A tuberous sclerosis complex (TSC) diagnosis prompts many questions. You will likely talk through many of your questions with various physicians, including primary care doctors and specialists. Another important resource is a genetic counselor, who can provide you with specialized information about TSC in a context that extends beyond clinical diagnosis and treatment.
Genetic counselors provide people who have TSC and their families with a deeper understanding about the genetics and inheritance of the disorder through accessible explanations and informative illustrations. They also help individuals understand TSC in the context of their particular family, determining who in the family may have the mutation and if a mutation has been passed from one individual to his or her children. With an understanding of the inheritance of TSC and information about various tests and options available to them, family members are better able to make informed health and reproductive decisions.
What to Expect
People often seek genetic counseling immediately following their own diagnosis or that of a family member. In some cases, however, a person diagnosed years prior may see a genetic counselor to learn more about the risk of passing TSC to offspring.
Because TSC is a genetic disorder, often genetic counseling involves an explanation of the basics of genetics—where chromosomes are located, where on chromosomes genes are found, what genes do, and how mutated genes can cause disease.
A straightforward approach to understanding the basics of genetics naturally leads to a discussion of the genetic causes of TSC. In a genetic counseling session, people learn that TSC is caused by a mutation of either the TSC1 gene on chromosome 9 or the TSC2 gene on chromosome 16. They learn that these mutations can arise spontaneously during gestation or can be passed from parent to child. They also learn that nothing done prior to or during pregnancy can cause or prevent a spontaneous TSC mutation.
Genetic counselors can help people affected by TSC understand the disorder in the context of their particular family by constructing a detailed medical history and pedigree of approximately three generations of family members.
TSC specialists recommend that all immediate family members of someone diagnosed with TSC and whose mutation has been identified undergo genetic testing to determine if they also have the mutation. Results from these tests and physical examinations help physicians, genetic counselors, and family members identify when and where TSC arose in the family and who might be affected, and helps family members assess the outcome of decisions they may make in the future.
Some people who seek information and advice from genetic counselors are young adults mildly affected by the disorder, who want to assess the risk of passing TSC to a child. They learn that a person with TSC has a 50 percent chance of passing their mutation to the next generation. They also learn that mildly affected parents do not necessarily have mildly affected children. Manifestations of the disorder can vary widely from one individual to another, causing one person to be severely affected while another is only mildly affected, even if they share the same TSC mutation. Experts still aren't sure why the disease has such unpredictable consequences. (For more information, see Cause.)
Genetic counselors help people with TSC make informed decisions in the event that they wish to become parents. Now, through prenatal genetic testing (amniocentesis or chorionic villi sampling), expectant parents can determine if an unborn child has inherited the same mutation as the parent or sibling who has already had a positive genetic test for TSC. This provides parents with important knowledge on which to base the difficult decision about whether to proceed with or terminate a pregnancy, or to help them better prepare for the arrival of a baby with TSC.
Another genetic test, called pre-implantation diagnosis, is available as part of most in vitro fertilization procedures. Lab technicians take several developing embryos, just days after fertilization, and extract one cell from each embryo. The DNA from each embryo is then screened for the family's known mutation. Then only those embryos that did not inherit the mutation are selected for placement into the mother's uterus. This technique does not affect the developing embryo and, although expensive, provides a high degree of assurance that a parent who has TSC will have a child who is free of the disorder.