Intellectual ability in tuberous sclerosis complex correlates with predicted effects of mutations on TSC1 and TSC2 proteins

The Genetics of Tuberous Sclerosis Complex and Related mTORopathies: Current Understanding and Future Directions

The mechanistic target of rapamycin (mTOR) pathway serves as a master regulator of cell growth, proliferation, and survival. Upregulation of the mTOR pathway has been shown to cause malformations of cortical development, medically refractory epilepsies, and neurodevelopmental disorders, collectively described as mTORopathies. Tuberous sclerosis complex (TSC) serves as the prototypical mTORopathy. Characterized by the development of benign tumors in multiple organs, pathogenic variants in TSC1 or TSC2 disrupt the TSC protein complex, a negative regulator of the mTOR pathway. Variants in critical domains of the TSC complex, especially in the catalytic TSC2 subunit, correlate with increased disease severity. Variants in less crucial exons and non-coding regions, as well as those undetectable with conventional testing, may lead to milder phenotypes. Despite the assumption of complete penetrance, expressivity varies within families, and certain variants delay disease onset with milder neurological effects. Understanding these genotype-phenotype correlations is crucial for effective clinical management. Notably, 15% of patients have no mutation identified by conventional genetic testing, with the majority of cases postulated to be caused by somatic TSC1/TSC2 variants which present complex diagnostic challenges. Advancements in genetic testing, prenatal screening, and precision medicine hold promise for changing the diagnostic and treatment paradigm for TSC and related mTORopathies. Herein, we explore the genetic and molecular mechanisms of TSC and other mTORopathies, emphasizing contemporary genetic methods in understanding and diagnosing the condition.

Emerging Link between Tsc1 and FNIP Co-Chaperones of Hsp90 and Cancer

Heat shock protein-90 (Hsp90) is an ATP-dependent molecular chaperone that is tightly regulated by a group of proteins termed co-chaperones. This chaperone system is essential for the stabilization and activation of many key signaling proteins. Recent identification of the co-chaperones FNIP1, FNIP2, and Tsc1 has broadened the spectrum of Hsp90 regulators. These new co-chaperones mediate the stability of critical tumor suppressors FLCN and Tsc2 as well as the various classes of Hsp90 kinase and non-kinase clients. Many early observations of the roles of FNIP1, FNIP2, and Tsc1 suggested functions independent of FLCN and Tsc2 but have not been fully delineated. Given the broad cellular impact of Hsp90-dependent signaling, it is possible to explain the cellular activities of these new co-chaperones by their influence on Hsp90 function. Here, we review the literature on FNIP1, FNIP2, and Tsc1 as co-chaperones and discuss the potential downstream impact of this regulation on normal cellular function and in human diseases.

Tuberous Sclerosis Complex: Early Screening and Infant Outcome in NICU

OBJECTIVE

We describe the clinical and genetic features, drug use and neuropsychiatric disorders of infants diagnosed with tuberous sclerosis complex (TSC) within 3 months of age at a neonatal intensive care unit (NICU) to better understand the different outcomes from early screening.

METHODS

In this retrospective study, we consisted of 42 infants with a definitive TSC diagnosis by genetic criteria (TSC1 = 8, TSC2 = 34). The different phenotypes and outcomes between patients with TSC1 and TSC2 mutations were analyzed.

RESULTS

The most common initial presenting features of TSC were cortical tubers on magnetic resonance imaging (50%), hypomelanotic macules on skin (47.61%) and spasm (42.85%), when they were diagnosed. Following disease progression to time of follow-up 1 year later, we found that the rate of epilepsy increased from 42.85% to 75.61% and that of cardiac rhabdomyoma increased from 28.57% to 43.9%. The median age at first presentation was 7.84 ± 1.88 months. We also found that 54.83% of patients on medication were seizure free for over 1 year, and that 43.9% of patients have intellectual disability. In total, 42 variants of TSC were detected, including 12 novel variants. We found no evidence of an association between different clinical features and their outcomes among patients with different gene mutations.

CONCLUSION

Early diagnosis of TSC in NICU opens a window of opportunity for early, more effective treatment of epilepsy as well as reduces the risk of neurological conditions.

TSC-associated neuropsychiatric disorders (TAND): findings from the TOSCA natural history study

Background

Most evidence for TSC-associated neuropsychiatric disorders (TAND) to date have come from small studies and case reports, and very little is known about TAND in adults. We explored baseline TAND data from the large-scale international TOSCA natural history study to compare childhood and adult patterns, describe age-based patterns, and explore genotype-TAND correlations.

