Spinal muscular atrophy runs in my family, although I don't have it. If I have children, are they at risk?
It's possible, but to better understand the risk, both you and your partner need a DNA test.
Spinal muscular atrophy (SMA) — a group of diseases that damages certain nerve cells in the spinal cord — is genetic. This means it's passed on by parents. In the majority (95%) of people with SMA, the cause is an abnormal or missing survival motor neuron 1 (SMN1) gene.
Spinal muscular atrophy is an autosomal recessive genetic condition. This means that for a child to have the condition, the child must inherit two copies of the abnormal or missing gene — usually one from each parent.
If only one parent carries the abnormal or missing gene, the child likely isn't at risk of having SMA. But the child will have a 50% chance of inheriting one copy of the gene and becoming a carrier. This means that he or she might pass the abnormal gene on to future children.
Though very rare, it's possible for a spontaneous change in the SMN1 gene to occur in an egg or sperm. If that happens, a child could possibly have the condition, even if only one parent is a carrier.
To get a better picture of the risks, you and your partner can each get a DNA test to see if either of you carries the abnormal or missing SMN1 gene. About 1 in 50 people are carriers.
If you're both carriers of the abnormal or missing gene, your children will have a 25% chance of having SMA, a 50% chance of becoming carriers and a 25% chance of being unaffected.
Testing may miss about 10% of carriers across the general population and about 30% in the African American population.
Sept. 23, 2020
See more Expert Answers
- Carriers of SMA. Cure SMA. https://www.curesma.org/carriers-of-sma/. Accessed Aug. 25, 2020.
- Genetics. Cure SMA. https://www.curesma.org/genetics/. Accessed Aug. 25, 2020.
- Slide show: How genetic disorders are inherited. Mayo Clinic. https://www.mayoclinic.org/tests-procedures/genetic-testing/multimedia/genetic-disorders/sls-20076216. Accessed Aug. 25, 2020.
- Bodamer OA. Spinal muscular atrophy. https://www.uptodate.com/contents/search. Accessed Aug. 18, 2020.
- Sugarman EA, at al. Pan-ethnic carrier screening and prenatal diagnosis for spinal muscular atrophy: Clinical laboratory analysis of > 72,400 specimens. European Journal of Human Genetics. 2012; doi:10.1038/ejhg.2011.134.