THE GENETICS OF TSC

Tuberous sclerosis complex (TSC) can be inherited or it can occur randomly. In fact, about two-thirds Genetics Imageof TSC cases have no link to family history.

It’s important to understand how genes play a role in TSC, the value of genetic testing, and its potential impact on your family.

Tuberous sclerosis complex (TSC) can be inherited or it can occur randomly. In fact, about two-thirds of TSC cases have no link to family history.

It’s important to understand how genes play a role in TSC, the value of genetic testing, and its potential impact on your family.

Genetics Image
  • TSC is caused by a defect, called a mutation, in the genes that are responsible for producing 2 proteins—TSC1 (hamartin) and TSC2 (tuberin)
  • Both genes are believed to help control cell growth
  • The TSC2 gene mutation occurs in the majority of random cases (70% to 80%)
  • With extensive screening, the mutations that can cause this disease may be found in approximately 85% of people with TSC
  • The mutation can be passed down from a parent or it can develop on its own
  • Other differences between TSC1 gene mutations and TSC2 gene mutations are described in the chart below

TSC1 gene mutations (hamartin)

  • Twice as likely in family cases than in random cases
  • Mutations are identified in only 10% to 30% of TSC patients

TSC2 gene mutations (tuberin)

  • More prevalent in random cases than in family cases
  • Patients more likely to experience:
The Genes in TSC

EXPERT INSIGHT

The Genes in TSC

Comparing the differences between TSC1 and TSC2 genes

The Role of mTOR in TSC

  • mTOR, which stands for “mammalian target of rapamycin,” is an important factor that helps control the growth of cells in the body
  • Normally, genes called TSC1 and TSC2 work to control mTOR and cell growth
  • When these genes are defective—which is what happens when someone has TSC—they can’t do their job of controlling mTOR
  • When mTOR is not controlled correctly, cells can grow out of control and tumors can form throughout the body

TSC Can Run in the Family

TSC is as unique as the individual who has it—even within a family. For example, one family member may be mildly affected (with only a few physical symptoms, no seizures, and normal cognition). On the other hand, a sibling may experience severe mental disability, physical signs and symptoms, autism, and disruptive behaviors.

Passing TSC to Your Children

There is a 50% chance of an affected parent passing TSC on to their children. And both males and females are equally likely to have this disease. Even if parents of an affected child show no signs of TSC, they still have a chance of having other children with this condition.

The Value and Implications of Genetics in TSC

EXPERT INSIGHT

The Value and Implications of Genetics in TSC

Why genetic testing and counseling make sense for patients and families

The Value of Genetic Testing and Counseling in TSC

Genetic testing can provide further understanding if you have TSC. Genetic testing can:

  • Identify mutations in up to 75% to 90% of people who have TSC based on clinical criteria. (It’s important to note that a negative test result does NOT exclude a diagnosis of TSC)
  • Offer more knowledge in cases that are questionable based on physical evaluation alone
  • Provide more information to help with family planning
  • Screen family members of a person with TSC

Genetic counseling can provide more insight for those who have tested positive for inherited TSC. Also, speaking to a genetic counselor may provide useful information for those thinking about starting or expanding a family.

A genetic counselor may also help explain undiagnosed symptoms that affect other family members. When TSC is inherited, the source of the TSC can be traced back several generations.

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