Evidence for population variation in TSC1 and TSC2 gene expression

The clinical interface of tuberous sclerosis complex and autism spectrum disorder: insights and future directions

BACKGROUND AND OBJECTIVE

Tuberous sclerosis complex (TSC) is a hereditary disorder that leads to tumor growth in various organs. Manifestations from mutations in the TSC1 or TSC2 genes comprise seizures, developmental delay, and skin abnormalities. This literature search has been dedicated to emphasizing the critical role of early diagnosis and the formulation of individualized plans for this target population with co-occurring TSC and Autism Spectrum Disorder (ASD).

EXPERIMENTAL PROCEDURE

Behavioral and developmental tests can evaluate ASD symptoms; neuroimaging methods like functional MRI and PET scans can identify brain abnormalities, and molecular genetic analysis can detect TSC1/TSC2 mutations. Differential Diagnostic Approach These include medical histories and physical examinations to consider that ASD and TSC present the same symptoms.

RESULTS

Although 90% of TSC patients are reported to have TSC-associated neuropsychiatric disorders, 30-50% of patients fulfil the clinical criteria of ASD. In comparison, the estimate for the rate of ASD prevalence in TSC patients ranges from 17 to 63%, with the characteristics of infantile spasms and early-onset epilepsy. The diagnosis is further challenged by the fact that there are shared symptoms between both, namely seizures and intellectual impairment.

CONCLUSION

The shared symptoms between TSC and ASD suggest the need for multidisciplinary approaches in both diagnosis and treatment. A personalized therapeutic plan should include behavioral therapy, medication with Everolimus, mammalian target of rapamycin (mTOR) inhibitors, and advanced neuroimaging. The future of research in biomarkers, molecular medicines, and improving diagnostic protocols holds great promise for optimizing patient care and treatment options.

The TSC2 c.2742+5G>A variant causes variable splicing changes and clinical manifestations in a family with tuberous sclerosis complex

Background

Tuberous sclerosis complex (TSC) is a genetic, variably expressed, multisystem disease characterized by benign tumors. It is caused by pathogenic variants of the TSC complex subunit 1 gene (TSC1) and the TSC complex subunit 2 gene (TSC2). Genetic testing allows for early diagnosis, genetic counseling, and improved outcomes, but it did not identify a pathogenic variant in up to 25% of all TSC patients. This study aimed to identify the disease-causing variant in a Han-Chinese family with TSC.

Methods

A six-member, three-generation Han-Chinese family with TSC and three unrelated healthy women were recruited. A comprehensive medical examination, a 3-year follow-up, whole exome sequencing, Sanger sequencing, and segregation analysis were performed in the family. The splicing analysis results obtained from six in silico tools, minigene assay, and patients' lymphocyte messenger RNA were compared, and quantitative reverse transcription PCR was used to confirm the pathogenicity of the variant.

Results

Two affected family members had variable clinical manifestations including a rare bilateral cerebellar ataxia symptom. The 3-year follow-up results suggest the effects of a combined treatment of anti-epilepsy drugs and sirolimus for TSC-related epilepsy and cognitive deficits. Whole exome sequencing, Sanger sequencing, segregation analysis, splicing analysis, and quantitative reverse transcription PCR identified the TSC2 gene c.2742+5G>A variant as the genetic cause. This variant inactivated the donor splice site, a cryptic non-canonical splice site was used for different splicing changes in two affected subjects, and the resulting mutant messenger RNA may be degraded by nonsense-mediated decay. The defects of in silico tools and minigene assay in predicting cryptic splice sites were suggested.

Conclusions

This study identified a TSC2 c.2742+5G>A variant as the genetic cause of a Han-Chinese family with TSC and first confirmed its pathogenicity. These findings expand the phenotypic and genetic spectrum of TSC and may contribute to its diagnosis and treatment, as well as a better understanding of the splicing mechanism.

Optimization and high-density array of stereoelectroencephalography-guided radiofrequency thermocoagulation for the treatment of pediatric tuberous sclerosis complex with epilepsy

BACKGROUND

Tuberous sclerosis complex (TSC) is an autosomal dominant neurocutaneous syndrome involved in many organ systems. At the same time, epilepsy is the most common manifestation and more than 50% of TSC patients present with intractable epilepsy. This study investigated the efficacy and safety of optimized and high-density stereoelectroencephalography (SEEG) guided radiofrequency thermocoagulation (RF-TC) in treating TSC-related epilepsy.

