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

Analysis of 65 tuberous sclerosis complex (TSC) patients by TSC2 DGGE, TSC1/TSC2 MLPA, and TSC1 long-range PCR sequencing, and report of 28 novel mutations

Tuberous sclerosis complex (TSC) is a severe autosomal-dominant disorder characterized by the development of benign tumors (hamartomas) in many organs. It can lead to intellectual handicap, epilepsy, autism, and renal or heart failure. An inactivating mutation in either of two tumor-suppressor genes-TSC1 and TSC2-is the cause of this syndrome, with TSC2 mutations accounting for 80-90% of all mutations. Molecular diagnosis of TSC is challenging, since TSC1 and TSC2 consist of 21 and 41 coding exons, respectively, and the mutation spectrum is very heterogeneous. Here we report a new approach for detecting mutations in TSC: a denaturing gradient gel electrophoresis (DGGE) analysis for small TSC2 mutations, a multiplex ligation-dependent probe amplification (MLPA) analysis for large deletions and duplications in TSC1 or TSC2, and a long-range PCR/sequencing-based analysis for small TSC1 mutations. When applied in this order, the three methods provide a new sensitive and time- and cost-efficient strategy for the molecular diagnosis of TSC. We analyzed 65 Danish patients who had been clinically diagnosed with TSC, and identified pathogenic mutations in 51 patients (78%). These included 36 small TSC2 mutations, four large deletions involving TSC2, and 11 small TSC1 mutations. Twenty-eight of the small mutations are novel. For the missense mutations, we established a functional assay to demonstrate that the mutations impair TSC2 protein function. In conclusion, the strategy presented may greatly help small- and medium-sized laboratories in the pre- and postnatal molecular diagnosis of TSC.

Impaired synaptic plasticity in a rat model of tuberous sclerosis

Tuberous sclerosis complex (TSC) is a common hereditary disorder caused by mutations in either the TSC1 or TSC2 genes, and characterized by severe epilepsy, cerebral hamartomas and mental retardation. We have used rats that are heterozygous for an autosomal-dominant germline mutation in the TSC2 gene (TSC2+/- rats) to examine the consequences of TSC2 mutations for hippocampal synaptic plasticity. While basal synaptic transmission in the Schaffer collateral-CA1 synapse was not altered, paired-pulse plasticity was significantly enhanced in TSC2+/- rats (interpulse intervals 20-200 ms). Moreover, TSC2+/- rats exhibited a marked reduction of different forms of synaptic plasticity. Long-term potentiation (LTP) elicited following high-frequency tetanization of Schaffer collaterals was significantly decreased from 1.45 +/- 0.05-fold potentiation to 1.15 +/- 0.04 (measured after 60 min). This difference in LTP levels between TSC2+/- and wild-type rats also persisted in the presence of the gamma-aminobutyric acid (GABA)(A) receptor antagonist bicuculline. In addition to changed LTP, the level of long-term depression (LTD) elicited by different forms of low-frequency stimulation was significantly less in TSC2+/- rats. These results suggest that TSC2 mutations may cause hippocampal synapses to lose much of their potential for activity-dependent synaptic modification. An understanding of the underlying molecular pathways may suggest new therapeutic approaches aimed at inhibiting the development of the profound mental retardation in TSC.

[Bilateral angiomyolipoma of the kidney in patient with tuberous sclerosis]

Angiomyolipomas are relatively frequent tumours of the kidney. It is believed that about 10 million people worldwide have such a tumour. About 1/10 of these 10 million are patients who suffer from tuberous sclerosis. The tumours are frequently bilateral, slow growing, and usually asymptomatic, as well as being rare in children. Due to the benign nature of angiomyolipomas, surgical treatment and embolisation of the tumours are generally not recommended, unless renal function is endangered, the symptoms are severe, or the kidney in question becomes completely dysfunctional. This is particularly the case in patients with tuberous sclerosis in whom these tumours are either already bilateral or may become so. We present a 24-year-old woman with tuberous sclerosis in whom bilateral kidney tumours were diagnosed 7 years earlier and in whom we carried out a left nephrectomy of a 5300 gram angiomyolipoma, which caused pain and complete loss of function. Although tumourous, the right kidney was functional, so it was left untouched. After an uneventful recovery, a close follow-up was recommended, as well as HLA typing, as it is highly probable that the right kidney will gradually become inadequate or completely dysfunctional, so that haemodialysis and/or kidney transplantation along with nephrectomy will become necessary.

Molecular neuropathology of epilepsy-associated glioneuronal malformations

Glioneuronal malformations (malformations of cortical development [MCD]) include focal cortical dysplasias (FCD) as well as highly differentiated glioneuronal tumors (i.e. gangliogliomas) and constitute frequent findings in patients with pharmacoresistent focal epilepsies. Tailored resection strategies evolved as promising treatment options and allow a systematic neuropathologic and molecular biologic examination of the epileptogenic area in these patients. The histopathologic appearance and immunophenotype of glioneuronal lesions are, however, characterized by numerous similarities and suggest impaired proliferation, migration, and differentiation of neural precursor cells to play a pathogenetic role. Recent studies point toward molecular alterations within a variety of genes and pathways involved in development of the central nervous system, neuronal growth, and maturation. Compromised signaling within insulin- or reelin-transduction cascades are common findings and were associated with specific MCD entities. Unraveling pathogenic mechanisms may advance refined classification systems for epilepsy-associated malformations and open new avenues for the development of targeted treatment strategies in pharmacoresistent focal epilepsies associated with cortical malformations.

Study of the relationship between tuberous sclerosis complex and autistic disorder

There has been increasing awareness that there are behavioral phenotypes in tuberous sclerosis complex with neuropsychiatric symptom complex such as autistic disorder and attention-deficit hyperactivity disorder (ADHD). However, the neurobiologic basis of autistic disorder in tuberous sclerosis complex is still unknown. We studied two cohorts of children followed up since 1986 until 2003, one cohort with tuberous sclerosis complex and another cohort with autistic disorder, to determine the incidence of autistic disorder in tuberous sclerosis complex and the incidence of tuberous sclerosis complex in autistic disorder respectively. We established a Tuberous Sclerosis Complex Registry in 1985 at the University of Hong Kong. In 2004, 44 index cases (the male to female ratio was 0.75:1) were registered. Three had a positive family history of tuberous sclerosis complex. Thus, the total number of tuberous sclerosis complex cases was 47. We adopted the diagnostic criteria of tuberous sclerosis complex for case ascertainment. The period prevalence rate of tuberous sclerosis complex for children and adolescents aged < 20 years is 3.5 per 10,000 (on Hong Kong island, excluding the eastern region with 125,100 aged < 20 years in 2003). Of 44 cases with tuberous sclerosis complex, 7 had autistic disorder. Thus, the incidence of autistic disorder in tuberous sclerosis complex is 16%. During the 17-year period (1986-2003), we collected a database of 753 children (668 boys and 84 girls; male to female ratio 8:1) with autistic disorder and pervasive developmental disorders. For all children with autistic disorder or pervasive developmental disorders, we routinely examined for any features of tuberous sclerosis complex by looking for neurocutaneous markers such as depigmented spots, which appear in 50% of children with tuberous sclerosis complex by the age of 2 years. For those with infantile spasm or epilepsy, the clinical features of tuberous sclerosis complex were monitored regularly during follow-up. Of these, seven had tuberous sclerosis complex. Thus, the incidence of tuberous sclerosis complex in autistic disorder is 0.9%. All of these children are mentally retarded, with moderate to severe grades in an intellectual assessment conducted by a clinical psychologist. Future studies should be directed toward looking at the various behavioral phenotypes in tuberous sclerosis complex and defining these with standardized criteria to look for any real association with the underlying genetic mutation of TSC1 or TSC2 gene or even the site of tubers in the brain.

