Tuberous Sclerosis Complex (TSC)
Introduction
Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by the development of benign tumors (hamartomas) in multiple organs, including the brain, skin, kidneys, heart, and lungs. This condition reveals huge clinical variability, ranging from mild cutaneous expressions to severe neurological impairment. TSC often presents in early childhood, with seizures, developmental delay, and characteristic skin lesions. The disorder is included in the neurocutaneous syndromes and has significant neurological and systemic manifestations.
Genetics
TSC is caused by pathogenic variants in the TSC1 (on chromosome 9q34) or TSC2 gene (on chromosome 16p13.3). These genes encode hamartin or tuberin, respectively. These protein complexes negatively regulate the target of rapamycin (mTOR) signaling pathway. This pathway is a critical regulator of cell metabolism, growth, and proliferation.
Loss-of-function mutations in TSC1 or TSC2 lead to hyperactivation of the mTOR pathway, resulting in uncontrolled cell growth and secondarily neoplastic formation. TSC follows an autosomal dominant inheritance, although approximately two-thirds of cases arise from de novo mutations.
Epidemiology
Tuberous sclerosis complex has a prevalence of 1 in 6,000–10,000 live births. It affects individuals of both sexes and all ethnic groups.
Pathophysiology
The pathophysiology of TSC is based on dysregulation of the mTOR signaling pathway. The TSC1–TSC2 protein complex normally inhibits mTOR activity; when this inhibition is lost, increased cellular growth, proliferation, and abnormal protein synthesis occur. This leads to the formation of hamartomas in multiple organs. In the central nervous system, cortical tubers, subependymal nodules, and subependymal giant cell astrocytomas (SEGAs) are characteristic lesions. These abnormalities disrupt normal neuronal architecture and connectivity, resulting in epilepsy, motor and cognitive impairment, as well as neuropsychiatric symptoms. In other organs, abnormal cell proliferation can lead to neoplastic lesions, such as renal angiomyolipomas, cardiac rhabdomyomas, and pulmonary lymphangioleiomyomatosis.
Clinical Manifestations
The clinical manifestations are highly variable. Neurological symptoms are prominent and include epileptic seizures such as infantile spasms, motor deficit, intellectual disability, and neuropsychiatric disorders. Cortical tubers and other brain lesions are the underlying pathology that causes these symptoms. Cutaneous changes are considered early manifestations and include hypomelanotic macules (“ash leaf spots”), facial angiofibromas, shagreen patches, and ungual fibromas. Renal involvement, such as angiomyolipomas, may lead to hematuria, hypertension, or renal impairment. Cardiac rhabdomyomas are frequently present in infancy and may even be detected prenatally. Pulmonary involvement, especially lymphangioleiomyomatosis, occurs more commonly in adult females and can cause progressive respiratory failure.
Neuropsychiatric manifestations, referred to as TSC-associated neuropsychiatric disorders (TAND), include behavioral abnormalities, anxiety, depression, and cognitive difficulties. The symptoms can occur at birth, during infancy, or later in life, depending on the involved organ and progression. Nevertheless, some patients remain undiagnosed or exhibit only mild symptoms due to reduced gene expression and variable penetrance.
Diagnosis
The diagnosis of TSC is based on major and minor criteria and genetic verification. The characteristic major and minor features, such as cortical tubers, facial angiofibromas, and renal angiomyolipomas, support the diagnosis. Brain MRI typically reveals cortical tubers, subependymal nodules, and possibly SEGAs (subependymal giant cell astrocytomas). Renal imaging (ultrasound or MRI) and cardiac evaluation (echocardiography) are two important methods for detecting multiorgan involvement.
Genetic analysis confirms the diagnosis by identifying pathogenic variants in TSC1 or TSC2, although not all individuals with clinical TSC have identifiable mutations.
Treatment
There is no curative treatment for TSC, and its management is multidisciplinary. It is focused on the patient's manifestations and functional deficits. Seizure control is a primary challenge and includes antiepileptic drugs, ketogenic diet, or epilepsy surgery in refractory cases. mTOR inhibitors, such as Everolimus, are an important therapeutic option and can reduce the size of SEGAs and renal angiomyolipomas, as well as improve some neurological and dermatological features. This includes neuroimaging, renal assessment, cardiac evaluation, and pulmonary function test. Dermatological treatments, including laser therapy, may improve cosmetic concerns. Supportive care, including neuropsychological assessment, behavioral interventions, and educational support, is crucial for TSC-associated neuropsychiatric disorders (TAND) and improving long-term outcomes.
Prognosis
The prognosis of TSC varies widely depending on the severity of organ involvement, particularly CNS involvement. Individuals with mild disease may have a near-normal life expectancy, while those with severe epilepsy, intellectual disability, or significant organ involvement experience a higher rate of morbidity. The possibility of early diagnosis and advances in new therapies, particularly mTOR inhibitors, can improve outcomes and quality of life. Regular and permanent monitoring is required due to the risk of tumor growth and progression of systemic manifestations.