METHODS

Nine TSC children with refractory epilepsy were treated with first-stage SEEG-Guided RF-TC, and four underwent second-stage-optimized high-density array of SEEG-Guided RF-TC. Patients' clinical data and postoperative outcomes were analyzed retrospectively.

RESULTS

The patients' median age at surgery was 4 years and 2 month (range from 3 years and 5 month to 16 years and 7 month). The mean age at surgery was 6.7 years old. Eight in 9 (88.9%) patients achieved complete remission after the final operation at half-year follow-up. Of seven patients with final postoperative time beyond 1 year, 6 (85.7%) reached completely seizure-free. No severe or long-term neurologic impairment existed in all nine patients.

CONCLUSION

Optimized high-density array of SEEG-guided RF-TC is a safe and highly effective approach and can be an alternative application applied for TSC patients with refractory epilepsy.

Genetics in Epilepsy

The presence of unprovoked, recurrent seizures, particularly when drug resistant and associated with cognitive and behavioral deficits, warrants investigation for an underlying genetic cause. This article provides an overview of the major classes of genes associated with epilepsy phenotypes divided into functional categories along with the recommended work-up and therapeutic considerations. Gene discovery in epilepsy supports counseling and anticipatory guidance but also opens the door for precision medicine guiding therapy with a focus on those with disease-modifying effects.

Neuron-Glia Interactions Increase Neuronal Phenotypes in Tuberous Sclerosis Complex Patient iPSC-Derived Models

Tuberous sclerosis complex (TSC) is a rare neurodevelopmental disorder resulting from autosomal dominant mutations in the TSC1 or TSC2 genes, leading to a hyperactivated mammalian target of rapamycin (mTOR) pathway, and gray and white matter defects in the brain. To study the involvement of neuron-glia interactions in TSC phenotypes, we generated TSC patient induced pluripotent stem cell (iPSC)-derived cortical neuronal and oligodendrocyte (OL) cultures. TSC neuron mono-cultures showed increased network activity, as measured by calcium transients and action potential firing, and increased dendritic branching. However, in co-cultures with OLs, neuronal defects became more apparent, showing cellular hypertrophy and increased axonal density. In addition, TSC neuron-OL co-cultures showed increased OL cell proliferation and decreased OL maturation. Pharmacological intervention with the mTOR regulator rapamycin suppressed these defects. Our patient iPSC-based model, therefore, shows a complex cellular TSC phenotype arising from the interaction of neuronal and glial cells and provides a platform for TSC disease modeling and drug development.

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TSC neuron mono-cultures show an increase in network activity and dendritic branching

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TSC co-cultures show hypertrophy and an increase in axonal length and OL proliferation

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mTOR regulators normalize TSC neuronal and glial phenotypes

A novel TSC2 missense variant associated with a variable phenotype of tuberous sclerosis complex: case report of a Chinese family

Background

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder characterized by the development of hamartomas in multiple organs, including the brain, heart, skin, kidney, lung and retina. A diagnosis of TSC is established with a recently revised clinical/radiological set of criteria and/or a causative mutation in TSC1 or TSC2 gene.

Case presentation

We report a Chinese TSC family with two siblings presenting with multiple hypomelanotic macules, cardiac rhabdomyomas and cortical tubers associated with a small subependymal nodule. The older child had seizures. A novel heterozygous missense variant in the TSC2 gene (c.899G > T, p.G300 V) was identified and shown to be inherited from their father as well as paternal grandfather, both of whom presented with variable TSC-associated signs and symptoms.

Conclusion

We identified a novel heterozygous TSC2 variant c.899G > T as the causative mutation in a Chinese family with TSC, resulting in wide intrafamilial phenotypic variability. Our study illustrates the importance of clinical evaluation and genetic testing for family members of the patient affected with TSC.

