The first time I heard the words “Spinal Muscular Atrophy,” my infant son Andy was being diagnosed with one of the most severe forms of the degenerative disease. My husband and I were shocked to learn about SMA and that we, apparently, were silent carriers of this killer. Our parents were equally shocked. How could it be that none of us had ever heard about the leading inherited cause of death in young children?
We scoured our family history on all sides, looking for other incidences of SMA and only finding dead ends. We understood that SMA is an autosomal recessive disease, which means that two copies of the abnormal gene must be present in order for the disease to develop. We knew that this insidious SMA-causing gene was hiding in the DNA of our family, secretly passed down from carrier to carrier and from generation to generation. And, we were on a quest to find it.
So, my husband and I began talking to our relatives on every side of the family – sisters, brothers, nieces, nephews, cousins, aunts, and uncles – about the importance of SMA carrier testing. We wanted to spread awareness about SMA and, hopefully, stop our loved ones from having to experience it for themselves.
While the great majority of our family members understood why we were asking them to consider testing, in some unfortunate cases, our efforts were met with skepticism, indifference, or even rejection. And, as disheartening as these reactions were to us, they are not entirely unreasonable. All of this talk of genetics can be confusing, statistics can be misleading, and denial is a strong emotion. No one wants to be a carrier of SMA. No one wants to believe that SMA could impact their children. It’s easier to think that someone else or some other branch of the family tree is to blame for this errant gene. If the odds are that one in every 40 people is a carrier – and my husband and I were definitely carriers – then they couldn’t be too, right? It happened to us, so they were safe, right?
But, here’s the problem – that’s not how the statistics really work. Those statements are just not true.
While the carrier rate for SMA in the general population, crossing all ethnicities, is one in 40 people, carrier rates for specific ethnicities vary. For Caucasians, like our family, the carrier rate is higher than average. Even more important, when an SMA-affected person is one of your relatives, the carrier rate rises exponentially.
Here are the actual statistics if your family has a history of SMA:
- If your brother or sister has SMA, you have a 2 in 3 chance of being a carrier.
- If your niece or nephew has SMA, you have a 1 in 2 chance of being a carrier.
- If you have an aunt or uncle with SMA, you have a 1 in 3 chance of being a carrier.
- If your cousin has SMA, you have a 1 in 4 chance of being a carrier.
Our family’s test results prove these real-world statistics. In the four years since Andy was diagnosed with SMA, 12 family members, including aunts, uncles, cousins, nieces, nephews, parents, and siblings, have undergone carrier testing. Of those 12, eight are proven carriers, two are non-carriers, and two had inconclusive results (but at least one of them is an assumed carrier). That means that at least two out of every three blood relatives tested were, in fact, carriers of SMA.
And, as we delved further into testing, we learned even more about just how prevalent the disease really is.
In 2011, our immediate family underwent a linkage study to try to determine how the SMA-causing gene traveled to Andy. (You can read more about that study here.) While the study confirmed my husband’s and my carrier statuses and clarified how the gene was passed down on my husband’s side of the family, the test results for my parents were inconclusive. It was assumed that at least one of my parents was a carrier – since someone had to pass the defective gene to me – but we didn’t know who it was or where the gene came from.
Again, we moved forward, telling both my mother and father’s sides of the family to get SMA carrier testing if they planned to have children. As a result, we have found carriers on BOTH sides, surprising many of my family members. This shows, once again, that SMA is more common – and more elusive – than you think. And, how you interpret the results of carrier testing is critically important as well. Consider this:
Had my mother been ruled out during the linkage study as a carrier, would the relatives on her side of the family have asked for testing? My guess is that they would have felt spared from the risk of SMA, so why seek testing for it? And, they never would have learned that they, in fact, were carriers too.
The same can be said for my father. Had his carrier test come back negative for SMA, would his side of the family elected for testing? Most likely not. Again, blinded by a sense of false security, another carrier potentially would have gone unidentified.
Or, it may be that both my mother and my father are carriers, and I am lucky to not have the disease myself. With doctors and insurance companies telling us that there is “no medical necessity” for further testing for my parents, we may never know.
While it is frustrating that we can’t trace where the gene originated, it really doesn’t matter – the bottom line remains the same. The gene is here now, and the danger of SMA occurring again is real.
And, for all of the questions that carrier testing has raised, it also has provided some very meaningful answers. We now have confirmed that the disease can be found in all branches of our family. We have been astonished by the amount of carriers identified so far and know how vital testing for other relatives is. Most importantly, we now have more knowledge about SMA for future generations of our family – knowledge which is critical in preventing another loss to the disease.
So, what’s the moral of this story? If you know that you are related to someone with SMA and you plan to have children, please elect for carrier testing prior to pregnancy. Even if you believe that the gene is on a different side of your family, if you’ve already had healthy children, or if there’s no way you could be a carrier – you might be surprised. I know my family was.
I’m very proud of those who have been tested for facing the reality of SMA. I know how scary it is to find out that you are a carrier of such a horrific disease. But, I also know how much more devastating it is to lose a child to it.
For more information on SMA carrier testing, please visit these links:
- 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
— Audra Butler