What is SMA

Spinal Muscular Atrophy is a condition characterized by muscle weakness and wasting that can start from before birth or all the way into adulthood. In the most severe cases, there can be decreased fetal movement during pregnancy and severely poor muscle tone is apparent at birth which can lead to joint contractures, respiratory failure, and in some cases, death within a few weeks or months. Intermediate forms of the condition may have later onset and varying degrees of motor delays and muscle weakness with variable lifespans. The most mild form is the most rare, and consists of adult onset muscle weakness. 

What Causes SMA

Most commonly, SMA is caused by deletions within a gene called SMN1. The disease is inherited in an autosomal recessive pattern which means that both of someone’s two copies of the gene need to be impacted for someone to have symptoms. 

Who’s at Risk for SMA

About 1 in 40 people are carriers of SMA - because carriers typically don’t have any symptoms, many people who are carriers of this condition have never heard of SMA before. If you have a known family history of the condition, your risk is likely higher. 

Most carriers of SMA have a deletion in one of their genes on one chromosome, but a fully functional gene on the other chromosome. Approximately 4% of SMA carriers are called “silent carriers” and carry two copies of the gene on one chromosome and none on the other (called a 2+0 carrier). Silent carriers may be at  risk for an affected offspring if their partner is a confirmed or silent carrier.

How Do I Know if I’m at Risk for SMA 

Spinal Muscular Atrophy is included on most standard carrier screens (genetic tests designed to identify reproductive risks). It's important to note that your risk for SMA depends not only on your carrier status but also on your partner’s/donor’s carrier status. Talk to your IVF provider or OB/GYN to learn more about how you can access carrier screening. 

My partner/donor and I are Both Carriers - What’s my Risk for Having a Child with SMA  

If you and your partner/donor are both confirmed carriers of Spinal Muscular Atrophy, there is a 25% risk for each embryo/pregnancy to inherit both of your deleted copies of the SMN1 gene. 

If you and/or your partner/donor are silent carriers there is up to a 25% risk for each embryo/pregnancy to be affected. This is because current technology cannot definitively distinguish between non-carriers (1 gene on each chromosome) and silent carriers (2+0) but instead looks at markers to identify people at a higher risk for silent carrier status. This risk is typically dependent on ancestry - check your carrier screening results for your specific risk. 

Is Embryo Screening for SMA Available

Yes! Orchid’s whole genome embryo screening provides a simplified option for targeted SMN1 screening for families known to be at risk for Spinal Muscular Atrophy. While historically silent carriers often had no way to screen embryos for SMA, Orchid’s screening is available for confirmed carrier couples and those with silent carrier risk. By providing direct testing for SMN1 gene copy number, this screening distinguishes embryos with zero copies (affected) from those with one or more (unaffected)*, allowing you to prioritize embryos with the lowest risk for SMA. 

*Please note, sequence variants will not be reported and ~2% of SMA cases are the result of de novo pathogenic variants not screened for by Orchid’s PGT-M for SMA. Orchid’s PGT-M for SMA does not distinguish between carriers and non-carriers. 

How Does Orchid’s SMA Testing Differ from Traditional PGT-M 

• No family member testing or saliva samples required (aside from egg and sperm source)
• No custom probe development = faster timeline to results and streamlined process
• Simultaneous comprehensive reporting of other clinically significant conditions 

Ready to Get Started

Reach our board-certified genetic counselors at genetics@orchidhealth.com with a copy of your SMA carrier screening results and they’ll advise on next steps to get set up! 

REFERENCES: 

Prior TW, Leach ME, Finanger EL. Spinal Muscular Atrophy. 2000 Feb 24 [Updated 2024 Sep 19]. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1352/

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