Results

The study enrolled 2216 eligible participants with TSC from 170 sites across 31 countries at the data cut-off for the third interim analysis (data cut-off date: September 30, 2015). The most common behavioural problems (reported in > 10% of participants) were overactivity, sleep difficulties, impulsivity, anxiety, mood swings, severe aggression, depressed mood, self-injury, and obsessions. Psychiatric disorders included autism spectrum disorder (ASD, 21.1%), attention deficit hyperactivity disorder (ADHD, 19.1%), anxiety disorder (9.7%), and depressive disorder (6.1%). Intelligence quotient (IQ) scores were available for 885 participants. Of these, 44.4% had normal IQ, while mild, moderate, severe, and profound degrees of intellectual disability (ID) were observed in 28.1, 15.1, 9.3, and 3.1%, respectively. Academic difficulties were identified in 58.6% of participants, and neuropsychological deficits (performance <5th percentile) in 55.7%. Significantly higher rates of overactivity and impulsivity were observed in children and higher rates of anxiety, depressed mood, mood swings, obsessions, psychosis and hallucinations were observed in adults. Genotype-TAND correlations showed a higher frequency of self-injury, ASD, academic difficulties and neuropsychological deficits in TSC2. Those with no mutations identified (NMI) showed a mixed pattern of TAND manifestations. Children and those with TSC2 had significantly higher rates of intellectual disability, suggesting that age and genotype comparisons should be interpreted with caution.

Conclusions

These results emphasize the magnitude of TAND in TSC and the importance of evaluating for neuropsychiatric comorbidity in all children and adults with TSC, across TSC1 and TSC2 genotypes, as well as in those with no mutations identified. However, the high rates of unreported or missing TAND data in this study underline the fact that, even in expert centres, TAND remains underdiagnosed and potentially undertreated.

A clinical update on tuberous sclerosis complex-associated neuropsychiatric disorders (TAND)

Tuberous sclerosis complex (TSC) is associated with a wide range of behavioral, psychiatric, intellectual, academic, neuropsychological, and psychosocial difficulties, which are often underdiagnosed and undertreated. Here, we present a clinical update on TSC-associated neuropsychiatric disorders, abbreviated as "TAND," to guide screening, diagnosis, and treatment in practice. The review is aimed at clinical geneticists, genetic counselors, pediatricians, and all generalists involved in the assessment and treatment of children, adolescents and adults with TSC, and related disorders. The review starts with a summary of the construct and levels of TAND, before presenting up-to-date information about each level of investigation. The review concludes with a synopsis of current and future TAND research.

Early predictors of clinical and mental outcome in tuberous sclerosis complex: A prospective study

AIM

We aimed to identify early predictors of intractable epilepsy, intellectual disability (ID) and autism spectrum disorders (ASD) in the cohort of TSC patients initially diagnosed with cardiac rhabdomyomas (CR).

METHOD

Over the period of twelve years we prospectively obtained clinical, neuropsychological, electrophysiological and neuroimaging data in a group of 22 TSC patients (9 females, 13 males) with the pre/perinatal diagnosis of CR, included to the study at the time of diagnosis. Afterwards, we statistically determined variables associated with ID, ASD and intractable epilepsy.

RESULTS

Development of ID was predicted by severe epilepsy (a higher number of anti-epileptic drugs used), a higher number of dysplastic lesions on MRI, and abnormal background activity on EEG (p < 0.05). Predictors of ASD included early developmental delay, abnormal background activity on EEG at the end of follow-up and a higher number of areas with dysplastic features on MRI (p < 0.05). Intractable epilepsy was associated with a higher number of areas with dysplastic features on MRI, ID and with TSC2 genotype.

CONCLUSION

Adverse mental and clinical outcome was associated with intractable epilepsy and the severe anatomical brain involvement; therefore, our centre developed a tailored protocol for early identification of TSC patients at a higher risk of developing intractable epilepsy with its deleterious effect on cognitive outcome.