First five generations Chinese family of tuberous scleroses complex due to a new mutation of the TSC1 gene

Tuberous scleroses complex (TSC) is a rare neurocutaneous syndrome and has autosomal dominant inheritance. However, larger family with TSC is very rare. Here, we report the first five generations family with TSC from China, and localize the pathogenic gene. A boy with TSC and epilepsy underwent preoperative evaluation and epileptic surgery. His TSC family history was gotten, and the clinical data of a Chinese family with TSC were collected in 2016. Complete exons sequencing was performed in the proband and his parents, and whole exons sequence of TSC was performed in the other family members. The family showed autosomal dominant inheritance, and it was the largest reported family with TSC. In this pedigree, there were 14 patients in 5 generations, but only 1 case with epilepsy in them. All of examined patients had TSC 1 gene exon 15 c.1846delG p.A616Pfs^*13 mutation. In conclusion, TSC patients with TSC 1 deletion presented mild neurological symptom and rendered larger family.

Radiobiological Characterization of Tuberous Sclerosis: a Delay in the Nucleo-Shuttling of ATM May Be Responsible for Radiosensitivity

The tuberous sclerosis complex (TSC) syndrome is associated with numerous cutaneous pathologies (notably on the face), epilepsy, intellectual disability and developmental retardation and, overall, high occurrence of benign tumors in several organs, like angiofibromas, giant cell astrocytomas, renal angiomyolipomas, and pulmonary lymphangioleiomyomatosis. TSC is caused by mutations of either of the hamartin or tuberin proteins that are mainly cytoplasmic. Some studies published in the 1980s reported that TSC is associated with radiosensitivity. However, its molecular basis in TSC cells is not documented enough. Here, we examined the functionality of the repair and signaling of radiation-induced DNA double-strand breaks (DSB) in fibroblasts derived from TSC patients. Quiescent TSC fibroblast cells elicited abnormally low rate of recognized DSB reflected by a low yield of nuclear foci formed by phosphorylated H2AX histones. Irradiated TSC cells also presented a delay in the nucleo-shuttling of the ATM kinase, potentially due to a specific binding of ATM to mutated TSC protein in cytoplasm. Lastly, TSC fibroblasts showed abnormally high MRE11 nuclease activity suggesting genomic instability. A combination of biphosphonates and statins complemented these impairments by facilitating the nucleoshuttling of ATM and increasing the yield of recognized DSB. Our results showed that TSC belongs to the group of syndromes associated with low but significant defect of DSB signaling and delay in the ATM nucleo-shuttling associated with radiosensitivity.

Tsc1 haploinsufficiency is sufficient to increase dendritic patterning and Filamin A levels

Most individuals with tuberous sclerosis complex (TSC) are born with a mutant allele of either TSC1 or TSC2 and a mosaic of psychological and cognitive defects. Tsc1 loss of heterozygosity contributes to severe dendritic abnormalities that are rescued by normalizing the levels of the actin-cross linking protein, Filamin A (FLNA). However, it is unclear whether dendrites and FLNA levels are abnormal in an heterozygote Tsc1 condition. Here, we examined dendritic morphology and FLNA levels in the olfactory bulb of Tsc1 wild type and heterozygote mice. Using in vivo neonatal electroporation to label newborn neurons followed by sholl analysis, we found that Tsc1 haploinsufficiency is associated with increased dendritic complexity and total dendritic length as well as increased FLNA levels. Since reducing FLNA levels has been shown to decrease Tsc1(+/-) dendritic complexity, these data suggest that increased FLNA levels in Tsc1(+/-) mice contribute to abnormal dendritic patterning in the Tsc1 heterozygote condition of individuals with TSC.

Clinical value of prenatal echocardiographic examination in the diagnosis of fetal cardiac tumors

The aim of the present study was to explore the clinical value of prenatal echocardiographic examination in the diagnosis of fetal cardiac tumors. In total, the cases of 8 fetuses with fetal cardiac tumors, which were identified by prenatal ultrasound examination in The First Affiliated Hospital of Nanchang University between January 2012 and January 2014, were retrospectively analyzed. The size, shape, location, activity and hemodynamic changes of the lesions were described in detail, and the patients were followed up. Out of the 8 identified cases of fetal cardiac tumors, 2 fetuses contained tumors only in the left ventricular cavity and 6 fetuses contained tumors of the left and right ventricular cavities, interventricular septum and apex of the heart. Overall, 5 of the 8 female patients requested termination of the pregnancy and labor was induced. The fetuses were pathologically confirmed to possess rhabdomyoma. In addition, 1 patient was followed-up for 5 weeks, and the tumor in the fetal heart cavity was found to have enlarged and developed in multiple regions when follow-up was performed. The patient then requested termination of the pregnancy and labor was induced. The fetus was pathologically confirmed to possess rhabdomyoma. The remaining 2 patients insisted on continuation of the pregnancy and the fetuses were followed up during gestation and subsequent to birth by echocardiographic examination. Prenatal echocardiography may precisely position and diagnose occupying lesions of the fetal heart, which is of considerable value in clinical decision making and instruction for treatment.

