Tuberous Sclerosis

About this condition

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder affecting approximately 1 in 6,000 to 1 in 10,000 individuals, caused by mutations in TSC1 or TSC2. These genes encode proteins that regulate the mammalian target of rapamycin (mTOR) signaling pathway — a master controller of cell growth. Loss-of-function TSC1 or TSC2 variants cause mTOR hyperactivation, driving excessive cell growth and benign tumor formation throughout the body. TSC manifests as cortical tubers in the brain, subependymal giant cell astrocytomas (SEGAs), angiomyolipomas in the kidneys, skin manifestations (hypomelanotic macules, angiofibromas), and lymphangioleiomyomatosis in the lungs.

Neurological manifestations dominate the TSC disease burden: approximately 80–90% of patients develop epilepsy, often with seizure onset in infancy. Developmental delay and intellectual disability occur variably. Autism spectrum disorder is common. Approximately 33% of TSC cases are de novo mutations. Critically, TSC2 mutations account for approximately 70% of cases and are associated with significantly more severe disease phenotype — earlier seizure onset, higher rates of intellectual disability, and greater tumor burden. TSC1 mutations (~30% of cases) typically produce milder phenotypes with later seizure onset and better cognitive outcomes. Over 1,000 distinct TSC1/TSC2 variants have been identified.

Genotype-phenotype correlation informs surveillance intensity and prognostic counseling. TSC2-positive families should expect more aggressive disease requiring intensive brain and kidney surveillance. A confirmed TSC1 or TSC2 diagnosis mandates comprehensive protocols: brain MRI every 1–3 years to monitor SEGA development (SEGAs cause hydrocephalus and require intervention); renal imaging every 1–3 years for angiomyolipoma and cystic disease assessment; and cardiac echocardiography in infancy. Everolimus (Votubia), an FDA-approved mTOR inhibitor, directly targets the molecular consequence of TSC loss — shrinking SEGAs and angiomyolipomas while improving long-term outcomes. This represents one of the most successful gene-to-drug examples in rare disease.

TSC2 mutations cause more severe disease with earlier seizure onset and higher tumor burden; TSC1 mutations typically produce milder phenotypes with better long-term outcomes.

Gene locus: TSC1 (9q34.13), TSC2 (16p13.3)

TSC1/TSC2 panels are relatively comprehensive but miss large deletions and regulatory variants. De novo detection can be challenging without parental comparison.

Structural variants in TSC1/TSC2 may escape standard panel detection

Although TSC1 and TSC2 are the only genes associated with tuberous sclerosis, standard targeted panels capture most coding sequence but frequently miss large deletions, intronic variants, and regulatory region changes. De novo variant detection can be challenging in sporadic cases if parental samples are not available for comparison. Approximately one-third of TSC cases are de novo, and comprehensive molecular diagnosis in these cases can be elusive with panel-based approaches. Whole genome sequencing provides complete TSC1/TSC2 coverage and enables detection of large structural variants and intronic changes that targeted approaches miss.

Genotype predicts disease severity and guides surveillance intensity

A TSC2 pathogenic variant predicts significantly more aggressive disease — earlier seizure onset, higher rates of intellectual disability, greater tumor burden, and earlier SEGA development requiring mTOR inhibitor intervention. A TSC1 variant typically predicts milder disease with later seizure onset and better cognitive outcomes. This genotype-phenotype correlation directly informs surveillance protocols: TSC2 families require more intensive brain imaging surveillance and lower thresholds for mTOR inhibitor initiation. Everolimus therapy can be started earlier in TSC2 patients to prevent SEGA progression. Cascade family screening identifies first-degree relatives.

Seizures in childhood. Skin findings that didn't make sense. A condition caused by one of two genes — where identifying which one shapes the treatment plan and the monitoring schedule.