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Tuberous Sclerosis Complex

Tuberous Sclerosis Complex is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • Tuberous sclerosis complex (TSC) is a genetic neurocutaneous syndrome (phakomatosis).
  • Classic triad: intellectual disability, facial angiofibromas, and seizures; multiple hamartomas
  • System(s) affected: nervous, skin, renal/urologic, pulmonary, cardiovascular, musculoskeletal, ophthalmologic, exocrine
  • Synonym(s): Bourneville disease

Pregnancy Considerations
Prenatal diagnosis by mutational analysis is possible when a familial mutation has been identified.

Epidemiology

Incidence
  • 6.8 to 12.4/10,000 live births (1)
  • Predominant age: Clinical expression is variable; usually is diagnosed during the 1st decade of life
  • No gender predominance

Etiology and Pathophysiology

  • Mutations in either of two genes—TSC1 and TSC2—that code for hamartin and tuberin, respectively. These form a heterodimer that acts as a tumor suppressor.
  • Decreased production of TSC proteins and excessive cell proliferation results in tuber formation.
  • Loss of gene function is associated with hyperactivity of the mechanistic target of rapamycin complex 1 (mTORC1) signaling.
  • In TSC, some hamartomas show loss of heterozygosity on chromosome 9q34.13 or 16p13.3.
    • The patient has inherited a mutation or a deletion in one copy of the gene but develops a lesion only when there is a somatic mutation in the other.
    • This two-hit mechanism explains the variable expressivity and seems to apply to cardiac rhabdomyomas, renal angiomyolipomas, and subependymal giant cell tumors (SGCTs) but not to cerebral tubers.

Genetics
  • Autosomal dominant with complete penetrance and variable expressivity (OMIM 191100 and 191092)
  • 2/3 of cases result from new mutations. Somatic mosaicism occurs in 2–10% of de novo TSC.
  • Two chromosomal loci: TSC1 (9q34.13); TSC2 (16p13.3) (TSC2 3 times as common as TSC1)
  • Genetic testing is recommended when TSC is suspected but not clinically confirmed (2)[C] and for all new patients with TSC (1)[C].
  • Clinical phenotype of TSC1 mutations generally is milder than that of TSC2 mutations (3).
  • There is a contiguous gene deletion involving large deletions and rearrangements of TSC2 and PKD1 (causing polycystic kidney disease).

Risk Factors

  • Family history. Expressivity is variable, even within a family.
  • If neither parent of an affected child meets criteria for TSC, the recurrence risk is 1–2% per child.

General Prevention

Genetic counseling

Commonly Associated Conditions

  • Intellectual disability (55–70%): usually associated with history of seizures, autism (40–50%)
  • Cortical tubers 82%, subependymal nodules (78%), subependymal giant cell astrocytomas (SEGAs) (24%)
  • Seizures (83%), 78% of whom diagnosed ≤2 years old
  • 25% of patients with infantile spasms have TSC.
  • TAND: interrelated functional and clinical manifestations of brain dysfunction common in TSC: aggressive behaviors, autism spectrum disorders, intellectual disabilities, psychiatric disorders, neuropsychological deficits, and school and occupational difficulties (1,2)
  • Cardiac rhabdomyomas (34–67%)
  • Lymphangioleiomyomatosis (LAM) of the lung, especially in women (up to 80%) (4)
  • Cardiac arrhythmias
  • Renal insufficiency, renal angiomyolipomas
  • Retinal lesions: hamartomas (up to 75%), achromic patches (39%)

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Citation

Stephens, Mark B., et al., editors. "Tuberous Sclerosis Complex." 5-Minute Clinical Consult, 27th ed., Wolters Kluwer, 2019. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116624/2.0/Tuberous_Sclerosis_Complex.
Tuberous Sclerosis Complex. In: Stephens MB, Golding J, Baldor RA, et al, eds. 5-Minute Clinical Consult. 27th ed. Wolters Kluwer; 2019. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116624/2.0/Tuberous_Sclerosis_Complex. Accessed July 22, 2019.
Tuberous Sclerosis Complex. (2019). In Stephens, M. B., Golding, J., Baldor, R. A., & Domino, F. J. (Eds.), 5-Minute Clinical Consult. Available from https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116624/2.0/Tuberous_Sclerosis_Complex
Tuberous Sclerosis Complex [Internet]. In: Stephens MB, Golding J, Baldor RA, Domino FJ, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2019. [cited 2019 July 22]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116624/2.0/Tuberous_Sclerosis_Complex.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Tuberous Sclerosis Complex ID - 116624 ED - Stephens,Mark B, ED - Golding,Jeremy, ED - Baldor,Robert A, ED - Domino,Frank J, BT - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116624/2.0/Tuberous_Sclerosis_Complex PB - Wolters Kluwer ET - 27 DB - Medicine Central DP - Unbound Medicine ER -