Correlation between tuberous sclerosis complex 2 and glycogen synthase kinase 3 beta levels, and outcomes of patients with hepatocellular carcinoma treated by hepatectomy

AIM

Tuberous sclerosis complex 2 (TSC2), a tumor suppressor, may play an essential role in the regulation of cell growth and cell survival under energy stress conditions. In addition, TSC2 may act in concert with Wnt and energy signals by additional phosphorylation of glycogen synthase kinase 3β (GSK3β) to regulate cell growth. The expression levels and function of TSC2 and GSK3β in hepatocellular carcinoma (HCC) remain unclear.

METHODS

The protein levels of TSC2 and GSK3β were measured by immunohistochemistry in normal liver (n = 20), HCC (n = 80) and pericancerous tissues (n = 80). The correlations between TSC2, and GSK3β levels, clinicopathological features and patient survival were also analyzed.

RESULTS

The protein levels of TSC2 and GSK3β in HCC tissues were significantly lower than that in normal liver tissues and pericancerous tissues (P < 0.05). Decreased TSC2 and GSK3β expression was found to be significantly correlated with advanced clinicopathological characteristics and poor prognosis. The results also showed that TSC2 protein levels were associated with GSK3β expression in HCC specimens.

CONCLUSION

This is the first demonstration that the decreases in TSC2 and GSK3β levels may be associated with vascular invasion, histological grade and tumor-node-metastasis classification.

An intronic PICALM polymorphism, rs588076, is associated with allelic expression of a PICALM isoform

BACKGROUND

Although genome wide studies have associated single nucleotide polymorphisms (SNP)s near PICALM with Alzheimer's disease (AD), the mechanism underlying this association is unclear. PICALM is involved in clathrin-mediated endocytosis and modulates Aß clearance in vitro. Comparing allelic expression provides the means to detect cis-acting regulatory polymorphisms. Thus, we evaluated whether PICALM showed allele expression imbalance (AEI) and whether this imbalance was associated with the AD-associated polymorphism, rs3851179.

RESULTS

We measured PICALM allelic expression in 42 human brain samples by using next-generation sequencing. Overall, PICALM demonstrated equal allelic expression with no detectable influence by rs3851179. A single sample demonstrated robust global PICALM allelic expression imbalance (AEI), i.e., each of the measured isoforms showed AEI. Moreover, the PICALM isoform lacking exons 18 and 19 (D18-19 PICALM) showed significant AEI in a subset of individuals. Sequencing these individuals and subsequent genotyping revealed that rs588076, located in PICALM intron 17, was robustly associated with this imbalance in D18-19 PICALM allelic expression (p = 9.54 x 10-5). This polymorphism has been associated previously with systolic blood pressure response to calcium channel blocking agents. To evaluate whether this polymorphism was associated with AD, we genotyped 3269 individuals and found that rs588076 was modestly associated with AD. However, when both the primary AD SNP rs3851179 was added to the logistic regression model, only rs3851179 was significantly associated with AD.

CONCLUSIONS

PICALM expression shows no evidence of AEI associated with rs3851179. Robust global AEI was detected in one sample, suggesting the existence of a rare SNP that strongly modulates PICALM expression. AEI was detected for the D18-19 PICALM isoform, and rs588076 was associated with this AEI pattern. Conditional on rs3851179, rs588076 was not associated with AD risk, suggesting that D18-19 PICALM is not critical in AD. In summary, this analysis of PICALM allelic expression provides novel insights into the genetics of PICALM expression and AD risk.

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.

