Q: My husband and I would never consider terminating a pregnancy. Why should we or couples who share our views consider SMA carrier testing?
A: While opposition to termination of a pregnancy is sometimes cited in arguments against genetic testing, it is important to realize that termination of a pregnancy is never the only option. There are many benefits to knowing the results of a prenatal genetic test because of all the reproductive options that parents can consider.
Q: Is carrier testing voluntary?
A: Yes, any type of genetic testing is entirely voluntary.
Q: Why is it important to meet with a genetic counselor when considering SMA carrier testing?
A: It is important that individuals undergoing SMA carrier testing understand that a carrier is a healthy person who is not at risk of developing SMA but has a risk of passing the responsible gene mutation onto his or her children. A genetic counselor or similarly knowledgeable medical professional, such as an obstetrician/gynecologist with genetic training, has the education and training to explain all the nuances of genetic testing and test results, including test limitations and options for couples who are identified as carriers.
Q: Is it possible to learn whether our baby has SMA before he or she is born?
A: Yes. Prenatal testing for SMA is done via chorionic villus sampling (CVS) or amniocentesis. The accuracy of prenatal tests is nearly 100%. Diagnostic testing (done by a blood test) is available after the baby is born.
Q: What is the importance of knowing the copy number of the SMN2 gene?
A: In approximately 98% of patients, SMA is associated with a mutation of the SMN1 gene. Yet several studies have shown that the copy number (from 0 to 5) of a nearly identical "back-up" gene, SMN2, influences the severity of the disorder. For example, patients with the milder type II or type III SMA (about 30% of patients) have been shown to have more copies of SMN2 (three or more) than patients with the more severe type I SMA.
Knowing the SMN2 copy number is important because it provides valuable information to parents about the prognosis of an affected fetus. For example, one scientist reported on an SMA patient with five copies of SMN2 who was a competitive skier in her teens and was still able to walk at age 50.
Q: If I am found to be an SMA carrier, is there any way we can be reassured that the results of my husband's test are 100% accurate so that we base our reproductive choices on correct information?
A. While SMA carrier testing has a very high detection rate, it does not detect all carriers (those with rare mutations), so it does not offer a 100% detection rate. Currently, carrier testing offers about a 90% detection rate.
Beginning in 2010, however, Athena Diagnostics will offer couples like you and your husband the "SMA Plus" test. This test is recommended in cases like yours, where an expectant woman has been found positive for SMA carrier status and the couple wants the added level of assurance about their results. The SMA Plus test, which can detect rare "point mutations," offers an increased detection rate (2-4%) for the spouse, increasing the detection rate to a total of approximately 92-94%.