Rare Genetic Motor Neuron Disease Treated In Womb For The First Time

SMA is a progressive condition that affects motor neurons, the specialized cells that control voluntary muscle movement. It has five subtypes, of which type 1 is considered to be the most severe; people with this form have a mutation in both copies of a gene called SMN1, which encodes a protein called SMN that enables muscles to receive nerve signals.

Without this protein, muscles can’t function normally, and so they weaken and waste away over time. In individuals with SMA type 1, this typically leads to symptoms within the first six months of life, and without treatment, they are likely to die before the age of two. 

While there’s currently no cure for SMA, there are treatments. They usually target a neighboring gene, SMN2, which also produces the SMN protein. Until now, however, such treatments had only ever been given after birth, although genetic testing can diagnose the condition during pregnancy.

Physicians at St. Jude Children’s Research Hospital in Tennessee have just changed that. They were treating an expectant mother who had previously lost a child to SMA type 1, and was pregnant again with a fetus found to be highly likely to have the disease.

After the parents wanted to know if there were treatments for SMA that could be given before birth, the team sought FDA approval to trial a drug called risdiplam – and they were given it.

During the last six weeks of pregnancy – a time when the SMN protein is most needed in fetal development – the mother received a daily oral dose of risdiplam and was monitored for any side effects, while the team also closely followed the fetus’ growth and development.

After the baby was born, it was given the drug directly. As of February 2025, the child is now 30 months old and has continued to receive risdiplam and periodic monitoring for any SMA symptoms – none have appeared.

“During the course of the assessment, we really have seen no indication of any signs of SMA,” said Richard Finkel, MD, St. Jude Center for Experimental Neurotherapeutics director and Department of Pediatric Medicine member, who is the corresponding author of an article detailing the case, in a statement.

The child was born with some congenital abnormalities, but these were determined to have occurred before the risdiplam was given.

While this is just one case, those involved are hopeful that it could be enough to support future research into treating SMA in this way.

“Our primary objectives were feasibility, safety and tolerability, so we’re very pleased to see that the parent and child are doing well,” said Finkel. “The results suggest it would be worthwhile to continue investigating the use of prenatal intervention for SMA.”

The study is published in the New England Journal of Medicine.