In a world first, a fetus has been treated with a very rare genetic disorder that took her siblings' lives.

The child, now a toddler, was mentioned in a case study published in the New England Journal of Medicine. The ground-breaking treatment was for a lysosomal storage disorder called Pompe disease.

The physicians successfully treated the child, Ayla, using a protocol developed at the University of California, San Francisco (UCSF).

"This treatment expands the repertoire of fetal therapies in a new direction," co-senior and corresponding author Tippi MacKenzie, a pediatric surgeon at UCSF Benioff Children's Hospitals, said, reported SciTechDaily. "As new treatments become available for children with genetic conditions, we are developing protocols to apply them before birth."

Infantile-onset Pompe disease can cause severe damage to major organs of the body such as the heart before birth. Physicians at UC San Francisco started enzyme replacement therapy during fetal development to improve health outcomes for the baby. If left untreated, the disease can turn fatal in early childhood, or lead to low muscle tone, or ventilator dependency.

Ayla received six prenatal enzyme replacement treatments at The Ottawa Hospital before being born at term. Currently, at 16 months of age, the child is undergoing postnatal enzyme therapy at CHEO (a pediatric hospital and research center in Ottawa, Canada) and is doing well.

"When we were having Ayla, we didn't know if she'd be able to walk," Zahid Bashir, Ayla's dad, said, as per the outlet. "We didn't know if she'd be able to talk. We didn't know if she'd be able to eat. We didn't know if she'd be able to laugh. So, as she hits each of these milestones, we continue to be amazed at her progress. So, yeah, it's quite something, that I think sometimes we may take for granted, but most of the time we're quite aware that she's a miracle."

Typically, children born with Pompe disease have enlarged hearts and die within two years without treatment. Extremely rare, the disease occurs in less than 1 in 100,000 live births. It is caused due to genetic mutations that affect the production of an enzyme called acid alpha-glucosidase that breaks down glycogen. The mutation leads to the accumulation of dangerous levels of glycogen in the body.

"We have been treating our fetal patients using intrauterine therapy for more than 30 years," Karen Fung-Kee-Fung, the family's maternal-fetal medicine specialist at the Ottawa Hospital, said. "The emergence of a new medical treatment to lift the burden of Pompe disease for this family, and potentially help other families affected by devastating genetic diseases, is both exciting and incredibly satisfying. We feel very privileged and honored to be a part of this international collaboration to help make this first-in-the-world treatment a reality."