“These children shouldn’t have to live out life in a wheelchair when they could run, walk, and play,” says Davis, a founder of the Texas SMA Newborn Screening Coalition.

Time is of the essence in treating SMA type 1. A single mutation in the SMN1 gene causes swift and irreversible damage to a baby’s motor neurons, which are located in the brain stem and spinal cord. This damage leads to muscle weakness, and children eventually develop trouble swallowing and breathing.

Davis’s son, Hunter, who is now six years old, had already lost all movement at two weeks of age. Hunter is alive thanks to Spinraza, a breakthrough SMA drug approved in December 2016. Children who have received the drug have made remarkable recoveries. But it must be given through a spinal tap once every four months, for life. It costs a whopping $750,000 for the first year of treatment and $375,000 every year after that.

AveXis’s gene therapy is meant to be a one-time treatment, infused into a vein during a 60-minute procedure. It uses an engineered virus to deliver healthy copies of the SMN1 gene to cells throughout the body. Once there, the new gene starts making a protein that’s essential for the survival of motor neurons.

If you wait, however, “the children have limited motor neurons for the gene therapy to get into and work effectively,” says Sukumar Nagendran, AveXis’s chief medical officer.

On average, the 15 children in the AveXis trial received the gene therapy four months after birth. They all responded, but Nagendran says two children who got it within the first two months of life had the most dramatic improvement; they’re now able to walk independently.

In April, AveXis began a new study, this time treating babies immediately after birth. The results will be able to tell researchers just how much better patients fare when they get the drug as newborns.

Other gene therapies may also work better in children before a genetic defect has time to irreparably damage the body. For example, Bluebird Bio is developing one that halted a deadly brain disorder called cerebral adrenoleukodystrophy (ALD), also known as Lorenzo’s Oil disease, in 15 out of 17 children. In a statement provided to MIT Technology Review, the company said outcomes are better when patients are treated before symptoms appear.

State by state

On February 8, a national committee that oversees newborn testing voted to recommend that SMA be added to the recommended universal screening panel. The next step is for the secretary of the US Department of Health and Human Services, Alex Azar, to sign off.

Even then, rolling out SMA screening for every newborn isn’t a done deal. A recommendation put forth by the committee is just that—a recommendation. It’s only binding in two states, California and Florida. Other states may choose to adopt the proposal or not.