A genetic counselor 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.
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.
Genetic testing is recommended for anyone diagnosed with or suspected of having TSC, as well as for all immediate family members if the individual's mutation has been identified. Although the test is not currently used to diagnose TSC, it is often used to confirm a clinical diagnosis. Mutations that cause TSC may be found anywhere on the two genes—TSC1 and TSC2—associated with the disorder. In fact, in approximately 15 percent of people diagnosed with TSC, a mutation is never found. However, once a particular mutation is located for someone clinically diagnosed with the disorder, examining the DNA of family members for that specific mutation is relatively simple.
Geneticists expect that in the future, genetic testing will be able to tell us far more than it can today about our risk of disease. Someday soon, tests will likely be sensitive enough to screen the general public for a wide array of genetic disorders, including TSC. This will ultimately help people who are mildly affected by TSC know they have the disease and make informed reproductive decisions in the future. Currently, however, doctors do not recommend that the general public with no pre-existing risk factors for TSC undergo genetic screening for the TSC mutation.
Another goal of current research into TSC is to explain why some people with TSC are severely affected while others are only mildly affected. Researchers hope to find a genetic cause to explain the variability. If they can do this, they may be better able to predict the problems an individual will encounter by looking at his or her genes.
It is important to remember:
- Physicians who specialize in TSC routinely refer recently diagnosed individuals and family members to genetic counselors.
- Genetic counseling is one of the best ways of gaining knowledge about TSC, especially as it relates to a particular family.
- Genetic counselors help family members determine where and when a TSC mutation arose in their family.
- Genetic counselors help parents understand that they could not have caused or prevented TSC in their child.
- Most people with TSC and their immediate family members undergo complete physical examinations and genetic testing as a part of genetic counseling.
- Genetic counselors help adults who have TSC understand the risk of passing their mutation on to their children.
- Genetic counselors inform families affected by TSC of the options available to them regarding reproduction and other health decisions.
- Most genetic counselors provide families with a complete written report of their counseling sessions, to serve as an important medical reference in the future.
- Genetic counselors can also provide brochures and Web sites about the technical information that was discussed during the sessions.