Every year it seems like more and more genetic tests are offered during pregnancy. Due to a recent recommendation made by the American College of Medical Genetics (ACMG), the latest carrier test to be offered by OB/GYNs and genetic specialists is for spinal muscular atrophy (SMA).
What is SMA?
The number 1 inherited cause of childhood death, spinal muscular atrophy is a group of devastating genetic disorders that affect muscle movement and cause muscle degeneration and weakness. SMA is divided into types (SMA Type 0 – SMA Type IV) based on symptom severity and the age of symptom onset.
How is SMA inherited?
SMA has autosomal recessive inheritance, which means that two alterations, one in each gene copy, are necessary to cause the disorder. People with only one mutated copy are called carriers. Two carriers have a 25% chance to have an affected child, but do not typically have symptoms themselves. As such, carriers of SMA may not know they have a mutation until they have an affected child.
What is your chance to have an affected child?
A family history of SMA can significantly increase your chance to be a carrier.
For example, if you have a sibling who is a carrier of SMA, you have a 50% chance to also be a carrier. If you have a first cousin who is affected with SMA, you have a 25% chance to be a carrier. If you have a child with SMA, you and your partner have a 100% chance to both be carriers, and a 25% chance to have another affected child.
Even if you have NO family history of SMA, you can still be a carrier.
In the absence of a family history, the risk of being a carrier is based on your ethnic background, as SMA is more common in people of certain ethnic backgrounds.
Understanding your risk is the first step to making an informed decision about carrier testing. To better understand your personal risk, you can use our Family Health History tool to assess the risk for SMA in addition to over 200 other hereditary diseases.