On the Front Line of Life: Treatment of a Child in Utero

Until now, doctors have limited themselves to administering treatments after birth in an attempt to slow the progression of the disease.

For the first time, the Food and Drug Administration, the federal agency that issues approvals for the use of new treatments in the United States, has authorized a clinical protocol for in utero treatment on a fetus diagnosed with spinal muscular atrophy type 1, which in its most severe forms limits life expectancy to two years. The results, published in February 2025 in the New England Journal of Medicine, are very encouraging, even though the child being treated is now two and a half years old.

Type 1 spinal muscular atrophy, also known as infantile spinal muscular atrophy (SMA), or Werding-Hoffmann disease, is due to an abnormality in the SMN1 gene that leads to the absence of production of the survival motor neuron protein that control muscle movement, and their degeneration. As the muscles are less well innervated, they lose volume and strength.

The disease causes severe and progressive muscle weakness that most often begins within the first six months of life. In a press release, doctors from St. Jude’s Children’s Research Hospital in Memphis, Tennessee, emphasized that the earlier treatment is administered—before the first symptoms appear—the more likely children are to develop normally.

When doctors confirmed by amniocentesis that the fetus did not have any copies of the SMN1 gene, "which... indicated a very high risk that the infant would be born with type 1 SMA," at the request of the parents, who had already lost a child to this disease, in utero treatment with risdiplam was initiated.

The drug, administered to the mother, has the particularity of passing through the placenta to reach the fetus. It was given orally from the 32nd week of pregnancy until the child's birth at 38 weeks. Risdiplam was then administered directly to the child eight days after birth and until the child was 30 months old.

To date, no symptoms of spinal muscular atrophy, such as muscle weakness, lack of reflexes, or breathing difficulties, have been observed in the two-and-a-half-year-old child. Although this treatment, carried out on a single case of spinal muscular atrophy, still needs to be studied more widely, it constitutes an encouraging avenue for the in utero treatment of type 1 spinal muscular atrophy.