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SMA carrier:
common in every ancestry.

About 1 in 40 to 1 in 70 people carries spinal muscular atrophy (SMA), whatever their background. Here's what that means for your children and how carrier testing works.

By the DontMarryYourBro team · Updated October 2026 · 5 min read · How we fact-check

The short answer

  • SMA is a recessive condition that weakens the muscles. It was once the leading genetic cause of infant death.
  • Carriers are common in every ancestry: about 1 in 47 white, 1 in 52 South Asian, 1 in 59 East Asian, 1 in 68 Hispanic and 1 in 72 Black people.
  • If both partners carry it, each pregnancy has a 1 in 4 chance of SMA.
  • ACOG recommends offering SMA carrier screening to everyone who is pregnant or planning a pregnancy.

What SMA is

Spinal muscular atrophy (SMA) is caused by a missing or altered SMN1 gene. It affects the nerve cells that control muscles, leading to weakness that can affect moving, breathing and swallowing. The most severe type starts in infancy. Treatments approved since 2016, including a one-time gene therapy, have changed outcomes for many children, especially when started early, but SMA remains a serious condition.

Carrier odds by ancestry

AncestryChance of being an SMA carrier
Whiteabout 1 in 47
South Asian (Asian Indian)about 1 in 52
East Asianabout 1 in 59
Ashkenazi Jewishabout 1 in 67
Hispanicabout 1 in 68
Black / African Americanabout 1 in 72

Unlike many conditions, SMA is common across every ancestry, which is why guidelines recommend offering the test to everyone. Check your couple in the carrier odds calculator.

If both partners are carriers

Each pregnancy has a 1 in 4 chance of SMA. A genetic counselor explains options, including IVF with embryo testing and testing during pregnancy. If a baby does have SMA, early diagnosis matters, because treatment works best when started early.

How SMA carrier testing works

The test counts how many copies of the SMN1 gene you have. Most carriers have one copy instead of two. Some carriers have two copies on the same chromosome and none on the other, which the standard test can't see, so a normal result lowers your risk a lot without making it zero. The test misses more carriers of African ancestry for this reason.

General information, not medical advice.

Sources

  1. Sugarman EA et al. Pan-ethnic carrier screening and prenatal diagnosis for spinal muscular atrophy. Eur J Hum Genet (2012)
  2. ACOG Committee Opinion 691: Carrier screening for genetic conditions (2017)
  3. Gregg AR et al. Screening for autosomal recessive and X-linked conditions: ACMG practice resource. Genetics in Medicine (2021)
  4. Cure SMA: About spinal muscular atrophy

Two healthy people. One test.

The carrier check screens both of you for hundreds of recessive conditions at once, with a genetic counselor to explain the result as a couple.

Check our carriers

Questions people ask.

How common are SMA carriers?

About 1 in 40 to 1 in 70 people, depending on ancestry: roughly 1 in 47 white, 1 in 52 South Asian, 1 in 59 East Asian, 1 in 68 Hispanic and 1 in 72 Black people.

What if both parents are SMA carriers?

Each pregnancy has a 1 in 4 chance of a child with spinal muscular atrophy, a 2 in 4 chance of a carrier child, and a 1 in 4 chance of neither.

Can an SMA carrier test be wrong?

A normal result greatly lowers the chance you are a carrier but cannot rule it out completely. Some carriers have both SMN1 copies on one chromosome, which the standard copy-number test cannot detect.

Who should get SMA carrier screening?

ACOG recommends offering SMA carrier screening to everyone who is pregnant or planning a pregnancy, because carriers are common in every ancestry.