Comparative analysis of MR sequences to detect structural brain lesions in tuberous sclerosis

BACKGROUND

Tuberous sclerosis (TS) is a neurocutaneous genetically inherited disease with variable penetrance characterized by dysplasias and hamartomas affecting multiple organs. MR is the imaging method of choice to demonstrate structural brain lesions in TS.

OBJECTIVE

To compare MR sequences and determine which is most useful for the demonstration of each type of brain lesion in TS patients.

MATERIALS AND METHODS

We reviewed MR scans of 18 TS patients for the presence of cortical tubers, white matter lesions (radial bands), subependymal nodules, and subependymal giant cell astrocytoma (SGCA) on the following sequences: (1) T1-weighted spin-echo (T1 SE) images before and after gadolinium (Gd) injection; (2) nonenhanced T1 SE sequence with an additional magnetization transfer contrast medium pulse on resonance (T1 SE/MTC); and (3) fluid-attenuated inversion recovery (FLAIR) sequence.

RESULTS

Cortical tubers were found in significantly (P<0.05) larger numbers and more conspicuously in FLAIR and T1 SE/MTC sequences. The T1 SE/MTC sequence was far superior to other methods in detecting white matter lesions (P<0.01). There was no significant difference between the T1 SE/MTC and T1 SE (before and after Gd injection) sequences in the detection of subependymal nodules; FLAIR sequence showed less sensitivity than the others in identifying the nodules. T1 SE sequences after Gd injection demonstrated better the limits of the SGCA.

CONCLUSION

We demonstrated the importance of appropriate MRI sequences for diagnosis of the most frequent brain lesions in TS. Our study reinforces the fact that each sequence has a particular application according to the type of TS lesion. Gd injection might be useful in detecting SGCA; however, the parameters of size and location are also important for a presumptive diagnosis of these tumors.

Tuberous sclerosis: a syndrome of incomplete tumor suppression

Tuberous sclerosis (TS) is a congenital neurocutaneous syndrome (or phacomatosis) characterized by widespread development of hamartomas in multiple organs. For affected individuals, neurological and psychiatric complications are the most disabling and lethal features. Although the clinical phenotype of TS is complex, only three lesions characterize the neuropathological features of the disease: cortical tubers, subependymal nodules, and subependymal giant cell astrocytomas. The latter is a benign brain tumor of mixed neuronal and glial origin. Tuberous sclerosis is caused by loss-of-function mutations in one of two genes, TSC1 or TSC2. The normal cellular proteins encoded by these genes, hamartin and tuberin, respectively, form a heterodimer that suppresses cell growth in the central nervous system by dampening the phosphatidylinositol 3–kinase signal transduction pathway. The authors review the clinical and neuropathological features of TS as well as recent research into the molecular biology of this disease. Through this work, investigators are beginning to resolve the paradoxical findings that malignant cancers seldom arise in patients with TS, even though the signaling molecules involved are key mediators of cancer cell growth.

Neurocutaneous syndromes: behavioral features

Neurocutaneous syndromes are disorders characterized by a neurological abnormality and cutaneous manifestations. Three of the more common neurocutaneous syndromes are Sturge-Weber syndrome, tuberous sclerosis, and neurofibromatosis. This review focuses on the cognitive and behavioral features of these syndromes.

Distinct Allelic Variants of TSC1 and TSC2 in Epilepsy-Associated Cortical Malformations Without Balloon Cells

Epilepsy-associated malformations of cortical development (MCDs) comprise a variety of dysplastic and neoplastic lesions of yet undetermined molecular pathology. Histopathologic similarities between MCDs and dysplastic brain lesions in the autosomal inherited neurocutaneous phacomatosis tuberous sclerosis (TSC), which affects the TSC1 and/or TSC2 genes, suggest common pathogenetic mechanisms. Previous studies revealed different alterations of TSC1 and TSC2 in epilepsy-associated malformations and glio-neuronal tumors despite histopathologic similarities. In order to examine current clinico-pathologic classification systems of cortical malformations on the molecular level, we carried out a mutational analysis of TSC1 and TSC2 in a series of surgical specimens obtained from patients with FCD without Taylor type balloon cells (FCDIIa; n = 20), architectural dysplasias (FCDI; n = 15), nodular cortical heterotopias (NCH; n = 4), and heterotopic white matter neurons (WMNH; n = 19). In FCDIIa, abundant genomic polymorphisms were detected in TSC2 (intron 4) but no allelic variants observed in exon 17 of TSC1. This allelic distribution pattern is in contrast to findings in FCDI and WMNH but also to those previously reported in FCDIIb (Taylor's balloon cell type). The latter revealed increased frequencies of specific alleles only in TSC1. The determination of characteristic molecular genetic alterations in specific epilepsy-associated malformations will support a comprehensive clinico-pathologic classification system and help to identify molecular pathways with potential pathogenetic relevance. Our work is supported by DFG (SFB TR3 [AJB], DFG Bl 421/1-1 [IB]), BONFOR, and Deutsche Krebshilfe.

Molecular genetic basis of tuberous sclerosis complex: from bench to bedside

Tuberous sclerosis complex is an autosomal dominant disease of benign tumors occurring in multiple organ systems of the body. Either of two genes, TSC1 or TSC2, can be mutated, resulting in the tuberous sclerosis complex phenotype. The protein products of the tuberous sclerosis complex genes, hamartin (TSC1) and tuberin (TSC2), have been discovered to play important roles in several cell-signaling pathways. Knowledge regarding the function of the tuberin-hamartin complex has led to therapeutic intervention trials. Numerous pathogenic mutations have been elucidated in individuals affected with tuberous sclerosis complex. Information on the type and distribution of nearly 1000 mutations in the two genes is discussed. Mosaicism for tuberous sclerosis complex mutations has been documented, complicating provision of genetic counseling to families. Emerging genotype-phenotype correlations should provide guidance for better medical care of individuals with tuberous sclerosis complex.

