsy-associated glioneuronal malformations. In contrast, aberrant expression of ERM proteins in FCDs and gangliogliomas was observed. These alterations may relate to compromised interactions of dysplastic cellular components in epilepsy-associated glioneuronal lesions and be involved in aberrant PI3K-pathway signaling in epilepsy-associated malformations. However, the underlying cause of PI3K-pathway activation and the functional relationship of PI3K-pathway activity to generation of seizures in epilepsy-associated glioneuronal lesions will need to be determined in the future.

Antisense suppression of TSC1 gene product, hamartin, enhances neurite outgrowth in NGF-treated PC12h cells

Tuberous sclerosis complex (TSC) is an autosomal dominant inherited disorder characterized by benign tumors (hamartomas) in various organs. The brain is one of the most severely affected organs with neuropsychiatric disorders including epilepsy, mental retardation and autism. The identification of TSC genes (TSC1 and TSC2) and their gene products (hamartin and tuberin, respectively), revealed that they function together as a complex. However, mutations in TSC2 are often accompanied by more severe neurologic deficits. Here, we show that hamartin and tuberin play different roles in NGF-treated cultured neuronal cells PC12h. The level of hamartin in PC12h cells was slightly and gradually increased, while those of tuberin rapidly increased upon NGF-induced neuronal differentiation in PC12h cells. Antisense for TSC1 (TSC1-AS) or TSC2-AS reduced expression of hamartin or tuberin, respectively, and enhanced S-phase of cell cycle in PC12h cells. Suppression of hamartin significantly enhanced neurite outgrowth after NGF-treatment in PC12h cells, while suppression of tuberin inhibited neurite outgrowth. Expression of activated V14RhoA reverted TSC1-AS induced abnormal neurite development. These results suggest that loss of hamartin results in abnormal neurite elongation through Rho inactivation in NGF-treated PC12h cells, which may be associated with the neurological manifestations of TSC.

The tuberous sclerosis complex proteins – a GRIPP on cognition and neurodevelopment

Tuberous sclerosis complex (TSC) is a multi-system disorder associated with mutations in the TSC1 (hamartin) or TSC2 (tuberin) genes. The neurocognitive features of TSC show wide variability and have generally been attributed to structural brain abnormalities and/or seizures. We review the fundamental roles of TSC1 and TSC2 in cell signalling and propose that because the hamartin-tuberin complex (hereafter referred to as TSC1-2) acts as a global regulator and integrator of a range of physiological processes ('GRIPP') the neurocognitive manifestations of TSC result directly from cell-signalling abnormalities. Under the GRIPP hypothesis, the spectrum of neurodevelopmental abnormalities is caused by the biochemical consequences of individual TSC1 and TSC2 mutations. Recognizing the importance of signalling disruption in the brain might improve our understanding of other neurocognitive disorders.

Abnormal giant cells in the cerebral lesions of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by mutations of either of the two tumor suppressor genes, TSC1 and TSC2, encoding hamartin and tuberin, respectively. TSC is pathologically characterized by the occurrence of multiple hamartias (focal dysplasias) and hamartomas (benign tumors) in the brain and many other organs. Cortical tubers are hamartias in the cerebral cortex responsible for many neuropsychiatric symptoms of TSC. Unlike TSC-associated hamartomas, cortical tubers do not result from second somatic mutations of the TSC gene, and the mechanism by which they occur remains obscure. Histologically, the most conspicuous feature of cortical tubers is the presence of abnormal giant cells, which show abnormal size and differentiation. Recent studies on human TSC and its animal models have elucidated the critical roles of hamartin and tuberin regulating the growth and differentiation of neural cells.

