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PubMed1998

A role of the tuberous sclerosis gene-2 product during neuronal differentiation.

Tuberous sclerosis is an autosomal dominant disorder. Besides the development of benign growths (hamartomas) in different tissues, one hallmark of this disease is the presence of highly epileptogenic dysplastic lesions in the cerebral cortex (tubers) composed of abnormal shaped neurones. Patients often show evidence of severe mental retardation. Linkage analysis revealed two disease-determining genes on chromosome 9 and chromosome 16. The TSC2 gene on chromosome 16 encodes a 1784-amino acid putative tumour suppressor protein, tuberin, that functions as a GTPase-activating protein. Here we show that tuberin expression is upregulated upon induction of neuronal differentiation in the neuroblastoma cell lines SK-N-SH and LAN-1. This upregulation occurs at post-transcriptional level and is independent of the proliferation status. TSC2 expression is unaffected during differentiation of C2C12 myoblasts into myotubes and of F9 embryonal carcinoma cells into cells resembling parietal endoderm. Antisense inhibition of tuberin expression in SK-N-SH or LAN-1 cells inhibits neuronal differentiation, but does not affect the differentiation of F9 cells. Ectopic overexpression of TSC2 not only reverts the antisense-associated phenotype but furthermore accelerates the neuronal differentiation process. Our data show for the first time that tuberin plays a critical role in neuronal differentiation. Such role is consistent with the phenotype of tuberous sclerosis patients, who inherit one defective TSC2 allele, and frequently lose the remaining normal allele in many of the tubers/hamartomas which develop in the central nervous system of these patients.

Animals↗
PubMed1998

Loss of function of the tuberous sclerosis 2 tumor suppressor gene results in embryonic lethality characterized by disrupted neuroepithelial growth and development.

Germline defects in the tuberous sclerosis 2 (TSC2) tumor suppressor gene predispose humans and rats to benign and malignant lesions in a variety of tissues. The brain is among the most profoundly affected organs in tuberous sclerosis (TSC) patients and is the site of development of the cortical tubers for which the hereditary syndrome is named. A spontaneous germline inactivation of the Tsc2 locus has been described in an animal model, the Eker rat. We report that the homozygous state of this mutation (Tsc2(Ek/Ek)) was lethal in mid-gestation (the equivalent of mouse E9.5-E13.5), when Tsc2 mRNA was highly expressed in embryonic neuroepithelium. During this period homozygous mutant Eker embryos lacking functional Tsc2 gene product, tuberin, displayed dysraphia and papillary overgrowth of the neuroepithelium, indicating that loss of tuberin disrupted the normal development of this tissue. Interestingly, there was significant intraspecies variability in the penetrance of cranial abnormalities in mutant embryos: the Long-Evans strain Tsc2(Ek/Ek) embryos displayed these defects whereas the Fisher 344 homozygous mutant embryos had normal-appearing neuroepithelium. Taken together, our data indicate that the Tsc2 gene participates in normal brain development and suggest the inactivation of this gene may have similar functional consequences in both mature and embryonic brain.

Animals↗
PubMed1995

Identification of tuberin, the tuberous sclerosis-2 product. Tuberin possesses specific Rap1GAP activity.

Tuberous sclerosis (TSC) is a human genetic syndrome characterized by the development of benign tumors in a variety of tissues, as well as rare malignancies. Two different genetic loci have been implicated in TSC; one of these loci, the tuberous sclerosis-2 gene (TSC2), encodes an open reading frame with a putative protein product of 1784 amino acids. The putative TSC2 product (tuberin) contains a region of limited homology to the catalytic domain of Rap1GAP. We have generated antisera against the N-terminal and C-terminal portions of tuberin, and these antisera specifically recognize a 180-kDa protein in immunoprecipitation and immunoblotting analyses. A wide variety of human cell lines express the 180-kDa tuberin protein, and subcellular fractionation revealed that most tuberin is found in a membrane/particulate (100,000 x g) fraction. Immunoprecipitates of native tuberin contain an activity that specifically stimulates the intrinsic GTPase activity of Rap1a. These results were confirmed in assays with a C-terminal fragment of tuberin, expressed in bacteria or Sf9 cells. Tuberin did not stimulate the GTPase activity of Rap2, Ha-Ras, Rac, or Rho. These results suggest that the loss of tuberin leads to constitutive activation of Rap1 in tumors of patients with tuberous sclerosis.

Cell Compartmentation↗
PubMed2004

Critical role of T-loop and H-motif phosphorylation in the regulation of S6 kinase 1 by the tuberous sclerosis complex.

