Spinal Muscular Atrophy Treated in the Womb for the First Time

Spinal muscular atrophy (SMA) is a progressive neurodegenerative disorder set in motion before birth. Scientists at St. Jude Children’s Research Hospital 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. The findings were published today in a letter to the New England Journal of Medicine.

“Our primary objectives were feasibility, safety and tolerability, so we’re very pleased to see that the parent and child are doing well,” said the study’s corresponding author Richard Finkel, MD, St. Jude Center for Experimental Neurotherapeutics director and Department of Pediatric Medicine member. “The results suggest it would be worthwhile to continue investigating the use of prenatal intervention for SMA.”

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.

N-of-1: A case study of prenatal risdiplam 

Survival motor neuron protein is most needed in the third trimester of fetal development and the first three months of life after birth. Symptom severity is, therefore, closely linked with the intervention time point. Due to this clinical need, the St. Jude researchers, as part of the Pediatric Translational Neuroscience Initiative, launched a unique clinical protocol to study risdiplam in a single patient. The goal was to determine the feasibility of starting treatment for a fetus with SMA-1 in utero.

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.