Spinal muscular atrophy (SMA) is a neuromuscular disorder that has no cure. People with a family history of SMA may consider screening to learn whether they carry the gene that causes the condition.
Spinal muscular atrophy (SMA) is a rare genetic condition that affects the nerves within the spine. This condition must be passed on by both parents during conception for a person to have the disorder. If only one gene is inherited, a person is considered a carrier.
Here’s more about what causes SMA, what it means to be a carrier, and what screenings are available to determine your carrier status.
SMA is inherited in an autosomal recessive pattern. This means that for a person to have the disorder, they must inherit two copies of affected genes (SMN1) – one from each parent – during conception.
A person who inherits only one affected gene is considered a carrier. A carrier does not have symptoms of the disorder but can pass the SMA gene to their offspring.
Between 1 in 40 and 1 in 60 people are carriers of the SMA. Being a carrier does not cause any outward signs. Instead, you’ll need to be screened for the gene.
Genetic testing can be done through a simple blood test. Your blood will be sent to a laboratory to look for the gene.
Results:
- If your screening shows that you have two unaffected copies of the gene, you are considered low risk for being a carrier.
- If your screening shows only one unaffected gene, you are considered a carrier. You could pass on an SMN1 gene to your offspring.
If you are a carrier of the gene, it does not mean that your personal health will be impacted. Instead, you may be referred to a genetic counselor to discuss the implications of being a carrier if you choose to have children.
There are several scenarios for the inheritance of SMA:
- You are a carrier, and your partner is not a carrier: You may pass on one copy of the gene, but your risk of having a child with SMA is low.
- You are a carrier, and your partner is also a carrier:
You may choose to be screened for SMA if you have a family history of the disorder or if you have previously had a child with the disorder.
Experts also recommend that individuals who are pregnant or looking to become pregnant be offered screening for SMA and other genetic disorders.
You may choose to be screened for SMA at any time. Some individuals choose to have screening before pregnancy or during pregnancy to learn of possible effects on their future children.
If you are already pregnant, your doctor will offer you prenatal testing – amniocentesis or chorionic villus sampling (CVS) – to determine the SMA status of your unborn child.
Before pregnancy, options include:
Some couples may choose not to have children or to adopt children to avoid passing on the affected SMN1 gene.
My family member has spinal muscular atrophy. Does this increase my risk of having a child with the disorder?
Yes. If you have a blood relative with SMA, there is a possibility you are a carrier and may pass the gene to your child.
Can carrier testing harm my unborn child?
No. A blood test does not pose any danger to a developing fetus.
Who can see my screening results?
Your results are confidential and cannot be released without your permission.
Screening for the SMN1 gene is an easy, relatively noninvasive process. If you test positive, you may work with a genetic counselor to determine the next steps should you choose to have children. If you are already pregnant and discovering your carrier status, your doctor can also offer testing to determine the status of your child.
There are various options depending on your circumstances. Your doctor can suggest options for pregnancy, refer you to local SMA resources, and point you to groups for additional support.