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.

With

Duygu Selcen, M.D.

Sept. 23, 2020 See more Expert Answers