Epilepsy may be the major risk factor of mental retardation in children with tuberous sclerosis: A retrospective cohort study

Mental retardation (MR) is one of the most common cognitive comorbidities in children with tuberous sclerosis, and there are enormous studies about its risk factors. The genetic difference and the severity of epilepsy are the two main factors, but their weight in the occurrence of MR is still unclear. Two hundred twenty-three patients with tuberous sclerosis who received intelligence assessment, genetic mutation analysis, and the epilepsy severity assessment were included in our study. Genotype-neurocognitive phenotype correlations and epilepsy-neurocognitive phenotype correlations were analyzed by binary logistic regression analysis. No statistical significant result was found on genotype-neurocognitive phenotype correlations, which contrasted the previous report. The prevalence of MR was 50.0% for the patients with tuberous sclerosis complex-1 (TSC1) mutation, 54.5% for TSC2 (p=0.561), 54.7% for patients with protein-truncating (PT) and 50.0% for patients with nontruncating (NT) (p=0.791), and 54.3% for patients with family history and 53.7% for patients without family history (p=0.748). Statistical significant results were found on epilepsy-neurocognitive phenotype correlations, both on E-chess score (p=0.01) and the occurrence of infantile spasms (p=0.014), which was consistent to the previous study. For children with tuberous sclerosis, instead of genetic factors, epilepsy may play the main role for the presence of mental retardation. Patients with mental retardation tend to have earlier seizure attack, take more AEDs, have more seizure types, and have higher seizure frequency. Among the four cognitive functions in Denver II, social ability and language ability are more vulnerable to be influenced than fine and gross motor ability.

New insights into the pathogenesis and prevention of tuberous sclerosis-associated neuropsychiatric disorders (TAND)

Tuberous sclerosis complex (TSC) is a multi-system disorder resulting from mutations in either the TSC1 or TSC2 genes leading to hyperactivation of mechanistic target of rapamycin (mTOR) signaling. TSC is commonly associated with autism (61%), intellectual disability (45%), and behavioral, psychiatric, intellectual, academic, neuropsychological, and psychosocial difficulties that are collectively referred to as TSC-associated neuropsychiatric disorders (TAND). More than 90% of children with TSC have epilepsy, including infantile spasms, and early onset of seizures, especially infantile spasms, is associated with greater impairment in intellectual development compared with individuals with TSC without seizures. Development of the mTOR inhibitors everolimus and sirolimus has led to considerable progress in the treatment of renal angiomyolipomata, pulmonary lymphangioleiomyomatosis, and subependymal giant cell astrocytomas in the brain. However, similar therapeutic progress is needed in the treatment of TAND.

Molecular, clinical and neuropsychological study in 31 patients with Kabuki syndrome and KMT2D mutations

Kabuki syndrome (KS-OMIM 147920) is a rare developmental disease characterized by the association of multiple congenital anomalies and intellectual disability. This study aimed to investigate intellectual performance in children with KS and link the performance to several clinical features and molecular data. We recruited 31 children with KMT2D mutations who were 6 to 16 years old. They all completed the Weschler Intelligence Scale for Children, fourth edition. We calculated all indexes: the Full Scale Intellectual Quotient (FSIQ), Verbal Comprehension Index (VCI), Perceptive Reasoning Index (PRI), Processing Speed Index (PSI), and Working Memory Index (WMI). In addition, molecular data and several clinical symptoms were studied. FSIQ and VCI scores were 10 points lower for patients with a truncating mutation than other types of mutations. In addition, scores for FSIQ, VCI and PRI were lower for children with visual impairment than normal vision. We also identified a discrepancy in indexes characterized by high WMI and VCI and low PRI and PSI. We emphasize the importance of early identification and intensive care of visual disorders in patients with KS and recommend individual assessment of intellectual profile.

Interdependence of clinical factors predicting cognition in children with tuberous sclerosis complex

Cognitive development in patients with tuberous sclerosis complex is highly variable. Predictors in the infant years would be valuable to counsel parents and to support development. The aim of this study was to confirm factors that have been reported to be independently correlated with cognitive development. 102 patients included in this study were treated at the ENCORE-TSC expertise center of the Erasmus Medical Center-Sophia Children’s Hospital. Data from the first 24 months of life were used, including details on epilepsy, motor development and mutation status. Outcome was defined as cognitive development (intellectual equivalent, IE) as measured using tests appropriate to the patients age and cognitive abilities (median age at testing 8.2 years, IQR 4.7–12.0). Univariable and multivariable regression analyses were used. In a univariable analysis, predictors of lower IE were: the presence of infantile spasms (β = −18.3, p = 0.000), a larger number of antiepileptic drugs used (β = −6.3, p = 0.000), vigabatrin not used as first drug (β = −14.6, p = 0.020), corticosteroid treatment (β = −33.2, p = 0.005), and a later age at which the child could walk independently (β = −2.1, p = 0.000). An older age at seizure onset predicted higher IE (β = 1.7, p = 0.000). In a multivariable analysis, only age at seizure onset was significantly correlated to IE (β = 1.2, p = 0.005), contributing to 28% of the variation in IE. In our cohort, age at seizure onset was the only variable that independently predicted IE. Factors predicting cognitive development could aid parents and physicians in finding the appropriate support and schooling for these patients.