Behavioral and cognitive aspects of tuberous sclerosis complex

Tuberous sclerosis complex is a multisystem genetic disorder. Of all the possible manifestations of this complex disorder, the cognitive and behavioral problems represent the area of greatest concern to parents and caregivers. This review outlines the current evidence regarding global intellectual abilities, behavioral problems, psychiatric diagnoses, learning disorders, and specific neuropsychologic deficits for which individuals with tuberous sclerosis complex are at particularly increased risk, and outlines approaches to intervention. Approximately half of individuals diagnosed with tuberous sclerosis complex present with global intellectual impairment and developmental psychopathologies. Those with normal intellectual abilities are also at high risk of specific neuropsychologic deficits and behavioral, learning, and other psychiatric disorders. There is no evidence for an inevitable decline in cognition or behavior, and any such changes should be investigated. The evolving neurocognitive literature suggests that frontal brain systems might be most consistently disrupted by tuberous sclerosis complex-related neuropathology, thus leading to abnormalities in regulatory and goal-directed behaviors.

Coordinate regulation of translation by the PI 3-kinase and mTOR pathways

Control of translation initiation is an important means by which cells tightly regulate the critical processes of growth and proliferation. Multiple effector proteins contribute to translation initiation of specially modified mRNAs that modulate these processes. Coordinated regulation of these translational effectors by multiple signaling pathways allows the integration of information regarding mitogenic signals, energy levels, and nutrient sufficiency. The mTOR protein, in particular, serves as a sensor of all of these signals and is thought to thus serve as a crucial checkpoint control protein. Signals from the mTOR pathway converge with mitogenic inputs from the phosphoinositide (PI) 3-kinase pathway on translational effector proteins to coordinately control cellular growth, size, and cell proliferation. The translational effectors regulated by the PI 3-kinase and mTOR pathways and their roles in regulation of cellular growth will be the primary focus of this review.

Loss of expression of tuberin and hamartin in tuberous sclerosis complex-associated but not in sporadic angiofibromas

BACKGROUND

Angiofibromas occur sporadically, and they develop in most patients with tuberous sclerosis complex (TSC), which is associated with alterations of the tumor suppressor genes TSC1 or TSC2. Loss of tuberin, the protein product of TSC2, has been shown in the interstitial fibroblast compartment of TSC-associated angiofibromas. It is unclear whether there is also a loss of hamartin, the product of TSC1 in TSC-associated and sporadic angiofibromas.

METHODS

The expression of hamartin and tuberin was analyzed by immunohistochemistry in 59 TSC-associated and 12 sporadic angiofibromas using affinity-purified antibodies.

RESULTS

Loss of expression of both tuberin and hamartin was detected in 14 angiofibromas, loss of only tuberin in three, and loss of only hamartin in four TSC-associated angiofibromas; but there was no loss in the sporadic angiofibromas. Only the interstitial cells, but not the vascular cells, showed a loss of expression of tuberin or hamartin.

CONCLUSIONS

Loss of tuberin or hamartin occurred in a minority of the TSC-linked angiofibromas, but not in the sporadic angiofibromas. The absence of both tuberin and hamartin in some of the tumors suggests that the stability of tuberin and hamartin, which are believed to form an active complex in vivo, is negatively affected by the absence of either of the partners.

Pulmonary lymphangioleiomyomatosis: a case report with immunohistochemical details and DNA analysis

A 47-year-old woman is presented with pulmonary lymphangioleiomyomatosis (PLAM) involving the bilateral lung and slight pulmonary function abnormality. Computed tomography scan showed bilateral microcyst formation in the lung. Histologically, proliferating spindle shaped cells with centrilobular emphysema were main findings. Immunohistochemically, these proliferating spindle shaped cells were positive for alpha-smooth muscle actin, desmin, vimentin, HMB45, estrogen receptor and progesterone receptor, but negative for S-100, cytokeratin. Single strand conformation polymorphism (SSCP) and DNA analysis for tuberous sclerosis 1 and 2 showed no significant abnormality.

Tuberous sclerosis as an underlying basis for infantile spasm

The study of the molecular pathogenesis of epilepsy in tuberous sclerosis has taken on a new dimension with the identification of the TSC1 and TSC2 genes. While the development of seizures is ultimately related to mutations in one of the two genes, the mechanism underlying the genotype-phenotype relationship remains a puzzle. This chapter, presented arguments in favor of the hypothesis that abnormal cortical excitability originates in and around focal areas of structural malformations (i.e., cortical tubers and dysplasia) and that these "lesions" are the biologic consequences of tuberin and/or hamartin dysfunction. This model relies on the concept of a multistep process occurring early in cortical development whereby certain progenitor cells in the germinal layer of the ventricular zone destined for the cortex undergo inactivation of the TSC1 or TSC2 locus (Fig. 2). Immature neuroepithelial cells carrying "two-hit" mutations at either locus are believed to proliferate, migrate, and differentiate abnormally, resulting in the formation of "dysplastic" cells that are heterotopic in distribution. The pathology of the classic tuber suggests a clonal expansion of the bizarre-appearing giant cells that display incomplete, multilineage, and often ambiguous phenotype. Further, they infiltrate the six-layered structure of the cortex to form a poorly circumscribed area containing a mixture of cell types to create a highly disorganized region of a neuronal and glial network. Whether arising from the dysplastic "two-hit" target cells themselves or adjacent "innocent" bystander neurons as a result of aberrant cell-cell interaction, abnormal epileptic discharges originate from these structural abnormalities. The mechanism of how TSC1 and TSC2 inactivation causes tuber to develop is not known, but emerging experimental evidence suggests a disruption of the hamartin-tuberin "haloenzyme" in the regulation of cell size and number via the insulin signaling pathway and a p27/CDK-dependent mechanism. Biochemically, TSC1/TSC2 may associate with cytoskeletal components and vesicular adaptors in regulating sorting and trafficking of newly synthesized and recycling proteins in the post-Golgi compartments. As such, spatial and temporal localization of proteins may be affected in tuberin or hamartin-deficient neuronal cells where proper synaptic delivery of neurotransmitters plays an important role in normal cerebral function. We are in the earliest stages of understanding the role of TSC genes in epileptogenesis. To test the hypothesis outlined earlier, there is a need to create in vitro and in vivo models, as direct human experimentation is not feasible. To date, there are several rodent models of TSC, both spontaneous and recombinant strains. Unfortunately, none has consistently developed spontaneous cortical tubers, although one example was reported in an otherwise asymptomatic Eker rat (Mizuguchi et al., 2000). If the "two-hit" hypothesis is operational in tubers, as seen in other TSC lesions, it follows that radiation and chemical carcinogens should have a quantitative and qualitative effect on the development of these cerebral malformations. In preliminary experiments, we have found evidence of areas of cortical dysplasia in Eker rats irradiated early in life (Fig. 3). These dysplastic [figure: see text] cells stained positively with NeuN, consistent with the immunophenotype of cells in tubers. Alternatively, one can analyze the in vivo and in vitro characteristics of neuroprogenitor cells that are deficient of hamartin or tuberin. While homozygous mutants of TSC1 and TSC2 are lethal during midgestation, one of several techniques can be used to derive mutant neuroepithelial cells, including the procurement of -/- cells prior to embryonic deaths and subsequent cortical transplantation into syngeneic animals, development of conditional "knock outs," or chimeric mutants. These approaches, with their unique advantages and disadvantages, will be helpful in gaining insights into the development of cortical tubers and their electrophysiologic consequences.