The ominous sequence in patients with tuberous sclerosis complex

BACKGROUND

The clinical phenotypes and their severity in patients with tuberous sclerosis complex can be quite variable and are sometimes never determined simply by the primary mutation. These make clinically selecting appropriate treatments and predicting disease outcome difficult. In this report, the prognostic ominous sequence was evaluated in association with clinical manifestations and gene mutations.

METHODS

The patients were classified by each renal lesion of angiomyolipomas and polycystic disease. The other clinical manifestations and outcomes of epilepsy, mental retardation, facial angiofibromas, subependymal giant cell astrocytoma, cortical tubers were reviewed and each gene mutations were analyzed in seven unrelated patients.

RESULTS

Two patients with multiple and large proliferative renal angiomyolipoma showed poor clinical outcome than the patients with other renal lesions. These patients presented with progressively proliferative facial angiofibroma, West syndrome, Lennox-Gastaut syndrome, severe mental retardation, subependymal giant cell astrocytoma and they were affected by TSC2 gene mutations.

CONCLUSION

The sequence of progressively proliferative renal angiomyolipoma, facial angiofibroma, West syndrome and TSC2 gene mutations might be prognostic ominous factors.

Epilepsy in TSC: certain etiology does not mean certain prognosis

PURPOSE

Prevalence and long-term outcome of epilepsy in tuberous sclerosis complex (TSC) is reported to be variable, and the reasons for this variability are still controversial.

METHODS

We reviewed the clinical characteristics of patients with TSC who were regularly followed since 2000 at the San Paolo Multidisciplinary Tuberous Sclerosis Centre in Milan, Italy. From patient charts we collected data about age at epilepsy onset, seizure frequency and seizure type, history of infantile spasms (IS), epileptic syndrome, evolution to refractory epilepsy or to seizure freedom and/or medication freedom, electroencephalography (EEG) features, magnetic resonance imaging (MRI) findings, cognitive outcome, and genetic background.

KEY FINDINGS

Among the 160 subjects (120 adults and 40 children), 116 (72.5%) had epilepsy: 57 (35.6%) were seizure-free, and 59 (36.9%) had drug-resistant epilepsy. Most seizure-free patients had a focal epilepsy (89.5%), with 54.4% of them drug resistant for a period of their lives. Epilepsy onset in the first year of life with IS and/or focal seizures was characteristic of the drug-resistant group of patients, as well as cognitive impairment and TSC2 mutation (p < 0.05). A small group of patients (7 patients, 4.4%) experienced a seizure only once; all of them had normal cognition.

SIGNIFICANCE

Although epilepsy management can be challenging in TSC, more than one third of patients had their seizures controlled: through monotherapy in 56% and by polytherapy in 32%. Moreover, 12% of the patients became seizure-free and were off medication. Identifying predictive features of epilepsy and cognitive outcome can ensure better management for patients with TSC and delineate genotype-phenotype correlations.

Everolimus in the treatment of subependymal giant cell astrocytomas, angiomyolipomas, and pulmonary and skin lesions associated with tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder caused by inactivating mutations in either the TSC1 or TSC2 genes. It is characterized by the development of multiple, benign tumors in several organs throughout the body. Lesions occur in the brain, kidneys, heart, liver, lungs, and skin and result in seizures and epilepsy, mental retardation, autism, and renal and pulmonary organ system dysfunction, as well as other complications. Elucidation of the molecular pathways and etiological factors responsible for causing TSC has led to a paradigm shift in the management and treatment of the disease. TSC1 or TSC2 mutations lead to constitutive upregulation of the mammalian target of rapamycin pathway, which affects many cellular processes involved in tumor growth. By targeting mammalian target of rapamycin with everolimus, an orally active rapamycin derivative, clinically meaningful and statistically significant reductions in tumor burden have been achieved for the main brain (subependymal giant cell astrocytoma) and renal manifestations (angiomyolipoma) associated with TSC. This review provides an overview of TSC, everolimus, and the clinical trials that led to its approval for the treatment of TSC-associated subependymal giant cell astrocytoma and renal angiomyolipoma.