The tuberous sclerosis gene products Tsc1 and Tsc2 behave as tumor suppressors by restricting cell growth, a function conserved among metazoans. Recent evidence has indicated that hyperactivation of S6 kinase 1 (S6K1) may represent an important biochemical change in the development of tuberous sclerosis-associated lesions. We show here that deletion of either Tsc1 or Tsc2 or expression of the Rheb (Ras homolog enriched in brain) GTPase leads to hyperphosphorylation of S6K1 at a subset of regulatory sites, particularly those of two essential residues functionally conserved among AGC superfamily serine/threonine kinases, i.e. the activation loop (T-loop; Thr-229) and the hydrophobic motif (H-motif; Thr-389). These sites are reciprocally and dose-dependently regulated when S6K1 is coexpressed with the Tsc1-Tsc2 complex. Mutations that render S6K1 mTOR (mammalian target of rapamycin)-resistant also protect S6K1 activity and phosphorylation from down-regulation by Tsc1/2. We demonstrate that two disease-associated mutations in Tsc2 fail to negatively regulate S6K1 activity concomitant with a failure to modify T-loop and H-motif phosphorylation. Finally, we identify one pathological Tsc2 mutation that retains its ability to negatively regulate S6K1, suggesting that, in some cases, tuberous sclerosis may develop independently of S6K1 hyperactivation. These results also highlight the importance of dual control of T-loop and H-motif phosphorylation of S6K1 by the Tsc1-Tsc2 complex.

Amino Acid Sequence↗
PubMed2005

Multiple cardiac rhabdomyomas as a sole symptom of tuberous sclerosis complex: case report with molecular confirmation.

We report a child in whom multiple cardiac rhabdomyomas were identified on routine fetal ultrasonography. Molecular genetic studies identified the TSC2 gene missense mutation (E36; 4672 G>A, 1558 E>K TSC2). Both general and neurodevelopment of the patient have been normal. When last examined at age 6 years, he had no skin manifestations of tuberous sclerosis complex. Computed tomography of the brain revealed two periventricular calcifications consistent with the molecular diagnosis. This is the first report of molecularly confirmed tuberous sclerosis complex in a child with multiple cardiac rhabdomyomas and no other clinical manifestations of the disease. We propose that all cases of multiple cardiac rhabdomyomas in an infant be given a tentative diagnosis of tuberous sclerosis complex.

Brain↗
PubMed1999

Prenatal diagnosis of tuberous sclerosis with intracerebral signs at 14 weeks' gestation.

We report the ultrasound detection of cranial abnormalities at 14 weeks' gestation in a fetus subsequently confirmed as having tuberous sclerosis using DNA linkage analysis within the affected family. The presence of asymmetrical ventricular enlargement persisted antenatally. Magnetic resonance imaging at 26 weeks indicated the possibility of poor gyral formation consistent with a neuronal migration disorder. Cardiac rhabdomyomata were not visualized on ultrasound scan until 30 weeks' gestation. Postnatal cranial ultrasound confirmed the significant neuropathology which was manifested by severe developmental delay and intractable fits in the child. The potential benefits of earlier diagnosis of tuberous sclerosis by cranial imaging are discussed, although in this patient the routine booking scan resulted in a path of prenatal diagnosis being undertaken which had originally been declined. A mechanism is proposed to explain the variable expression of tuberous sclerosis within this family based on altered TSC2 activity affecting neuronal migration.

Adult↗
PubMed1990

Incidence of tuberous sclerosis in patients with cardiac rhabdomyoma.

Cardiac rhabdomyoma, a rare benign tumor often detected in infancy, is frequently associated with tuberous sclerosis. This association is commonly stated to occur in 50% of all cases of cardiac rhabdomyoma. Recently at our institution, the prenatal detection of a cardiac rhabdomyoma in a fetus at no known risk for tuberous sclerosis emphasized the need to determine the frequency of association in order to provide accurate diagnosis and counseling in such situations. After a review of reported cases and review of patients from our institution diagnosed to have cardiac rhabdomyoma, we estimate that 51-86% of cardiac rhabdomyomas are associated with tuberous sclerosis. We present the results of our literature and case review.

Female↗
PubMed1993

Thyroid dysgenesis and the dysplasia hypothesis in tuberous sclerosis.

Thyroid dysfunction is rare in tuberous sclerosis, although papillary adenomas (hamartomas) of the thyroid gland have been reported in a few autopsy cases. We describe a child with tuberous sclerosis and primary congenital hypothyroidism secondary to a dysgenetic thyroid gland. To our knowledge, this association has not been reported previously. Although the association of these two disorders in one patient may be merely coincidence, we speculate that the dysgenetic thyroid gland in this patient may represent a "hamartia" as a consequence of the tuberous sclerosis gene.

Congenital Hypothyroidism↗
PubMed2004

Neuroepileptic correlates of autistic symptomatology in tuberous sclerosis.

