The paradox of autophagy in Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder caused by germline mutations in TSC1 or TSC2 genes, which leads to the hyperactivation of the mTORC1 pathway, an important negative regulator of autophagy. This leads to the development of hamartomas in multiple organs. The variability in symptoms presents a challenge for the development of completely effective treatments for TSC. One option is the treatment with mTORC1 inhibitors, which are targeted to block cell growth and restore autophagy. However, the therapeutic effect of rapamycin seems to be more efficient in the early stages of hamartoma development, an effect that seems to be associated with the paradoxical role of autophagy in tumor establishment. Under normal conditions, autophagy is directly inhibited by mTORC1. In situations of bioenergetics stress, mTORC1 releases the Ulk1 complex and initiates the autophagy process. In this way, autophagy promotes the survival of established tumors by supplying metabolic precursors during nutrient deprivation; paradoxically, excessive autophagy has been associated with cell death in some situations. In spite of its paradoxical role, autophagy is an alternative therapeutic strategy that could be explored in TSC. This review compiles the findings related to autophagy and the new therapeutic strategies targeting this pathway in TSC.     

Genetics and Molecular Biology of Mouse Pigmentation

The formation of mouse coat color is a relatively complex developmental process that is affected by a large number of mutations, both naturally occurring and induced. The cloning of the genes in which these mutations occur and the elucidation of the mechanisms by which these mutations disrupt the normal pigmentation pattern is leading to an understanding of the way interactions between gene products lead to a final phenotype.     

Application of Molecular Biology and Genetics in Endocrinology

ObjectiveTo review the growing impact of molecular biology and genetics on clinical endocrinology.MethodsMedical literature, databases, and Web sites describing genetics and genomic medicine with relevance for clinical endocrinology were reviewed.ResultsMany monogenic disorders can now be explained at the molecular level and the diagnosis can be established through mutational analysis. The ability to establish a molecular diagnosis is relevant for carrier detection and genetic counseling. In contrast to the significant advances in monogenic disorders, the current knowledge about the genetic components contributing to the pathogenesis of complex disorders is still relatively modest and is a major focus of current research efforts. Molecular biology already has an important impact on therapy in endocrine disorders. A broad spectrum of recombinant peptides and proteins are used in daily practice, eg, insulin and insulin analogues. Moreover, the increasingly detailed understanding of the molecular pathogenesis of cancer is leading to the development of novel and more specific inhibitors. While genetic testing has many advantages, it is important that physicians and patients are aware of potential limitations. They include, among others, technical limitations and allelic and nonallelic heterogeneity. These limitations need to be discussed in detail with patients and relatives, and it is often useful to involve a genetic counselor before obtaining informed consent by the individuals undergoing testing.ConclusionMolecular biology and genetics play an increasingly important role for the diagnosis and therapy of endocrine disorders. Challenges for the future include the elucidation of the genetic components contributing to complex disorders, eg, diabetes mellitus type 2, and the development of cheaper and comprehensive DNA sequencing technologies. Lastly, it is important that there is continuing attention directed towards the ethical, social, and legal aspects surrounding genetic medicine. (Endocr Pract, 2007;13: 534-541)     

结节性硬化症伴癫痫患儿临床特征和基因型分析

摘要 目的：探讨结节性硬化症（TSC）伴癫痫患儿的临床特征和基因型特点,旨在了解 TSC伴癫痫患儿的临床表现,以及表型与基因型的相关性,为临床诊治提供更有效的方案。方法：回顾性分析 2019年 12月至 2021年 1月安徽省儿童医院神经内科收治的 10例 TSC伴癫痫患儿的临床表现,采用芯片捕获高通量测序以及 Sanger测序验证,对 TSC伴癫痫患儿及父母进行基因检测,分析其临床及遗传变异的特征。结果：10例中男性 4例,女性 6例,首次发作痉挛 3例,局灶性 7例,70.00%首发年龄小于 1岁。临床表现：90.00%皮肤病变,80.00%心脏横纹肌瘤,20.00%眼底异常,未见肾脏、肝脏、肺脏病变。视频脑电图显示 60.00%痫样波位于额颞区,100.00%伴神经影像学皮层 /皮层下异常,90.00%双侧室管膜 /室管膜下异常,10.00%室管膜下巨细胞星形细胞瘤。研究患儿均完善基因检测,3例为 TSC1基因突变,7例为 TSC2突变,包括错义、移码及剪接位点突变,2例检测出家族变异,7例均未检测出家族变异。结论：TSC伴癫痫患儿男女发病无明显差异性,散发病例多见,发病年龄多为 1岁内,首次发作常为局灶性。视频脑电图痫样波额颞区为主,头颅影像学多为皮层 /皮层下及双侧室管膜 /室管膜下异常。TSC2突变较 TSC1突变常见,临床表现严重,痉挛发生率高,发病年龄小,多控制不佳。早期基因检测,对于发病年龄小,疗效欠佳患儿尤为重要。     

Vigabatrin Inhibits Seizures and mTOR Pathway Activation in a Mouse Model of Tuberous Sclerosis Complex