Neurocutaneous disorders

"Neurocutaneous disorders" is a catch-all phrase that includes all disorders involving both the nervous systems and the skin. These may range from disorders in which cutaneous findings are essential to diagnosis to those with less significant involvement of the skin. Because of the variety of disorders that involve the skin and the nervous system, this article reviews a few of the more essential diagnoses, and those with recent advancements in diagnosis and management. Many of these diseases are single gene disorders, for which the genes have been discovered in the past few years. The article is divided into sections, highlighting disorders transmitted by different inheritance pattern.

Focal cortical dysplasia of Taylor's balloon cell type: mutational analysis of the TSC1 gene indicates a pathogenic relationship to tuberous sclerosis

Focal cortical dysplasia (FCD) is characterized by a localized malformation of the neocortex and underlying white matter. Balloon cells, similar to those observed in tuberous sclerosis, are present in many cases (FCD(bc)). In these patients, a hyperintense funnel-shaped subcortical lesion tapering toward the lateral ventricle was the characteristic finding on fluid-attenuated inversion recovery magnetic resonance imaging scans. Surgical lesionectomy results in complete seizure relief. Although the pathogenesis of FCD(bc) remains uncertain, histopathological similarities indicate that FCD(bc) may be related pathogenetically to tuberous sclerosis. Here, we studied alterations of the TSC1 and TSC2 genes in a cohort of patients with chronic, focal epilepsy and histologically documented FCD(bc) (n = 48). DNA was obtained after microdissection and laser-assisted isolation of balloon cells, dysplastic neurons, and nonlesional cells from adjacent normal brain tissue. Sequence alterations resulting in amino acid exchange of the TSC1 gene product affecting exons 5 and 17 and silent base exchanges in exons 14 and 22 were increased in patients with FCD(bc) compared with 200 control individuals (exon 5, 2.3% FCD(bc) vs 0% C; exon 17, 35% FCD(bc) vs 1.0% C; exon 14, 37.8% FCD(bc) vs 15% C; exon 22, 45% FCD(bc) vs 23.8% C). Sequence alterations could be detected in FCD(bc) and in adjacent normal cells. In 24 patients, DNA was suitable to study loss of heterozygosity at the TSC1 gene locus in microdissected FCD(bc) samples compared with control tissue. Eleven FCD(bc) cases exhibited loss of heterozygosity. In the TSC2 gene, only silent polymorphisms were detected at similar frequencies as in controls. Our findings indicate that FCD(bc) constitutes a clinicopathological entity with distinct neuroradiological, neuropathological, and molecular genetic features. These data also suggest a role of the TSC1 gene in the development of FCD(bc) and point toward a pathogenic relationship between FCD(bc) and the tuberous sclerosis complex.

Identification of loci associated with putative recurrence genes in transitional cell carcinoma of the urinary bladder

Following an earlier study linking monosomy 9 with recurrence of transitional cell carcinomas (TCCs) of the urinary bladder, 109 primary and recurrent TCCs (from 47 patients) were examined to explore genetic alterations at chromosome 9 associated with recurrence. Patient DNA was microdissected and extracted from archival tissue sections and analysed for loss of heterozygosity (LOH) at three regions on chromosome 9 where tumour suppressor genes (TSGs) are known to reside (INK 4A, DBC1, and TSC1). Patients were categorized into two groups, non-recurrent TCC (NR, n=18) and recurrent TCC (REC, n=29). It was noted that 12% of NR tumours, compared with 54% of REC primary tumours (p=0.01), had LOH at all informative markers spanning the TSC1 region. The risk of recurrence was significantly higher in patients with deleted TSC1 than in those who retained the TSC1 region (p=0.035). Levels of LOH at DBC1 or INK 4A were not significantly different in NR tumours than in REC primary tumours and recurrence-free survival was not affected by loss of either of these genes. Loss of all informative markers spanning chromosome 9 was observed in 0% of NR tumours compared with 25% of REC primary tumours (p=0.04). The probability of recurrence was also significantly increased in patients who had LOH at all informative markers spanning chromosome 9 (p=0.016), confirming earlier fluorescence in situ hybridization results. This study provides further evidence that recurrence in bladder cancer is a distinct event, with underlying molecular causes. It also identifies the TSC1 locus as a candidate for a TSG, which drives recurrence in a proportion of TCC patients. Loss of all informative markers, including those residing in the TSC1 region, spanning chromosome 9 was also linked to recurrence.

Neurologic manifestations of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a multiorgan disorder that primarily affects the brain, skin, and kidneys. Recent advances have elucidated the genetics of this complex, which has helped lead to an increased understanding of the basic neurobiology of this disorder. There is both phenotypic and geneotypic heterogeneity. The treatment of epilepsy remains a major challenge in these patients, and there is an increasing role for epileptic surgery. Many patients with TSC continue to have intractable seizures. Early identification to ensure proper monitoring and genetic counseling continue to be important clinically. The neurologist must be aware of other organ involvement, particularly the kidneys, and the lungs in female patients, to ensure appropriate monitoring for complications. It is also important to be aware of the marked variability of expression in all the clinical features of TSC.

Evidence for separable functions of tuberous sclerosis gene products in mammalian cell cycle regulation

Tuberous sclerosis is an autosomal dominant disease affecting approximately 1 in 6,000 individuals. It is caused by mutations in either TSC1 on chromosome 9q34, which encodes hamartin, or TSC2 on chromosome 16p13.3, which encodes tuberin. The growths, named hamartomas, characteristically occur in different organs of patients and are speculated to result from defects in proliferation control. The observation that hamartin and tuberin can interact in vivo suggests that they might function in the same complex. Here we show that hamartin can affect proliferation control independent of the presence of functional tuberin and that binding to hamartin is not essential for tuberin to affect proliferation. Ectopic expression of hamartin negatively regulates proliferation to a similar extent in tuberin-positive and tuberin-negative cells; this is accompanied by binding to tuberin and upregulation of endogenous p27 in tuberin-positive cells and is without effects on p27 expression in the latter. Our data show for the first time that TSC proteins possess separable functions. We further demonstrate that hamartin can deregulate proliferation control by different mechanisms depending on the presence of tuberin. Besides an overlap in many features of patients with TSC1 and TSC2 mutations, data has accumulated that provides evidence for specific clinical differences. This study provides new insights into the cellular roles of TSC proteins and initiates a discussion of whether separable functions of these proteins might be associated with the clinical differences of TSC1- and TSC2-associated disease.