Genotype/phenotype correlation in 325 individuals referred for a diagnosis of tuberous sclerosis complex in the United States

Tuberous sclerosis complex is an autosomal dominant neurocutaneous disorder marked by hamartoma growth in multiple organ systems. We performed mutational analyses on 325 individuals with definite tuberous sclerosis complex diagnostic status. We identified mutations in 72% (199/257) of de novo and 77% (53/68) of familial cases, with 17% of mutations in the TSC1 gene and 50% in the TSC2 gene. There were 4% unclassified variants and 29% with no mutation identified. Genotype/phenotype analyses of all observed tuberous sclerosis complex findings in probands were performed, including several clinical features not analyzed in two previous large studies. We showed that patients with TSC2 mutations have significantly more hypomelanotic macules and learning disability in contrast to those with TSC1 mutations, findings not noted in previous studies. We also observed results consistent with two similar studies suggesting that individuals with mutations in TSC2 have more severe symptoms. On performing meta-analyses of our data and the other two largest studies in the literature, we found significant correlations for several features that individual studies did not have sufficient power to conclude. Male patients showed more frequent neurologic and eye symptoms, renal cysts, and ungual fibromas. Correlating genotypes with phenotypes should facilitate the disease management of tuberous sclerosis complex.

The psychopathologies of children and adolescents with tuberous sclerosis complex (TSC): a postal survey of UK families

Tuberous Sclerosis Complex (TSC) is a multi-system genetic disorder associated with a wide range of physical features and very high rates of numerous neurocognitive manifestations. However, there is great variability of expression of these features and understanding of the mechanisms underlying this variability is still limited. Mental retardation (MR) and male gender are known to be associated with increased risks of psychopathologies in the general population, but no study has examined these subgroups in TSC as possible contributors to the variable expression observed. It has also remained unclear whether familial-sporadic differences may contribute to variable expression. In this postal survey, UK families reported the frequency and range of physical and behavioural abnormalities in 265 children and adolescents with TSC. Analysis revealed no gender or familial-sporadic differences. Children with MR were significantly more likely to have an autism spectrum disorder, attention deficit-related symptoms and speech and language difficulties. They were more likely to have a history of epilepsy, facial angiofibromata and shagreen patches and tended to have a greater number of physical features of the disorder. However, about one third of the children without MR had features suggestive of a developmental disorder. Anxiety symptoms, depressed mood and aggressive outbursts occurred at equally high rates in those with and without MR. These findings show that TSC can place any child or adolescent at significantly increased risk of a range of neurodevelopmental disabilities. These difficulties, often not recognised, require significant clinical and research attention.

Unusually mild tuberous sclerosis phenotype is associated with TSC2 R905Q mutation

OBJECTIVE

To report the clinical manifestations and functional aspects of Tuberous Sclerosis Complex (TSC), resulting from Codon 905 mutations in TSC2 gene.

METHODS

We performed a detailed study of the TSC phenotype and genotype in a large French-Canadian kindred (Family A). Subsequently, clinical and molecular data on 18 additional TSC families with missense mutations at the same codon of TSC2 were collected. Functional studies were performed on the different missense changes and related to the phenotype.

RESULTS

A 2714G>A (R905Q) mutation was identified in Family A. The TSC phenotype in this family was unusually mild and characterized by hypomelanotic macules or focal seizures that remitted spontaneously or were easily controlled with medication. Diagnostic criteria were met in only a minority of mutation carriers. Other families with the R905Q mutation were found to have a similar mild phenotype. In contrast, patients with a 2713C>T (R905W) or a 2713C>G (R905G) mutation had more severe phenotypes. Although all three amino acid substitutions were pathogenic, the R905W and R905G substitutions affected tuberin function more severely than R905Q.

INTERPRETATION

Codon 905 missense mutations in TSC2 are relatively common. The TSC2 R905Q mutation is associated with unusually mild disease, consistent with functional studies. Combined with previous reports, it is apparent that certain TSC2 missense mutations are associated with a mild form of tuberous sclerosis, which in many patients does not meet standard diagnostic criteria. These findings have implications for the large number of patients with limited clinical features of TSC and for genetic counseling in these families.