Epilepsy is a common neurological disorder and cause of significant morbidity and mortality. Although antiseizure medication is the first-line treatment for epilepsy, currently available medications are ineffective in a significant percentage of patients and have not clearly been demonstrated to have disease-specific effects for epilepsy. While seizures are usually intractable to medication in tuberous sclerosis complex (TSC), a common genetic cause of epilepsy, vigabatrin appears to have unique efficacy for epilepsy in TSC. While vigabatrin increases gamma-aminobutyric acid (GABA) levels, the precise mechanism of action of vigabatrin in TSC is not known. In this study, we investigated the effects of vigabatrin on epilepsy in a knock-out mouse model of TSC and tested the novel hypothesis that vigabatrin inhibits the mammalian target of rapamycin (mTOR) pathway, a key signaling pathway that is dysregulated in TSC. We found that vigabatrin caused a modest increase in brain GABA levels and inhibited seizures in the mouse model of TSC. Furthermore, vigabatrin partially inhibited mTOR pathway activity and glial proliferation in the knock-out mice in vivo, as well as reduced mTOR pathway activation in cultured astrocytes from both knock-out and control mice. This study identifies a potential novel mechanism of action of an antiseizure medication involving the mTOR pathway, which may account for the unique efficacy of this drug for a genetic epilepsy.     

Genetics,Molecular Biology,and Phenotypes of X-Linked Epilepsy

Epilepsy is a common and diverse set of chronic neurological disorders characterized by spontaneous, unprovoked, and recurrent epileptic seizures. Environmental factors and acquired disposition are proposed to play a role to the pathogenesis of epilepsy. Genetic factors are important contributors as well. Comparing to the phenotype of epilepsy caused by mutation of single gene on an autosome, the phenotype of X-linked epilepsy is more complex. X-linked epilepsy usually manifests as part of a syndrome or epileptic encephalopathy, and the variability of clinical manifestations of X-linked epilepsy may be attributed to several factors including the type of genetic mutation, methylation, X chromosome random inactivation, and mosaic distribution. As a result, it is difficult to establish the genotype–phenotype correlation, diagnostic tests, and genetic counseling. In this review, we provide an overview of the X-linked epilepsy including responsible loci and genes, the molecular biology, the associated complex phenotypes, and the interference factors. This information may provide us a better understanding of the pathogenesis of X-linked epilepsy and may contribute to clinical diagnosis and therapy of epilepsy.     

Concurrent Bilateral Renal Angiomyolipoma and Renal Cell Carcinoma in a Patient With Tuberous Sclerosis Complex

Renal angiomyolipomas (AMLs) are often associated with tuberous sclerosis. These tumors are predominantly benign, although malignant forms do exist and are known to be associated with renal cell carcinoma. This case report describes a patient with tuberous sclerosis and massive bilateral AML. Total right nephrectomy was performed; histopathologic examination revealed the coexistence of AML and clear cell renal carcinoma in the same kidney. Because differentiation between renal cell carcinoma and AML with minimal or no fat component can be difficult, an accurate diagnosis is critical in the management of renal AML.Key words: Angiomyolipoma, Renal cell carcinoma, Tuberous sclerosisApproximately 80% of patients with tuberous sclerosis complex (TSC) develop renal angiomyolipoma (AML). Although often benign,^1,2 malignant AML and renal cell carcinoma (RCC) have also been reported in patients with TSC. The concurrence of renal AML and RCC in the same kidney has also been reported in patients with TSC and has been revealed on pathologic examination.Several criteria can be used to help predict malignancy in renal AML, such as tumor size, tumor size and necrosis, and atypical mitotic figures. We report a case of associated massive bilateral AML and RCC. We discuss the diagnosis and treatment of renal AML and emphasize the possibility of concurrent renal malignancies in patients with TSC.     

Primary cells derived from Tuberous Sclerosis Complex patients show autophagy alteration in the haploinsufficiency state

Tuberous sclerosis complex (TSC) is an autosomal dominant cancer predisposition disorder caused by heterozygous mutations in TSC1 or TSC2 genes and characterized by mTORC1 hyperactivation. TSC-associated tumors develop after loss of heterozygosity mutations and their treatment involves the use of mTORC1 inhibitors. We aimed to evaluate cellular processes regulated by mTORC1 in TSC cells with different mutations before tumor development. Flow cytometry analyses were performed to evaluate cell viability, cell cycle and autophagy in non-tumor primary TSC cells with different heterozygous mutations and in control cells without TSC mutations, before and after treatment with rapamycin (mTORC1 inhibitor). We did not observe differences in cell viability and cell cycle between the cell groups. However, autophagy was reduced in mutated cells. After rapamycin treatment, mutated cells showed a significant increase in the autophagy process (p=0.039). We did not observe differences between cells with distinct TSC mutations. Our main finding is the alteration of autophagy in non-tumor TSC cells. Previous studies in literature found autophagy alterations in tumor TSC cells or knock-out animal models. We showed that autophagy could be an important mechanism that leads to TSC tumor formation in the haploinsufficiency state. This result could guide future studies in this field.     

Tuberous Sclerosis and Cardiac Arrhythmia in Three Zulu Patients

Cardiac arrhythmias, in the form of multiple atrial or ventricular extrasystoles together with various types of conduction defect, occurred in three Zulu patients with tuberous sclerosis. Probably this association occurs more often than has been suspected.