My husband and I conceived our second child just four months after we lost our first child to spinal muscular atrophy.
The decision to try to have a baby so soon after our son Andy’s passing was a difficult one. However, we hated being “childless parents” and felt ready to introduce another life to our family. After weighing all of our options, we conceived the baby naturally, and we prayed that the odds would be in our favor this time. It was assumed that, since there was no question about Andy’s SMA diagnosis, both my husband and I were carriers of the inherited gene that causes the disease, which gave us a one in four chance of having another SMA-affected child.
We had to wait until I was 12 weeks pregnant with our second child before the pre-natal testing for SMA could be done and three additional weeks for the test results. It was an excruciatingly stressful and long wait. As a condition of the pre-natal testing, my husband and I also had to have blood tests to determine our carrier status.
What the blood test does is count the number of the Survivor Motor Neuron 1 or SMN1 genes a person has. Typically, non-carriers have two copies of this gene, one passed from their mother and one from their father. SMA carriers have only one copy of the SMN1 gene, and their other gene is deleted. When two carriers each pass that deletion to their child, the child’s carrier test will show that he/she does not have any copies of the SMN1 gene at all and will confirm the diagnosis of SMA.
So we were surprised to receive the result that, while I definitely was an SMA carrier with one copy of SMN1, my husband appeared to not be a carrier at all or have any type of mutated gene that would cause the disease. His test showed that he had two copies of SMN1. We also learned that the new baby, a girl, was an SMA carrier like me, and would be unaffected by the disease. While we celebrated the health of our daughter Lucy, we were left with many questions. The most pressing being that, if my husband wasn’t a carrier, how did Andy have SMA?
Our geneticist gave us two potential answers. Either my husband WAS NOT a carrier, and the gene he passed to Andy mutated upon conception (called a “de novo” mutation), or he WAS a “hidden” SMA carrier with a genotype that the blood test could not detect. She said that de novo mutations have occurred in a small percentage (approximately 2-3 percent) of the population of people diagnosed with SMA. Also, she explained that there is a subset of approximately 6 percent of carriers that can not be identified by the current blood test.
In order to find out more, our family recently participated in what is called a “Linkage Study.” Blood samples were taken from each of our parents, my husband’s siblings, each of us, and Lucy to determine who passed what gene to whom. Luckily, we had Andy’s cord blood stored as well, so we could get a complete picture of how the SMA-causing deleted gene had traveled through our family to him. Scientists at the University of Pennsylvania conducted the study.
We received the results yesterday, learning that my husband is indeed a carrier of SMA. In his case, he received two copies of the SMN1 gene from one parent, and a deletion of the gene from the other. It is that deletion that both he and I passed on to our son.
So why am I sharing this story with you? Because if we’d had carrier testing before we had children, the test results would have indicated that my husband wasn’t a carrier – that he was “normal.” I would bet that the doctor explaining those results to us would have said that, even though I was a carrier, we had nothing to worry about. AND WE STILL WOULD HAVE UNKNOWINGLY HAD A CHILD WITH SMA.
It is critical to understand that the SMA carrier test, while very important, is not 100 percent accurate. If you received a “normal” result from an SMA carrier test, but it is confirmed that your partner is a carrier, there still is a possibility that you might have a child with SMA. That said, we are recommending that everyone in our family who plans to have children test for their carrier status. And, if any of them are carriers – regardless of their partners’ test results – that they also elect to have pre-natal testing done with any pregnancy.
This piece of knowledge is Andy’s gift to us all.
For more information on SMA carrier or pre-natal testing:
- Counsyl (saliva test): http://counsyl.com/
- Athena Diagnostics (blood test): http://www.athenasmaawareness.com
- LabCorp (blood test): http://www.labcorp.com
- Claire Altman Heine Foundation: http://www.clairealtmanheinefoundation.org/index.as
- UMass Lab Updates Newsletter (a very scientific explanation of SMA carrier testing results is on pages 3 and 4): http://www.umassmemoriallabs.org/assets/lab%20updates%20dec%202011.pdf