Genetics, genomics, and genotype-phenotype correlations of TSC: Insights for clinical practice

Mutational analysis of renal angiomyolipoma associated with tuberous sclerosis complex and the outcome of short-term everolimus therapy

To identify clinical characteristics and mutation spectra in Chinese patients with renal angiomyolipoma (AML) associated with the tuberous sclerosis complex (TSC, TSC-AML), examined the efficacy and safety of short-term everolimus therapy (12 weeks). We analyzed the frequency distribution of each TSC-related clinical feature and investigated gene mutations by genetic testing. Some subjects received everolimus for 12 weeks at a dose of 10 mg/day, and the efficacy and safety of short-term everolimus therapy were examined. Finally, 82 TSC-AML patients were enrolled for analysis in this study. Of the 47 patients who underwent genetic testing, 22 patients (46.81%) had at least one detectable mutation in the TSC1 or TSC2 gene: 7 were TSC1 gene mutations, 13 were TSC2 gene mutations, and 2 were found in both TSC1 and TSC2. Everolimus treatment had a statistically significant effect on the renal AML volume reduction during follow-up (P < 0.05), and the mean reduction rate of volume for all cases was 56.47 ± 23.32% over 12 weeks. However, 7 patients (7/25; 28.00%) experienced an increase in renal AML tumor volume within 12 weeks after discontinuation of the everolimus treatment. Although most patients (27/30, 90.00%) experienced some adverse events during the treatment period, all such events were mild, and no patients discontinued or needed dose reduction because of adverse events. Overall, in this study, the mutation rate of TSC-AML patients is much lower than other reports. Short-term everolimus treatment for TSC-AML is effective and safe, but the stability is much lower than long-term therapy.

Constitutive activation of mTORC1 signaling induced by biallelic loss-of-function mutations in SZT2 underlies a discernible neurodevelopmental disease

There have been increasing number of reports of SZT2-related neurological diseases, the main symptoms of which are epilepsy, developmental delay, macrocephaly and a dysmorphic corpus callosum. SZT2 functions as a regulator of mechanistic target of rapamycin complex 1 (mTORC1) signaling in cultured human cell lines and mouse tissues. However, it remains to be determined whether mutations in SZT2 in human patients alter mTORC1 signaling. In this study, we aimed to investigate the functional consequence of biallelic SZT2 variants in Epstein-Barr virus-induced lymphoblastoid cell lines (LCLs) established from two patients with a typical SZT2-related neurodevelopmental disease. Increased phosphorylation of S6 kinase and S6 was identified in patient-derived cell lines under amino acid-starved condition, suggestive of constitutive hyperactivation of mTORC1 signaling. This result was validated by constitutive lysosomal localization of mTOR in patients’ LCLs. Furthermore, patients’ LCLs display an excessive response to slight amino acid stimulation. Our data suggest the loss-of-function nature of SZT2 mutations in the patients, and consequent hyperactivation of mTORC1 signaling in response to both amino acid starvation and stimulation in their LCLs. By these functional analyses, the pathogenicity of newly identified SZT2 variants can be determined, allowing for more detailed characterization of genotype-phenotype correlations.

Tuberous Sclerosis Complex Genotypes and Developmental Phenotype

BACKGROUND

Children with tuberous sclerosis complex (TSC), caused by pathogenic variants in TSC1/TSC2, are at risk for intellectual disability. TSC2 pathogenic variants appear to increase the risk, compared with TSC1. However, the effect of TSC2 pathogenic variants on early and specific domains of development hasn't been studied. Using an extensively phenotyped group, we aimed to characterize differences in early intellectual development between genotypes.

METHODS

The study group (n = 92) included participants with TSC enrolled in a multicenter study involving genetic testing and detailed prospective phenotyping including the Mullen Scales of Early Learning, a validated measure of cognition, language, and motor development in babies and preschool children. Mean T-scores at 24 months for each Mullen Scales of Early Learning domain were calculated for children with, versus without, a TSC2 pathogenic variant. Multivariable linear regression models were used to compare the groups, adjusting for seizures.

RESULTS

T-scores on every Mullen Scales of Early Learning domain were significantly worse in the TSC2 group. Below average composite scores were present in three-fourths of the TSC2 group, compared with one-fourth of those without TSC2. Having a TSC2 pathogenic variant was associated with lower composite Mullen Scales of Early Learning scores, even when corrected for seizures.