Genotype and brain pathology phenotype in children with tuberous sclerosis complex

Structural brain malformations associated with Tuberous Sclerosis Complex (TSC) are related to the severity of the clinical symptoms and can be visualized by magnetic resonance imaging (MRI). Tuberous Sclerosis Complex is caused by inactivating TSC1 or TSC2 mutations. We investigated associations between TSC brain pathology and different inactivating TSC1 and TSC2 variants, and examined the potential prognostic value of subdivision of TSC2 variants based on their predicted effects on TSC2 expression. We performed genotype-phenotype associations of TSC-related brain pathology on a cohort of 64 children aged 1.4-17.9 years. Brain abnormalities were assessed using MRI. Individuals were grouped into those with an inactivating TSC1 variant and those with an inactivating TSC2 variant. The TSC2 group was subdivided into changes predicted to result in TSC2 protein expression (TSC2p) and changes predicted to prevent expression (TSC2x). The TSC2 group was associated with more and larger tubers, more radial migration lines, and more subependymal nodules than the TSC1 group. Subependymal nodules were also more likely to be calcified. Subdivision of the TSC2 group did not reveal additional, substantial differences, except for a larger number of tubers in the temporal lobe and a larger fraction of cystic tubers in the TSC2x subgroup. The severity of TSC-related brain pathology was related to the presence of an inactivating TSC2 variant. Although larger studies might find specific TSC2 variants that have prognostic value, in our cohort, subdivision of the TSC2 group did not lead to better prediction.

Tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that affects multiple organ systems and is caused by loss-of-function mutations in one of two genes: TSC1 or TSC2. The disorder can affect both adults and children. First described in depth by Bourneville in 1880, it is now estimated that nearly 2 million people are affected by the disease worldwide. The clinical features of TSC are distinctive and can vary widely between individuals, even within one family. Major features of the disease include tumours of the brain, skin, heart, lungs and kidneys, seizures and TSC-associated neuropsychiatric disorders, which can include autism spectrum disorder and cognitive disability. TSC1 (also known as hamartin) and TSC2 (also known as tuberin) form the TSC protein complex that acts as an inhibitor of the mechanistic target of rapamycin (mTOR) signalling pathway, which in turn plays a pivotal part in regulating cell growth, proliferation, autophagy and protein and lipid synthesis. Remarkable progress in basic and translational research, in addition to several randomized controlled trials worldwide, has led to regulatory approval of the use of mTOR inhibitors for the treatment of renal angiomyolipomas, brain subependymal giant cell astrocytomas and pulmonary lymphangioleiomyomatosis, but further research is needed to establish full indications of therapeutic treatment. In this Primer, we review the state-of-the-art knowledge in the TSC field, including the molecular and cellular basis of the disease, medical management, major knowledge gaps and ongoing research towards a cure.

Towards an improved understanding of TSC-Associated Neuropsychiatric Disorders (TAND)

Purpose

– Tuberous Sclerosis Complex (TSC) is associated with many learning, behavioural, neurodevelopmental and psychiatric difficulties. Over 90 per cent of those with TSC will have some of these concerns, yet typically no more than 20 per cent receive support and treatment. The purpose of this paper is to provide an overview of TSC-Associated Neuropsychiatric Disorders (TAND), explore barriers to identification and management of TAND, and propose possible next steps to improve assessment and treatment of TAND.

Design/methodology/approach

– The paper combines a brief review of the multiple levels of TAND with a conceptual analysis of barriers and potential facilitators to assessment and intervention for TAND.

Findings

– Results suggest that the perceived uniqueness of TAND leads to treatment paralysis for most healthcare professionals, thus explaining the assessment and treatment gap seen for TAND. This may in part be due to the multi-dimensionality of TAND, and in part due to lack of access to clear, useful and evidence-based resources for TAND.

Research limitations/implications

– Identification of natural TAND clusters through machine-based learning and data reduction methodologies may yield a manageable number of natural groups of TSC-related neuropsychiatric problems, for which a basic “toolkit” of evidence-based interventions could be developed.

Practical implications

– Families and clinicians will benefit from a toolkit of tried and tested resources and evidence-based information to guide further investigation and management of TAND.

Originality/value

– Even though individuals will have unique TAND profiles, there may be key natural TAND clusters – combinations of behaviours across multi-dimensional levels – that will simplify and improve access to further evaluation, treatment and neuroscientific research.