6-Year-Old Quarantined for 726 days with Deadly Disease Gets 'Miracle' Treatment

Two Columbia, South Carolina, parents are in a race against time to save their 6-year-old daughter from a rare and deadly disease.

At just 3 years old, Eliza O'Neill was diagnosed with Sanfilippo syndrome – a genetic, debilitating disorder that prevents the body from properly breaking down sugar, resulting in nerve damage, brain damage, blindness and eventual death.

In July 2013, Eliza's parents learned about a clinical trial that could help their daughter.

"It was her only shot," her father Glenn O'Neill tells PEOPLE. "We did everything in our power to make it happen."

Endless Determination

The couple, who started the Cure Sanfilippo foundation, raised the $2.5 million needed to get the drug production started in December and patiently waited to find out if Eliza would be selected.

"It was agonizing," Glenn says, "but when we got the phone call she was chosen, we couldn't believe it."

Eliza is the first child in the world with Sanfilippo syndrome to receive the treatment, and since she began the clinical trial in May, Glenn says that he and his wife Cara now have hope for their daughter's future.

"To go from knowing for certain that your child is fading away with every second and knowing that she is getting worse and worse to a feeling of maybe this is stopping it," he says, "is indescribable."

He adds, "Maybe she is actually getting better. We're witnessing a miracle."

For the O'Neills, a miracle doesn't mean Eliza will go back to being a typical 6-year-old girl. For Glenn, he says that it could mean preventing her from regressing and dying in her teenage years.

"The kids who are untreated have feeding tubes because they can't eat, they get wheelchairs because they can't walk, they have terrible seizures and they pass away," he says. "Imagine if none of that stuff happens to my daughter. Imagine if she can relearn the things she’s lost."

While it's too soon to tell if she's improved since the trial, Glenn does see a light in his daughter's eyes that he hasn't seen since she was diagnosed as a toddler.

"It's hard to explain, but there are these moments of clarity where she previously was looking through us and she would run right by," he says. "You would even wonder if she knew who was there or what was going on. Now she will sometimes stop, look and try and make these words that we know she knows."

Glenn and Cara want other parents with a child who has Sanfilippo to get the treatment Eliza received at Nationwide Children's Hospital in Columbus, Ohio.

"Every child with this disease should have this chance," he says. "It's why we created our foundation. They deserve the chance to live and thrive."

Since Eliza received the treatment, a second child has been enrolled and treated, according to a press release from Abeona Therapeutics.

Before Eliza got accepted into the clinical trial, the family made the difficult decision to live in a self-imposed quarantine to prevent Eliza from getting sicker.

The common cold could have accelerated her symptoms and if she developed antibodies to a common virus she would be receiving in the trial, it could eliminate her from the study.

For 726 days, Glenn, Cara, Eliza and her 9-year-old brother Beckham rarely left the house. When they did, they avoided people and spent time at the beach or at an open field.

Beckham, who started fourth grade on Monday, is back with his classmates after being homeschooled for two years.

"The decision we made weighs heavily on us, but we see that Beckham has gotten through it and he understands why we've done this for his sister," says Glenn. "He's back with his friends and nothing makes us happier than to see that."

Now that they're no longer in quarantine, they're taking advantage of the freedom they lost almost two years ago. The family is back to attending birthday parties, the zoo, the gym, the pool and even find going to the grocery store exciting.

"It's amazing," he says. "It was a long time."

But most importantly, Glenn is grateful for one thing – the opportunity to save Eliza.

"She has a chance," he says. "Now we have to wait."