CONCLUSIONS

In a well-characterized patient population with standardized assessment of multiple aspects of development, we found that having a TSC2 pathogenic variant was associated with significantly lower Mullen Scales of Early Learning scores at age 24 months, independent of seizures. These data suggest that a baby with a TSC2 pathogenic variant is at high risk for significant developmental delays by 24 months.

A step-wise approach for establishing a multidisciplinary team for the management of tuberous sclerosis complex: a Delphi consensus report

Background

Tuberous sclerosis complex (TSC) is a rare autosomal dominant genetic disorder associated with mutations in TSC1 and TSC2 genes, upregulation of mammalian target of rapamycin signaling, and subsequent tumor formation in various organs. Due to the many manifestations of TSC and their potential complications, management requires the expertise of multiple medical disciplines. A multidisciplinary care approach is recommended by consensus guidelines. Use of multidisciplinary teams (MDTs) has been shown to be beneficial in treating other complex diseases, such as cancer. In a lifelong disease such as TSC, an MDT may facilitate the transition from pediatric to adult care. However, little guidance exists in the literature regarding how to organize an MDT in TSC.

Methods

To discuss the best approach to assembling an MDT, this project was initiated in October 2017 with a meeting of 12 physicians from various specialties and various countries. Following this first meeting, the experts generated statements on the most important aspects to implement in establishing an MDT for TSC by 3 rounds of selection using a Delphi process via electronic correspondence. Finally, TSC patient advocates reviewed the findings and provided additional insights from a patient perspective.

Results

A 3-step roadmap was recommended, starting with identifying a single individual to begin organizing care (Step 1), then establishing a small core team (Step 2), and finally, establishing a larger multi-disciplinary team (Step 3). Because of the multisystemic nature of TSC, the MDT should include specialists such as a neurologist, a neurosurgeon, a nephrologist, a urologist, a pulmonologist, an ophthalmologist, a cardiologist, a dermatologist, a geneticist, and a psychiatrist/psychologist. The MDT should recommend a care plan for each patient based on the individual’s needs and in consultation with him/her or his/her family. Some of the most important aspects of an MDT that were agreed upon included identifying a case manager to help coordinate care, providing access to health care professionals of varying specialties, and including a lead physician who takes medical responsibility for patients’ overall care.

Conclusions

The results of our consensus provide guidance to support the initiation of an MDT in TSC.

Genetic Etiologies, Diagnosis, and Treatment of Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that affects multiple organ systems due to an inactivating variant in either TSC1 or TSC2, resulting in the hyperactivation of the mechanistic target of rapamycin (mTOR) pathway. Dysregulated mTOR signaling results in increased cell growth and proliferation. Clinically, TSC patients exhibit great phenotypic variability, but the neurologic and neuropsychiatric manifestations of the disease have the greatest morbidity and mortality. TSC-associated epilepsy occurs in nearly all patients and is often difficult to treat because it is refractory to multiple antiseizure medications. The advent of mTOR inhibitors offers great promise in the treatment of TSC-associated epilepsy and other neurodevelopmental manifestations of the disease; however, the optimal timing of therapeutic intervention is not yet fully understood.

Uncovering Missing Heritability in Rare Diseases

The problem of 'missing heritability' affects both common and rare diseases hindering: discovery, diagnosis, and patient care. The 'missing heritability' concept has been mainly associated with common and complex diseases where promising modern technological advances, like genome-wide association studies (GWAS), were unable to uncover the complete genetic mechanism of the disease/trait. Although rare diseases (RDs) have low prevalence individually, collectively they are common. Furthermore, multi-level genetic and phenotypic complexity when combined with the individual rarity of these conditions poses an important challenge in the quest to identify causative genetic changes in RD patients. In recent years, high throughput sequencing has accelerated discovery and diagnosis in RDs. However, despite the several-fold increase (from ~10% using traditional to ~40% using genome-wide genetic testing) in finding genetic causes of these diseases in RD patients, as is the case in common diseases-the majority of RDs are also facing the 'missing heritability' problem. This review outlines the key role of high throughput sequencing in uncovering genetics behind RDs, with a particular focus on genome sequencing. We review current advances and challenges of sequencing technologies, bioinformatics approaches, and resources.