Analysis of the TSC1 and TSC2 genes in sporadic renal cell carcinomas

The genetic events involved in the aetiology of non-clear-cell renal cell carcinoma (RCC) and a proportion of clear cell RCC remain to be defined. Germline mutations of the TSC1 and TSC2 genes cause tuberous sclerosis (TSC), a multi-system hamartoma syndrome that is also associated with RCC. We assessed 17 sporadic clear cell RCCs with a previously identified VHL mutation, 15 clear-cell RCCs without an identified VHL mutation and 15 non-clear-cell RCCs for loss of heterozygosity (LOH) at chromosomes 9q34 and 16p13.3, the chromosomal locations of TSC1 and TSC2. LOH was detected in 4/9, 1/11 and 3/13 cases informative at both loci. SSCP analysis of the whole coding region of the retained allele did not reveal any cases with a detectable intragenic second somatic mutation. Furthermore, RT-PCR analysis of TSC1 and TSC2 on total RNA from 8 clear-cell RCC cell lines confirmed expression of both TSC genes. These data indicate that biallelic inactivation of TSC1 or TSC2 is not frequent in sporadic RCC and suggests that the molecular mechanisms of renal carcinogenesis in TSC are likely to be distinct.

Drosophila Tsc1 Functions with Tsc2 to Antagonize Insulin Signaling in Regulating Cell Growth, Cell Proliferation, and Organ Size

Tuberous sclerosis complex is a dominant disorder that leads to the development of benign tumors in multiple organs. We have isolated a mutation in the Drosophila homolog of TSC1 (Tsc1). Cells mutant for Tsc1 are dramatically increased in size yet differentiate normally. Organ size is also increased in tissues that contain a majority of mutant cells. Clones of Tsc1 mutant cells in the imaginal discs undergo additional divisions but retain normal ploidy. We also show that the Tsc1 protein binds to Drosophila Tsc2 in vitro. Overexpression of Tsc1 or Tsc2 alone in the wing and eye has no effect, but co-overexpression leads to a decrease in cell size, cell number, and organ size. Genetic epistasis data are consistent with a model that Tsc1 and Tsc2 function together in the insulin signaling pathway.

Denaturing high-performance liquid chromatography (DHPLC)-based prenatal diagnosis for tuberous sclerosis

Tuberous sclerosis (TSC) is a frequent autosomal-dominant condition (affecting 1 in 6000 individuals) caused by various mutations in either the hamartin (TSC1) or the tuberin gene (TSC2). This allelic and non-allelic heterogeneity makes genetic counseling and prenatal diagnosis difficult, especially as a significant proportion of TSC cases are due to de novo mutations. For this reason the identification of the disease causing mutation is mandatory for accurate counseling, yet current mutation detection methods such as single-strand conformation polymorphism (SSCP) or denaturing gradient gel electrophoresis (DGGE) are labor intensive with limited detection efficiency. Denaturing high-performance liquid chromatography (DHPLC) is a high-throughput, semi-automated mutation detection system with a reported mutation detection rate close to 100% for PCR fragments of up to 800 bp. We used a recently described DHPLC assay allowing the efficient detection of mutations in TSC1 to analyze the DNA extracted from a chorion villus sample in order to perform a prenatal diagnosis for TSC. The fetus was found not to have inherited the deleterious mutation and the DHPLC diagnosis was confirmed by haplotype analysis. This represents the first DHPLC-based prenatal diagnosis of a genetic disease.

Mutational analysis of TSC1 and TSC2 genes in gangliogliomas

Gangliogliomas constitute the most frequent tumour entity in patients with temporal lobe epilepsy. The characteristic histopathological admixture of glial and neuronal elements, the focal nature and their differentiated phenotype and benign biological behaviour suggest an origin from a developmentally compromised or dysplastic precursor lesion. The present study analysed TSC1 and TSC2 genes as potential candidates involved in the pathogenesis of this intriguing neoplasm. Recent data suggest that both genes play a role in cortical differentiation and growth control. DNA sequence analysis of TSC1 and TSC2 was studied in 20 patients with gangliogliomas. Fifteen of these tumours (75%) carried polymorphisms in the TSC2 gene. The frequency of these polymorphisms was significantly increased in intron 4 (12.5%) and exon 41 (15%) compared to control individuals (8.1 and 6.5%, respectively, n = 100). A somatic mutation in intron 32 of the TSC2 gene was encountered in one patient. In the TSC1 gene, seven polymorphisms occurred as a combination of base exchanges in exon 14 and intron 13. No mutations were observed in this gene. Laser microdissection and harvesting of individual neuronal and glial elements identified the intron 32 mutation within the glial portion but not in dysplastic neurones of the tumour. The data demonstrate numerous polymorphisms as well as a novel TSC2 mutation in gangliogliomas from patients with chronic epilepsies. The selective detection of the TSC2 mutation within the glial component of a ganglioglioma suggests that the glioma portion has undergone clonal evolution in this case.

Mutational analysis in a cohort of 224 tuberous sclerosis patients indicates increased severity of TSC2, compared with TSC1, disease in multiple organs

Tuberous sclerosis (TSC) is a relatively common hamartoma syndrome caused by mutations in either of two genes, TSC1 and TSC2. Here we report comprehensive mutation analysis in 224 index patients with TSC and correlate mutation findings with clinical features. Denaturing high-performance liquid chromatography, long-range polymerase chain reaction (PCR), and quantitative PCR were used for mutation detection. Mutations were identified in 186 (83%) of 224 of cases, comprising 138 small TSC2 mutations, 20 large TSC2 mutations, and 28 small TSC1 mutations. A standardized clinical assessment instrument covering 16 TSC manifestations was used. Sporadic patients with TSC1 mutations had, on average, milder disease in comparison with patients with TSC2 mutations, despite being of similar age. They had a lower frequency of seizures and moderate-to-severe mental retardation, fewer subependymal nodules and cortical tubers, less-severe kidney involvement, no retinal hamartomas, and less-severe facial angiofibroma. Patients in whom no mutation was found also had disease that was milder, on average, than that in patients with TSC2 mutations and was somewhat distinct from patients with TSC1 mutations. Although there was overlap in the spectrum of many clinical features of patients with TSC1 versus TSC2 mutations, some features (grade 2-4 kidney cysts or angiomyolipomas, forehead plaques, retinal hamartomas, and liver angiomyolipomas) were very rare or not seen at all in TSC1 patients. Thus both germline and somatic mutations appear to be less common in TSC1 than in TSC2. The reduced severity of disease in patients without defined mutations suggests that many of these patients are mosaic for a TSC2 mutation and/or have TSC because of mutations in an as-yet-unidentified locus with a relatively mild clinical phenotype.