Tuberous sclerosis is a genetic condition that is strongly associated with the development of an autism spectrum disorder. However, there is marked variability in expression, and only a subset of children with tuberous sclerosis develop autism spectrum disorder. Clarification of the mechanisms that underlie the association and variability in expression will potentially throw light on the biological processes involved in the etiology of idiopathic forms of autism spectrum disorder. Current evidence indicates that the likelihood of a child with tuberous sclerosis developing an autism spectrum disorder is greater if the child has a mutation in the TSC2 gene, although autism can and does develop in children with TSC1 mutations. The likelihood is also greater if the child has early-onset infantile spasms that are difficult to control, especially if there is an epileptiform focus in the temporal lobes. The emerging evidence is consistent with the notion that early onset electrophysiological disturbances within the temporal lobes (and perhaps other locations) has a deleterious effect on the development and establishment of key social cognitive representations concerned with processing social information, perhaps especially from faces. However, alternative mechanisms to account for the findings cannot yet be ruled out. Future research will have to employ prospective longitudinal designs and treatment trials to clarify the processes involved.

Autistic Disorder↗
PubMed2004

Pulmonary involvement in tuberous sclerosis.

Tuberous sclerosis is a neurocutaneous syndrome involving many tissues. Pulmonary involvement is rare. Pulmonary cases are usually women of child-bearing age who present with spontaneous pneumothorax or progressive dyspnea. In childhood and, even more, in male patients, pulmonary involvement by tuberous sclerosis is exceptional. We report on a 4-year-old male patient diagnosed in the first months of life with tuberous sclerosis with predominantly respiratory symptoms (frequently with acute RDS criteria), in whom lung involvement was pathologically confirmed.

Child, Preschool↗
PubMed1996

Characterization of a kinesin-related gene ATSV, within the tuberous sclerosis locus (TSC1) candidate region on chromosome 9Q34.

In the search for candidate genes for the tuberous sclerosis (TSC1) disease locus on chromosome 9q34, we have isolated an overlapping series of 22 plasmid and phage cDNA clones covering nearly 7 kb and with an open reading frame of 5070 bp encoding a protein of 1690 amino acids. The putative protein product is a member of the kinesin superfamily and is homologous to the mouse KIF1A and the Caenorhabditas elegans unc-104 genes. Both KIF1A and unc-104 function in the anterograde axonal transport of synaptic vesicles. The human homolog is therefore termed H-ATSV (axonal transporter of synaptic vesicles, HGMW-approved nomenclature ATSV) Screening of DNA from 107 tuberous sclerosis patients and 80 unaffected individuals with H-ATSV cDNA probes by pulsed-field gel electrophoresis/Southern blotting following digestion by rare-cutting methylation-sensitive restriction enzymes showed variant banding patterns in three patients with tuberous sclerosis. However, further analysis indicated that these variant fragments represent a rare polymorphism probably associated with methylation of clustered restriction sites. There is no evidence to support H-ATSV as a candidate gene for TSC1.

Amino Acid Sequence↗
PubMedDate not supplied

Angiomyolipomas of the liver in tuberous sclerosis.

Although the association of tuberous sclerosis and renal angiomyolipomas is well established, the occurrence of hepatic hamartomatous lesions in this disease is less well documented. We describe two cases of tuberous sclerosis with associated multiple intrahepatic angiomyolipomas, and we review the literature on this subject. Radiologically, angiomyolipomas can range from entirely lipomatous to completely solid, features which are present in our cases. A characteristic finding of the hepatic involvement in this disease appears to be the multiplicity of the lesions. We suggest that in the setting of tuberous sclerosis it is reasonable to assume that intrahepatic lesions represent angiomyolipomas. However, in nontuberous sclerosis patients with similar findings malignancy cannot be excluded.

Adult↗
PubMed1996

Neurological manifestations of tuberous sclerosis complex.

CNS lesions of tuberous sclerosis complex (TSC) are due to a developmental disorder of neurogenesis and neuronal migration. MRI studies provide excellent in vivo demonstration of the various pathologic lesions. Symptoms of cortical tubers may include seizures, mental retardation, learning disabilities, and abnormal behavior. Seizures have a focal or multifocal origin, this clinical feature depending on the localization of the cortical tubers. Epilepsy associated with TSC is often intractable, but seizure control has benefited from the introduction of the new antiepileptic drugs. Carefully selected drug-resistant patients can be assessed with intensive monitoring as candidates for surgical removal of epileptogenic lesions. The success of epilepsy surgery is predicated on the clear identification of epileptogenic foci.

Anticonvulsants↗
PubMed1987

Electron microscopy as a means for carrier detection and genetic counselling in families at risk of tuberous sclerosis.

