On Feb. 19, 2025, scientists at St. Jude Children’s Research Hospital report results from a promising new approach to treat the rare neurodegenerative disorder.

Spinal muscular atrophy (SMA) is a progressive neurodegenerative disorder set in motion before birth. St. Jude Children’s researchers led the first in utero treatment of SMA with the orally administered drug risdiplam. More than two years after the child was born, no identifiable features of SMA have been observed. This study demonstrates the feasibility of treating SMA prenatally and supports further investigation into the approach.

SMA is caused by a lack of survival motor neuron protein and occurs in around 1 in every 11,000 births in the United States. If not treated, SMA type 1 (SMA-1), the most common and severe form, results in progressive muscle weakness that leads to death. Currently, treatments for SMA-1 have demonstrated improved survival and motor function in infants, especially if administered shortly after birth before symptoms begin, but is not a cure.

Shortly after birth, the infant was diagnosed with three developmental abnormalities: ventricular septal defect (which resolved), optic nerve hypoplasia and a brainstem asymmetry, with related delays in vision and overall development. These abnormalities are considered to have occurred early in fetal development before exposure to risdiplam. 

The parents in this case were both known carriers of SMA genetic variants and had a prior infant born with SMA-1 before current treatments became available, who died at 16 months of age. Genetic testing conducted by amniocentesis confirmed the fetus had no copies of the survival motor neuron gene, which, in combination with the family history and other genetic information, was highly predictive of the infant being born with SMA-1. Risdiplam was administered to the expectant mother during the final six weeks of pregnancy.

Shortly after birth, the infant was diagnosed with three developmental abnormalities: ventricular septal defect (which resolved), optic nerve hypoplasia and a brainstem asymmetry, with related delays in vision and overall development. These abnormalities are considered to have occurred early in fetal development before exposure to risdiplam. Now two-and-a-half years old, the child continues to be monitored periodically at St. Jude.