Three novel types of splicing aberrations in the tuberous sclerosis TSC2 gene caused by mutations apart from splice consensus sequences

Disease causing aberrations in both tuberous sclerosis predisposing genes, TSC1 and TSC2, comprise nearly every type of alteration with a predominance of small truncating mutations distributed over both genes. We performed an RNA based screening of the entire coding regions of both TSC genes applying the protein truncation test (PTT) and identified a high proportion of unusual splicing abnormalities affecting the TSC2 gene. Two cases exhibited different splice acceptor mutations in intron 9 (IVS9-15G-->A and IVS9-3C-->G) both accompanied by exon 10 skipping and simultaneous usage of a cryptic splice acceptor in exon 10. Another splice acceptor mutation (IVS38-18A-->G) destroyed the putative polypyrimidine structure in intron 38 and resulted in simultaneous intron retention and usage of a downstream cryptic splice acceptor in exon 39. Another patient bore a C-->T transition in intron 8 (IVS8+281C-->T) activating a splice donor site and resulting in the inclusion of a newly recognised exon in the mRNA followed by a premature stop. These splice variants deduced from experimental results are additionally supported by RNA secondary structure analysis based on free energy minimisation. Three of the reported splicing anomalies are due to sequence changes remote from exon/intron boundaries, described for the first time in TSC. These findings highlight the significance of investigating intronic changes and their consequences on the mRNA level as disease causing mutations in TSC.

Mutation analysis of the hamartin gene using denaturing high performance liquid chromatography

Denaturing high performance liquid chromatography (DHPLC) is a novel high-capacity technique for gene mutation scanning. We have assessed the sensitivity and specificity of this method for analysis of the full coding sequence of the hamartin (TSC1) gene in 20 tuberous sclerosis patients, whose TSC1 genes previously had been studied by single strand conformation polymorphism analysis and protein truncation assay. All eight sequence variants previously identified were adequately detected by DHPLC. Additionally, this approach picked up three polymorphisms, one of which (IVS13-55 C>G) was hitherto unreported, therefore serving as proof of principle for this technique. Thus, DHPLC appears to be a highly sensitive method with advantages in terms of flexibility, fragments size analysis, cost and time and labor sparing, compared to classical approaches of mutation scanning.

Molecular genetics in pediatric dermatology

The field of pediatric dermatology continues to be enriched by the insights offered through molecular genetics. For some genetic skin disorders, including neurofibromatosis, tuberous sclerosis complex, and several forms of epidermolysis bullosa, genetic research has resulted in an evolving understanding of the relationship between genotype and phenotype, with the ability to predict some of the features of these disorders on the basis of the genetic defect. However, widespread use of molecular genetics for diagnostic testing of these disorders has not been possible because of genetic heterogeneity, limited availability, and reduced sensitivity. The appropriate use of genetic services is emphasized in this, the molecular era.

Exon scanning of the entire TSC2 gene for germline mutations in 40 unrelated patients with tuberous sclerosis

Tuberous sclerosis complex (TSC) is a dominantly inherited multisystem disorder resulting in the development of hamartomatous growths in many organs. Genetic heterogeneity has been demonstrated linking the familial cases to either TSC1 at 9q34.3, or TSC2 at 16p13.3. About two-thirds of the TSC cases are sporadic and appear to represent new mutations. While both genes are thought to account for all familial cases, with each representing approximately 50% of the mutations, the proportion of sporadic cases with mutations in TSC1 and TSC2 is yet to be determined. We have examined the entire coding sequence of the TSC2 gene in 20 familial and 20 sporadic cases and identified a total of twenty-one mutations representing 50% and 55% of familial and sporadic cases respectively. Our rate of mutation detection is significantly higher than other published reports. Twenty out of 21 mutations are novel and include 6 missense, 6 nonsense, 5 frameshifts, 2 splice alterations, a 34 bp deletion resulting in abnormal splicing, and an 18 bp deletion which maintains the reading frame. The mutations are distributed throughout the coding sequence with no specific hot spots. There is no apparent correlation between mutation type and clinical severity of the disease. Our results document that at least 50% of sporadic cases arise from mutations in the TSC2 gene. The location of the mutations described here, particularly the missense events, should be valuable for further functional analysis of this tumor suppressor protein.

The TSC1 tumour suppressor hamartin regulates cell adhesion through ERM proteins and the GTPase Rho

Loss of the tumour-suppressor gene TSC1 is responsible for hamartoma development in tuberous sclerosis complex (TSC), which renders several organs susceptible to benign tumours. Hamartin, the protein encoded by TSC1, contains a coiled-coil domain and is expressed in most adult tissues, although its function is unknown. Here we show that hamartin interacts with the ezrin-radixin-moesin (ERM) family of actin-binding proteins. Inhibition of hamartin function in cells containing focal adhesions results in loss of adhesion to the cell substrate, whereas overexpression of hamartin in cells lacking focal adhesions results in activation of the small GTP-binding protein Rho, assembly of actin stress fibres and formation of focal adhesions. Interaction of endogenous hamartin with ERM-family proteins is required for activation of Rho by serum or by lysophosphatidic acid (LPA). Our data indicate that disruption of adhesion to the cell matrix through loss of hamartin may initiate the development of TSC hamartomas and that a Rho-mediated signalling pathway regulating cell adhesion may constitute a rate-limiting step in tumour formation.

Tuberous sclerosis complex

Tuberous sclerosis complex is an autosomal dominant disorder that causes significant complications in multiple organ systems. Both basic science and clinical research on tuberous sclerosis complex have flourished in recent years, improving our understanding of its molecular genetics and pathophysiology. Two tuberous sclerosis complex genes cause nearly identical phenotypes, and great progress has been made towards understanding how each of these genes functions. The recognition of tuberous sclerosis complex improved with revised diagnostic criteria, and the management of many of the complications of tuberous sclerosis complex has improved.

Characterization of the cytosolic tuberin-hamartin complex. Tuberin is a cytosolic chaperone for hamartin

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by a broad phenotypic spectrum that includes seizures, mental retardation, renal dysfunction and dermatological abnormalities. Mutations to either the TSC1 or TSC2 gene are responsible for the disease. The TSC1 gene encodes hamartin, a 130-kDa protein without significant homology to other known mammalian proteins. Analysis of the amino acid sequence of tuberin, the 200-kDa product of the TSC2 gene, identified a region with limited homology to GTPase-activating proteins. Previously, we demonstrated direct binding between tuberin and hamartin. Here we investigate this interaction in more detail. We show that the complex is predominantly cytosolic and may contain additional, as yet uncharacterized components alongside tuberin and hamartin. Furthermore, because oligomerization of the hamartin carboxyl-terminal coiled coil domain was inhibited by the presence of tuberin, we propose that tuberin acts as a chaperone, preventing hamartin self-aggregation.

