FAQs on inheritance

 

 

 

 

Q: I am living with SMA. And I am thinking of having a child. 
A: Please contact your doctor or genetic counselor. In case, your partner is not a carrier then the risk for your child to be born with SMA is minimal (0% but there is always the risk of a spontaneous mutation) but the child will be a carrier. In case, your partner is a carrier then the risk of the child to be born with SMA is 50% and 50% of being a carrier. 

Q: My partner is a carrier of SMA and we are thinking of having children. Where can I get tested to see if I am a carrier too?
A: Ask your doctor to refer you to your regional genetics centre. The main genetics clinics are usually in large regional cities, but outreach clinics may be held in other smaller hospitals across the region.

Q: In a family with SMA who will be able to have genetic testing?
A: Staff at your regional genetics centre can give you specific advice about who might need to be tested. Close family members will be seen first to identify who might be carriers. The process might include drawing a family tree.

Q: There is a history of SMA in my family, when should my partner and I have genetic testing?
A: Having genetic counselling before pregnancy will give you and your partner more time to think about genetic testing and the possibly difficult decisions this can raise. But, do not be afraid to seek genetic counselling if you are already pregnant.

Q: I have been tested for SMA and the test has come back negative, but my doctor still thinks I have SMA. Is this possible?
A: In a small number of cases the genetic basis is more complex and further genetic testing may be necessary. Your doctor will advise you depending on your symptoms and the tests you have had so far.

Q: My son has SMA symptoms but the test has come back negative. Is it possible that he has SMA? 
A: Routine testing for SMA will confirm the diagnosis in the majority of people, but sometimes further genetic testing may be needed. Your doctor will advise you depending on your son’s symptoms and the tests he has had so far. This may include investigations for other conditions that can present in a similar way to SMA.

Q: My daughter has been diagnosed with SMA. I’m worried that her brother and sister might develop SMA too. Should they be tested?
A: It is important for you to discuss this with the healthcare professionals involved and your family. Your decision may be influenced by the type of SMA your daughter has and whether you already have worries about the health of your other children.

Q: My sister’s son has been diagnosed with SMA. I have a 4 year old daughter and I’m worried that she might develop SMA too. Should I have her tested?
A: You could have carrier testing at a genetic centre to see whether or not your children have a chance of having SMA. Once you have this result you can discuss with your healthcare professionals and your family whether or not to test your daughter. Genetic centres would not usually offer carrier testing in childhood as it removes the child’s right to make an informed decision when they are older.

Q: is there an overview for the different situations?
A: For each pregnancy (if inherited and not de novo), here are the possible outcomes:

If both parents are carriers:

  • Child won't have SMA and will NOT be a carrier: 1 in 4 (25%)
  • Child won't have SMA but will be a carrier: 2 in 4 (50%)
  • Child will have SMA: 1 in 4 (25%)

1 parent is a carrier, the other does NOT have SMA and is NOT a carrier:

  • Child will NOT have SMA
  • Child will NOT have SMA and will NOT be a carrier: 2 in 4 (50%)
  • Child will NOT have SMA and will be a carrier: 2 in 4 chances (50%)

1 parent has SMA, the other does NOT have SMA and is NOT a carrier:

  • Child will NOT have SMA
  • Child will be a carrier: 4 in 4 chances (100%)

1 parent has SMA, the other is a carrier:

  • Child will have SMA: 2 in 4 chances (50%)
  • Child will be a carrier: 2 in 4 chances (50%)

Both parents have SMA:

  • All children will have SMA: 4 in 4 chances (100%)