In otherwise asymptomatic parents of two unrelated children severely affected with tuberous sclerosis (TS), the ultrastructure of hypomelanotic skin lesions was investigated. In the hypomelanotic macules of both mothers of the two families, the population density of melanocytes was normal, melanization, however, was markedly suppressed. Therefore, these macules represent typical "white leaf-shaped macules" characteristic of tuberous sclerosis. Especially by applying the dihydroxyphenylalanine (DOPA) reaction to the ultrastructural level, it was possible to separate the TS-macules from the vitiliginous lesions of one father with a decrease of functional melanocytes as well as from other congenital circumscribed hypomelanoses. Thus electron microscopy in combination with the DOPA reaction may be helpful in recognizing a "forme fruste" of the dominantly inherited tuberous sclerosis (i.e. identification of white leaf-shaped macules) to enable genetic counselling and family planning by marking carriers of the mutant TS gene amongst the relatives of a patient and to exclude a sporadic mutation.

Adult↗
PubMed1992

Morphology and function of capillary networks in subregions of the rat tuber cinereum.

The differentiated cytology, cytochemistry, and functions within subdivisions of the tuber cinereum prompted this morphometric and physiological investigation of capillaries in the medium eminence and arcuate nucleus of albino rats. Morphometric studies established that the external zone of the median eminence had 3-5 times the number and surface area of true and sinusoidal capillaries than the internal or subependymal median eminence zones, or either of two subdivisions examined in the arcuate nucleus. Type-I true capillaries, around which Virchow-Robin spaces comprise 1% of arcuate tissue area, were situated proximally to the median eminence border. This finding is consistent with a premise that confluent pericapillary spaces enable infiltration of arcuate neurons by factors from capillary blood from the median eminence or Virchow-Robin spaces. Physiologically, the rate of penetration across the median eminence capillaries by blood-borne [14C]alpha-amino-isobutyric acid (a neutral amino acid used as a capillary permeability tracer) was 142 times greater than for capillaries in the distal arcuate nucleus within 12 s of tracer administration. A new finding was that the proximal arcuate nucleus had a permeability x surface area product of 69 microliters g-1 min-1, 34 times greater than that in more distal aspects of the tuber where blood-brain barrier properties exist. We also found that the microcirculatory transit time of a plasma space marker, [14C]sucrose, was considerably longer (1.2 s) in the median eminence and proximal arcuate nucleus than in the distal arcuate or ventromedial nucleus (0.4 s). By virtue of its high capillary permeability and extensive blood-tissue surface area, including the wide Virchow-Robin spaces, the median eminence external zone could be a gateway for flooding other tuberal compartments with blood-borne factors. This effect may be compounded by capillary bed specializations in the proximal arcuate nucleus where Type-I true capillaries, Type-III sinusoids, and pericapillary spaces are confluent with those in the median eminence. The results indicate that the proximal arcuate parenchyma could be exposed to circulating neuroactive substances on a moment-to-moment basis.

Animals↗
PubMed1987

MRI evaluation of tuberous sclerosis.

The authors present four cases of tuberous sclerosis examined with MRI. The patho-anatomic aspects are reviewed and analysed with respect to MRI data. MRI appears superior to the CT particularly for imaging of cortical tubers, cystic lesions, and heterotopic clusters; these last two features were never described with MRI before. Here is also presented the second progressive case of giant intracranial aneurysm associated with tuberous sclerosis.

Adult↗
PubMed1981

Splenic involvement in tuberous sclerosis. Report of three cases.

Three cases of tuberous sclerosis in neonates were found to have focal, frequently perivascular, collections of large cells with abundant eosinophilic cytoplasm. These cells resembled those found in brain lesions of tuberous sclerosis but did not stain for acidic protein. Ultrastructurally, they were characterized by many membrane bound cytoplasmic bodies, 90 to 270 nm in diameter, with amorphous contents. Filaments were not demonstrated. Their appearance is considered most consistent with histiocytic origin. Large cells with a histiocytic appearance and a superficial resemblance to those seen in the brain in tuberous sclerosis, but a different ultrastructure and reaction to GFAP staining, may be found in the spleen of neonates with this disease.

Histiocytes↗
PubMed1993

Renal cystic disease in the tuberous sclerosis complex.

Renal cysts are relatively common in tuberous sclerosis, occasionally causing severe cystic disease with renal failure. Although the imaging features and gross appearances resemble dominant polycystic kidney disease, the histopathological appearances are distinctive, perhaps unique, differing from appearances in other forms of renal cystic disease. The cysts are lined with hypertrophic and hyperplastic cells that probably cause the cysts by obstructing lumina. The renal abnormality may be inherent in tuberous sclerosis, although inconstantly expressed. Renal enlargement is sometimes the first recognized expression of tuberous sclerosis, and the occurrence of renal cysts in a child with seizures and developmental retardation leads to a strong suspicion of the diagnosis.

Adolescent↗