The screening and diagnosis of autistic spectrum disorders

The Child Neurology Society and American Academy of Neurology recently proposed to formulate Practice Parameters for the Diagnosis and Evaluation of Autism for their memberships. This endeavor was expanded to include representatives from nine professional organizations and four parent organizations, with liaisons from the National Institutes of Health. This document was written by this multidisciplinary Consensus Panel after systematic analysis of over 2,500 relevant scientific articles in the literature. The Panel concluded that appropriate diagnosis of autism requires a dual-level approach: (a) routine developmental surveillance, and (b) diagnosis and evaluation of autism. Specific detailed recommendations for each level have been established in this document, which are intended to improve the rate of early suspicion and diagnosis of, and therefore early intervention for, autism.

Tumor suppressor genes in ophthalmology

Tumor suppressor genes have a diversity of functions, but they have in common the property of inhibiting neoplastic transformation. When they become inactivated, a constraint is removed that allows cells to grow inappropriately. Mutations in these genes are now thought to be the initiating events in most cancers. The first tumor suppressor gene was discovered through its role in retinoblastoma, and many other tumor suppressor genes also have important ophthalmic manifestations. The first group of tumor suppressor genes to be discussed are those involved in retinoblastoma and uveal melanoma. These are among the most frequently mutated genes in human cancer and are key regulators of growth and homeostasis. The second group of genes is associated with specific hereditary tumor syndromes with ophthalmic manifestations. These genes function in a variety of molecular pathways and are associated with neoplastic and non-neoplastic abnormalities in restricted tissue distributions. Research on tumor suppressor genes continues to shed light on the molecular pathophysiology of ophthalmic tumors and will increasingly yield diagnostic and therapeutic applications.

Protein truncation test for screening hamartin gene mutations and report of new disease-causing mutations

Considering the prevalence of truncating mutations in the tuberous sclerosis (TSC) hamartin gene (TSC1), we devised a protein truncation test (PTT) to analyze the full length coding sequence of TSC1. Studying 12 sporadic cases and three familial forms by a combination of PTT and single-strand conformation polymorphism analysis (SSCA), we found 5/15 mutations while PTT alone detected 4/15 truncating mutations, two of which escaped SSCA analysis. SSCA alone picked up one missense mutation and two mutations also detected by PTT. Interestingly, a TSC1 mutation was identified in all three familial forms (3/3) while the rate of mutation detection was lower in sporadic cases (2/12). In conclusion, PTT proves to be a useful technique for the rapid detection of disease-causing mutations in the TSC1 gene.

Analysis of both TSC1 and TSC2 for germline mutations in 126 unrelated patients with tuberous sclerosis

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by the development of multiple hamartomas involving many organs. About two-thirds of the cases are sporadic and appear to represent new mutations. With the cloning of two causative genes, TSC1 and TSC2 it is now possible to analyze both genes in TSC patients and identify germline mutations. Here we report the mutational analysis of the entire coding region of both TSC1 and TSC2 genes in 126 unrelated TSC patients, including 40 familial and 86 sporadic cases, by single-stranded conformational polymorphism (SSCP) analysis followed by direct sequencing. Mutations were identified in a total of 74 (59%) cases, including 16 TSC1 mutations (5 sporadic and 11 familial cases) and 58 TSC2 mutations (42 sporadic and 16 familial cases). Overall, significantly more TSC2 mutations were found in our population, with a relatively equal distribution of mutations between TSC1 and TSC2 among the familial cases, but a marked underrepresentation of TSC1 mutations among the sporadic cases (P = 0.0035, Fisher's exact test). All TSC1 mutations were predicted to be protein truncating. However, in TSC2 13 missense mutations were found, five clustering in the GAP-related domain and three others occurring in exon 16. Upon comparison of clinical manifestations, including the incidence of intellectual disability, we could not find any observable differences between TSC1 and TSC2 patients. Our data help define the distribution and spectrum of mutations associated with the TSC loci and will be useful for both understanding the function of these genes as well as genetic counseling in patients with the disease.

Mutation screening of the entire coding regions of the TSC1 and the TSC2 gene with the protein truncation test (PTT) identifies frequent splicing defects

Mutation analyses in tuberous sclerosis (TSC) have reported a wide variety of disease-causing aberrations in the two known predisposing genes, TSC1 and TSC2 on chromosomes 9q34 and 16p13, comprising mainly small mutations distributed over the entire genes. So far, all known TSC1 mutations as well as the majority of TSC2 mutations truncate the proteins hamartin and tuberin, respectively. We describe for the first time an RNA-based screening of the entire coding regions of both TSC genes for truncating mutations applying the protein truncation test (PTT). Simultaneous investigation of both TSC genes in a group of 48 unassigned TSC patients, which were previously tested to exclude large intragenic TSC2 rearrangements, revealed aberrant migrating polypeptides resulting from truncating mutations in nine TSC1 cases and in 16 TSC2 cases while three TSC2 cases showed enlarged proteins. TSC1 mutations include two nonsense mutations, four insertions, and three splice mutations. Nineteen mutations identified in TSC2 were composed of four different nonsense mutations in five patients, one deletion, one insertion, and seven different splicing aberrations due to at least eight different mutations found in 12 patients. Additional predicted truncating mutations according to PTT without possible identification of the causative alteration allowed assignment to TSC1 in one and TSC2 in seven cases. Twelve patients without abnormalities in the PTT are assumed to harbor missense mutations, probably in TSC2. The high proportion of TSC2 splicing aberrations strengthens the importance of intronic disease-causing mutations and the application of RNA-based screening methods to confirm their consequences.

Optimal Temperature Selection for Mutation Detection by Denaturing HPLC and Comparison to Single-Stranded Conformation Polymorphism and Heteroduplex Analysis

Background: Denaturing HPLC (DHPLC) is a semi-automated method for detecting unknown DNA sequence variants. The sensitivity of the method is dependent on the temperature at which the analysis is undertaken, the selection of which is dependent on operator experience. To circumvent this, software has been developed for predicting the optimal temperature for DHPLC analysis. We examined the utility of this software.

Methods: To maximize the relevance of our data for other investigators, we have screened 42 different amplimers from CFTR, TSC1, and TSC2. The samples consisted of 103 unique sequence heterozygotes and 126 wild-type homozygous controls.

Results: At the temperature recommended by the software, 96% (99 of 103) of heterozygotes and all of the wild-type controls were correctly classified. This compares favorably with sensitivities of 85% for single-stranded conformation polymorphism and 82% for gel-based heteroduplex analyses of the same fragments.

