Minimal mosaicism, maximal phenotype: Discordance between clinical and molecular findings in two patients with tuberous sclerosis

Fetal and neonatal cardiac tumor diagnosed as Tuberous Sclerosis associated rhabdomyomas resulting from novel pathogenic missense variant detected in TSC2 gene: A case report

Fetal cardiac tumors are often the first clinical manifestation of tuberous sclerosis (TS) when fetal ultrasound screening is performed. TS is an autosomal dominant disorder caused by the mutations in TSC1 or TSC2 genes. Here we report a case of a patient with a fetal and neonatal cardiac tumor who underwent a genetic analysis for TS after birth. Multiple fetal cardiac tumors were detected on ultrasonography at 24 weeks, gestation with no other manifestation. Neither epilepsy nor mental retardation was seen after birth. Once the parents were provided careful genetic counseling, a genetic analysis for TS was performed when the patient was 2 years old that demonstrated a novel pathogenic missense variant: c.1072T>C, p.Trp358Arg in the TSC2 gene with 30% mosaicism. This pathogenic variant is located on exon 10 of the TSC2 gene, which encodes the hamartin binding domain, leading to impair inhibitory function of the hamartin-tuberin complex, which activates mammalian target of rapamycin(mTOR) activity. The cardiac tumors were diagnosed as rhabdomyomas, a major clinical feature of TS, since the penetrance of this gene variants are thought to be 100%. We speculate that this new missense variant in TSC2 gene with 30% mosaicism will be associated to the milder phenotype of TS since the regression of the rhabdomyomas is the only manifestation in this patient. We hope that this case report might help clinicians and genetic counselors manage individualized surveillance plans for patients with TS.

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.

Identification of a novel heterozygous TSC2 splicing variant in a patient with Tuberous sclerosis complex: A case report

RATIONALE

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder characterized by facial angiofibromas, epilepsy, intellectual disability, and the development of hamartomas in several organs, including the heart, kidneys, brain, and lungs. Mutations in either TSC1 or TSC2 result in dysregulated mTOR activation, leading to the occurrence of TSC.

PATIENT CONCERNS

A 44-year-old man was hospitalized for acute lumbago and hematuria.

DIAGNOSIS

The patient presented with facial angiofibromas, epilepsy, fibrous plaques, periungual fibroma, renal angiomyolipomas (AML), pulmonary lymphangioleiomyomatosis (LAM), liver hamartomas, and osteosclerosis. A diagnosis of TSC was made based on clinical manifestations.

INTERVENTIONS

Next-generation sequencing (NGS) was performed to screen for potential variants, which were verified using Sanger sequencing. The final variant was analyzed using a minigene assay.

OUTCOMES

A potentially pathogenic novel TSC2 variant (NM_000548.4, c.336_336 + 15delGGTAAGGCCCAGGGCG) was identified using NGS and confirmed using Sanger sequencing. The in vitro minigene assay showed that the variant c.336_336 + 15delGGTAAGGCCCAGGGCG caused erroneous integration of a 74 bp sequence into intron 4. This novel variant was not found in his unaffected parents or 100 unrelated healthy controls.

LESSONS

We identified a novel heterozygous TSC2 variant, c.336_336 + 15delGGTAAGGCCCAGGGCG, in a patient with classical TSC and demonstrated that this variant leads to aberrant splicing using a minigene assay. Our results extend the understanding of the mutational spectrum of TSC2.

Diagnostic features of tuberous sclerosis complex: case report and literature review

Tuberous sclerosis complex (TSC) is a rare autosomal dominant genetic syndrome that is caused by mutations in the tumour suppressor genes TSC1 or TSC2 which causes multiorgan growths. TSC presents at any age as a wide range of clinical and phenotypic manifestations with varying severity. The main goal of this article was to state two cases of TSC and review the most commonly reported major and minor diagnostic clinical features and the most common features that led to an investigation of possible TSC diagnosis. Herein, we report two cases of TSC, which both presented with seizures during the first 6 months of life. Case 1 presented with multiple types of seizures from 6 months of age and was diagnosed by multiple calcified subependymal nodules (SENs) detected by computed tomography and magnetic resonance imaging (MRI). Case 2 presented with seizures from 3 months of age and was diagnosed prenatally when a tumour was seen in her heart during antenatal ultrasonography. In conclusion, the literature review revealed that neurological manifestations (mainly seizures) were the main feature that led to investigation and diagnosis of TSC followed by abdominal manifestations (mainly renal features) and antenatal follow-up imaging. Other manifestations in skin, chest, eyes, teeth and heart rarely led to TSC diagnosis. In some cases, TSC was incidentally discovered by medical imaging. The cortical tubers, SENs, and subependymal giant cell astrocytomas brain lesions were the most commonly reported major features. Skin features including angiofibromas, ungual fibromas and shagreen patch were the second most common major features reported in the literature. However, skin manifestations were not a common led to investigation and diagnosis of TSC. Renal features, mainly angiomyolipomas (AMLs), were the third most common major feature reported. Medical imaging plays an essential role in diagnosis of TSC, and clinical features are important clues that lead to investigation for the disease.