Molecular and clinical analyses of 84 patients with tuberous sclerosis complex

BACKGROUND

Tuberous sclerosis complex (TSC) is an autosomal dominant disease characterized by the development of multiple hamartomas in many internal organs. Mutations in either one of 2 genes, TSC1 and TSC2, have been attributed to the development of TSC. More than two-thirds of TSC patients are sporadic cases, and a wide variety of mutations in the coding region of the TSC1 and TSC2 genes have been reported.

METHODS

Mutational analysis of TSC1 and TSC2 genes was performed in 84 Taiwanese TSC families using denaturing high-performance liquid chromatography (DHPLC) and direct sequencing.

RESULTS

Mutations were identified in a total of 64 (76 %) cases, including 9 TSC1 mutations (7 sporadic and 2 familial cases) and 55 TSC2 mutations (47 sporadic and 8 familial cases). Thirty-one of the 64 mutations found have not been described previously. The phenotype association is consistent with findings from other large studies, showing that disease resulting from mutations to TSC1 is less severe than disease due to TSC2 mutation.

CONCLUSION

This study provides a representative picture of the distribution of mutations of the TSC1 and TSC2 genes in clinically ascertained TSC cases in the Taiwanese population. Although nearly half of the mutations identified were novel, the kinds and distribution of mutation were not different in this population compared to that seen in larger European and American studies.

Mental retardation and relation to seizure and tuber burden in tuberous sclerosis complex

In patients with tuberous sclerosis complex (TSC), the high rates of mental retardation are associated with cortical tubers, seizure activity, and genetic factors. The goal of the study was to investigate the relationship between bilateral cortical tubers and seizure variables and mental retardation in individuals with TSC. The records of 27 patients with TSC (age 6 months to 33 years) undergoing neuropsychological assessment and the following clinical variables were examined: bilateral versus non-bilateral cortical tubers, the age of seizure onset, and presence of infantile spasms. Results were statistically analyzed. Bilateral cortical tubers (p=0.02) and early age of seizure onset (p=0.04) were significantly related to impaired cognitive functioning. Only one of the seven patients with normal cognitive functioning had bilateral tubers, whereas 13/21 patients with intellectual impairment had bilateral tubers. Patients with normal cognitive functioning experienced a mean age of seizure onset after 6 years. A trend was observed between infantile spasms and cognitive functioning (p=0.06); the lack of statistical significance likely reflects the small sample size. Neither age nor gender was related to cognitive status. Further investigation incorporating additional neuroimaging factors, antiepileptic treatment effects, and genetic variables, is needed.

Mutational analysis of TSC1 and TSC2 in Korean patients with tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by a broad phenotypic spectrum that includes seizures, mental retardation, renal dysfunction and dermatological abnormalities. TSC is caused by mutations affecting either of the tumor-suppressor genes TSC1 and TSC2. At least 495 mutations of TSC1 and TSC2 have been reported. Twenty-two males and 22 females who were diagnosed with TSC at the Seoul National University Children's Hospital between 1982 and 2002 were enrolled in the study. Forty-four patients were from different families and included nine familial cases and 35 sporadic cases. Denaturing high performance liquid chromatography and DNA sequencing analysis of TSC1 and TSC2 revealed 13 types of mutations (30%). One novel mutation of TSC1 and nine novel mutations of TSC2 were identified. The TSC1 mutation and one of the nine TSC2 mutations were missense mutations and seven of the nine TSC2 mutations caused truncation of proteins. One novel single nucleotide substitution was identified at the consensus splicing donor site of exon 39 (c.5,069-1G>A). This mutation is predicted to cause a splicing error. Of the TSC2 mutation loci, the correlation with cardiac rhabdomyoma was more significant when the mutation was in the C-terminal part of tuberin than the N-terminal part. This is the first extensive mutational analysis of TSC1 and TSC2 in Korean TSC patients.