Conclusions: Software-optimized DHPLC is a highly sensitive method for mutation detection. However, where sensitivity &gt;96% is required, our data suggest that in addition to the recommended temperature, fragments should also be run at the recommended temperature plus 2 °C.

Novel 23-base-pair duplication mutation in TSC1 exon 15 in an infant presenting with cardiac rhabdomyomas

Tuberous sclerosis (TSC) is a dominantly inherited disorder due to mutations at two gene loci, the TSC1 locus on chromosome 9q34 and the TSC2 locus on chromosome 16p13.3. The TSC2 and the TSC1 genes have now been cloned, enabling mutation analysis. We report results of mutation analysis in a sporadic case of TSC first identified in intra-uterine life on the basis of the presence of cardiac rhabdomyomas. Postnatally this infant was also found to have subependymal nodules on brain computed tomographic scan. Hypomelanotic macules were not detected neonatally or at 12 months of age. The specific TSC1 exon 15 mutation found in our patient has not previously been reported in cases of TSC. This mutation involves duplication of a 23-bp segment of DNA between two 9-bp repeated sequence elements within exon 15. These repeat elements are located between nucleotides 1892-1900 and between nucleotides 1915-1923 within the TSC1 gene sequence. It is likely that the presence of these two repeated elements predisposes to misalignment of DNA strands and unequal crossing over. The mechanism of origin of rhabdomyomas in TSC is reviewed. Loss of heterozygosity in the TSC gene regions has been reported in cardiac rhabdomyomas; however, these lesions are self-limiting in their growth. The basis for this self limiting proliferation is not clear. One interesting postulation is that cardiac rhabdomyomas may be due to delay or failure of apoptosis which occurs as part of the normal remodeling process in the heart.

Comprehensive mutation analysis of TSC1 and TSC2-and phenotypic correlations in 150 families with tuberous sclerosis

Tuberous sclerosis (TSC [MIM 191090 and MIM 191100]) is an autosomal dominant disorder characterized by hamartomas in many organs. Two thirds of cases are sporadic and are thought to represent new mutations. TSC is caused by mutations affecting either of the presumed tumor-suppressor genes, TSC1 and TSC2. Both appear to function as tumor suppressors, because somatic loss or intragenic mutation of the corresponding wild-type allele is seen in the associated hamartomas. Here we report the first comprehensive mutation analysis of TSC1 and TSC2 in a cohort of 150 unrelated TSC patients and their families, using heteroduplex and SSCP analysis of all coding exons and using pulsed-field gel electrophoresis and conventional Southern blot analysis and long PCR to screen for large rearrangements. Mutations were characterized in 120 (80%) of the 150 cases, affecting TSC1 in 22 cases and TSC2 in 98 cases. TSC1 mutations were significantly underrepresented in sporadic cases (P=. 000185). Twenty-two patients had TSC2 missense mutations that were found predominantly in the GAP-related domain (eight cases) and in a small region encoded in exons 16 and 17, between nucleotides 1849 and 1859 (eight cases), consistent with the presence of residues performing key functions at these sites. In contrast, all TSC1 mutations were predicted to be truncating, consistent with a structural or adapter role for the encoded protein. Intellectual disability was significantly more frequent in TSC2 sporadic cases than in TSC1 sporadic cases (P=.0145). These data provide the first representative picture of the distribution and spectrum of mutations across the TSC1 and TSC2 loci in clinically ascertained TSC and support a difference in severity of TSC1- and TSC2-associated disease.

Mutation of the 9q34 gene TSC1 in sporadic bladder cancer

Deletions involving chromosome 9 occur in more than 50% of human bladder cancers of all grades and stages. Most involve loss of the whole chromosome or of an entire chromosome arm but some small deletions are found which can be used to define critical regions which may contain tumour suppressor genes. We have localized such a critical region of deletion at 9q34 between the markers D9S149 and D9S66, an interval which contains the Tuberous Sclerosis gene TSC1. Single strand conformation polymorphism (SSCP) and sequence analysis of TSC1 in bladder tumours and cell lines with 9q34 loss of heterozygosity (LOH) has identified five mutations in retained TSC1 alleles. Our results support the hypothesis that TSC1 can act as a bladder tumour suppressor gene.

Mutational spectrum of the TSC1 gene in a cohort of 225 tuberous sclerosis complex patients: no evidence for genotype-phenotype correlation

Tuberous sclerosis complex is an inherited tumour suppressor syndrome, caused by a mutation in either the TSC1 or TSC2 gene. The disease is characterised by a broad phenotypic spectrum that can include seizures, mental retardation, renal dysfunction, and dermatological abnormalities. The TSC1 gene was recently identified and has 23 exons, spanning 45 kb of genomic DNA, and encoding an 8.6 kb mRNA. After screening all 21 coding exons in our collection of 225 unrelated patients, only 29 small mutations were detected, suggesting that TSC1 mutations are under-represented among TSC patients. Almost all TSC1 mutations were small changes leading to a truncated protein, except for a splice site mutation and two in frame deletions in exon 7 and exon 15. No clear difference was observed in the clinical phenotype of patients with an in frame deletion or a frameshift or nonsense mutation. We found the disease causing mutation in 13% of our unrelated set of TSC patients, with more than half of the mutations clustered in exons 15 and 17, and no obvious under-representation of mutations among sporadic cases. In conclusion, we find no support for a genotype-phenotype correlation for the group of TSC1 patients compared to the overall population of TSC patients.

Neurology and the skin

As knowledge of pathophysiology grows, so does the refinement of diagnoses. Sometimes increased knowledge permits consolidation and unification. Unfortunately, at our present level of understanding, it usually demands proliferation of diagnostic categories. As tedious as this diagnostic splintering may seem, such is the price currently exacted of both the investigator and the clinician who seek to optimise management. Increased diagnostic refinement often requires inquiry into matters outside the bounds of one's specialty. Most often we turn to the radiologist or to the laboratory to narrow the differential diagnosis generated from the history and neurological examination. As we have shown, a useful intermediate step is extension of the physical examination to organs such as the skin, which are not the traditional preserve of the neurologist. That any text could confer the sophistication required for expert dermatological diagnosis is an unrealistic expectation. However, we hope that this review will encourage careful examination of the skin, hair, and nails by the neurological practitioner, with consideration of referral to a dermatologist when greater expertise is required.

Diagnosis and management of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal-dominant neurocutaneous disorder with a high spontaneous mutation rate. Understanding of this disorder has greatly increased in recent years. Two chromosomal loci can produce the TSC phenotype: 9q34 and 16p13. These appear to code for proteins that have a tumor suppressor function. TSC results in hamartomas that affect various organ systems, most commonly brain, skin, heart, and kidney. Previously thought to consist of intractable seizures, facial angiofibromas, and dementia, increasing numbers of persons with less severe involvement have been identified. Diagnostic criteria, various types of lesions, and medical management are reviewed.