Low-level mosaicism in tuberous sclerosis complex in four unrelated patients: Comparison of clinical characteristics and diagnostic pathways

Tuberous sclerosis complex (TSC) is an autosomal dominant neurocutaneous syndrome caused by either TSC1 or TSC2 gene mutations. About 15% of TSC patients remain without genetic diagnosis by conventional analysis despite clinical evidence. It is important to identify somatic mosaics, as therapeutic options are now available in patients with TSC1 or TSC2 mutations. Here, we describe the clinical and genetic characteristics of four male TSC patients with low‐level mosaicism. Patients presented at ages between 9 months and 32 years. Clinical manifestations varied considerably and included brain lesions in all four patients, cardiac rhabdomyomas in two young patients, skin involvement in two patients, and retinal hamartomas and renal angiomyolipomas in three patients. One patient presented with epileptic seizures and psychomotor delay. Low levels of mosaicism for TSC1 or TSC2 mutation were found in different tissue samples employing next generation sequencing and multiple ligation‐dependent probe amplification. The five disease‐associated variants, including one second‐hit mutation, include three truncating mutations and one deletion in TSC2, and one truncating mutation in TSC1. Sanger sequencing, allele‐specific oligonucleotide PCR (ASO‐PCR), and droplet digital PCR were used to confirm and quantify the disclosed mutations. Genetic identification of low‐level mosaicism for TSC remains challenging but is important for optimal surveillance and management.

Targeted deep sequencing of DNA from multiple tissue types improves the diagnostic rate and reveals a highly diverse phenotype of mosaic neurofibromatosis type 2

BACKGROUND

Although 60% of patients with de novo neurofibromatosis type 2 (NF2) are presumed to have mosaic NF2, the actual diagnostic rate of this condition remains low at around 20% because of the existing difficulties in detecting NF2 variants with low variant allele frequency (VAF). Here, we examined the correlation between the genotype and phenotype of mosaic NF2 after improving the diagnostic rate of mosaic NF2.

METHODS

We performed targeted deep sequencing of 36 genes including NF2 using DNA samples from multiple tissues (blood, buccal mucosa, hair follicle and tumour) of 53 patients with de novo NF2 and elucidated their genotype-phenotype correlation.

RESULTS

Twenty-four patients (45.2%) had the NF2 germline variant, and 20 patients with NF2 (37.7%) had mosaic NF2. The mosaic NF2 phenotype was significantly different from that in patients with NF2 germline variant in terms of distribution of NF2-related disease, tumour growth rate and hearing outcome. The behaviour of schwannoma correlated to the extent of VAF with NF2 variant in normal tissues unlike meningioma.

CONCLUSION

We have improved the diagnostic rate of mosaic NF2 compared with that of previous studies by targeted deep sequencing of DNA from multiple tissues. Many atypical patients with NF2 diagnosed with 'unilateral vestibular schwannoma' or 'multiple meningiomas' presumably have mosaic NF2. Finally, we suggest that the highly diverse phenotype of NF2 could result not only from the type and location of NF2 variant but also the extent of VAF in the NF2 variant within normal tissue DNA.

Individual Copy Number of Ribosomal Genes as a Factor of Mental Retardation and Autism Risk and Severity

Autism is a complex multifactorial developmental disorder characterized by deficits in communication and restricted interests, often followed by mental retardation. Autism spectrum disorders (ASD) are caused by defects in miscellaneous molecular mechanisms, many of which remain unclear. But a considerable part of the known pathways converges on protein synthesis or degradation processes at different stages in the dendrites, laying the foundation for a concept of disturbed “translational homeostasis” or “proteostasis” in autism. The protein synthesis is conducted on ribosomes, cellular organelles consisting from a complex of riboproteins and a ribosomal RNA (rRNA) framework. The rRNA is encoded by ribosomal genes (RG) existing in multiple copies in the genome. The more copies of RG that are contained in the genome, the higher is the peak (maximum possible) ribosome abundance in the cell. A hypothesis is proposed that the RG copy number, through determining the quantity of ribosomes available in the dendrites, modulates the level of local dendritic translation and thus is a factor of risk and severity of a series of neuropsychiatric disorders caused by aberrant dendritic translation. A carrier of very low copy number of ribosomal genes is expected to have a milder form of ASD than a subject with the same epigenetic and genetic background, but a higher ribosomal gene dosage. Various ways of evaluation and testing the hypothesis on clinical material and animal models are suggested.