Mutational analyses of the TSC1 and TSC2 genes in cases of tuberous sclerosis complex in Chinese Han children

Tuberous sclerosis complex (TSC) is an autosomal dominant neurogenetic disorder characterized by hamartomas in multiple organs and is caused by a wide spectrum of mutations in 1 of 2 causative genes (TSC1 or TSC2). Here, we present mutational analyses of the TSC1 and TSC2 genes in 4 cases of TSC in Chinese Han children, including 2 familial and 2 sporadic cases, using PCR and DNA sequencing of the entire coding region as well as exon-intron boundaries of these genes. Three mutations were identified in the TSC2 gene. Of these mutations, 2 mutations (c.3312-3313delGA and c.45delT) were novel, and the 3rd mutation (c.5238-5255del) was previously reported in Chinese Han and other populations. These mutations were not present in healthy family members or in 100 unrelated normal controls. The identification of these mutations in this study further expands the spectrum of known TSC2 gene mutations and contributes to prenatal molecular diagnosis and preimplantation genetic testing of TSC.

Skewed allele-specific expression of the NF1 gene in normal subjects: a possible mechanism for phenotypic variability in neurofibromatosis type 1

Neurofibromatosis type 1 is an autosomal dominant disorder characterized by neurocutaneous abnormalities, learning disabilities, and attention-deficit disorder. Neurofibromatosis type 1 symptom severity can be highly variable even within families where all affected members carry the same mutation. We hypothesized that variation in the expression of the normal NF1 allele may be a mechanism that participates in producing variable phenotypes. We performed allelic expression imbalance assays on healthy control individuals to estimate the prevalence of skewed allelic expression of the NF1 gene. Approximately 30% of individuals in our sample population showed significant skewing of allelic expression away from the expected 50:50 ratio, indicating that differential regulation of the NF1 alleles occurs in a high proportion of individuals. Differences of up to 25% in allele-specific expression of the NF1 alleles were identified. In individuals with Neurofibromatosis type 1, who carry a mutant allele (haploinsufficient), this degree of expression skewing may be sufficient to modulate the phenotype.

Emerging treatments in the management of tuberous sclerosis complex

Tuberous sclerosis complex is a genetic disorder characterized by the formation of nonmalignant hamartomas in the brain, heart, skin, kidney, lung, and other organs. It is associated with autism, epilepsy, and other neurocognitive and behavioral disabilities. Wide phenotypic variation occurs in disease severity and natural course: some patients demonstrate minimal effects, e.g., skin changes; others manifest profound seizures and mental retardation. Tuberous sclerosis complex is caused by mutations in either the tuberous sclerosis complex 1 or 2 gene (coding for hamartin and tuberin, respectively). The tuberous sclerosis complex 1/tuberous sclerosis complex 2 protein dimer complex is a crucial inhibitory element in the mammalian target of rapamycin pathway, regulating cell growth and proliferation. Until recently, few options existed, other than surgery, for treating symptoms of tuberous sclerosis complex related to the growth of hamartomas. Increased understanding of the genetic cause of the disease and underlying dysregulation of the mammalian target of rapamycin pathway has led to clinical trials of mammalian target of rapamycin inhibitors, including sirolimus and everolimus. This review gives an overview of tuberous sclerosis complex and its molecular causes, and summarizes results from recent clinical trials of mammalian target of rapamycin inhibitors in patients with the disease.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay: compound heterozygotes for nonsense mutations of the SACS gene

Mutations of the SACS gene have been reported in patients with autosomal recessive spastic ataxia of Charlevoix-Saguenay from Canada (Quebec), Tunisia, Japan, Turkey, Belgium, Italy, Spain, the Netherlands, and Germany. Features that distinguish autosomal recessive spastic ataxia of Charlevoix-Saguenay from other recessive ataxias include sensory motor polyneuropathy and hypermyelinated retinal nerve fibers. We describe the clinical, electrophysiological, and radiological features in 2 white American siblings diagnosed with autosomal recessive spastic ataxia of Charlevoix-Saguenay. The 2 affected children are compound heterozygotes for nonsense mutations of the SACS gene (c. 3484 G>T, p. E 1162 X; and c. 11,707 C>T, p. R 3903 X). We have measured allele-specific SACS mRNA abundance in peripheral blood and show that these specific mutant mRNAs are not degraded. We suggest that in children with early onset cerebellar ataxia and spasticity, ophthalmological examination and nerve conduction testing may guide genetic testing.