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Ear infections, runny noses, colds and hernias are all common ailments among young children. But for Jason and Justin Leider of Elmwood Park, N.J., these were signs of something much more serious.

Four-year-old Jason had just started preschool when his parents got a phone call that would set in motion the discovery of a devastating diagnosis, and the family’s desperate journey for a cure.

“The teachers called us after about six weeks of school and said that something just doesn’t seem right,” Jason’s mother, Deena Leider told FoxNews.com.

Jason’s teachers were concerned that he was showing developmental delays, and urged his parents to get him evaluated to see if he fell somewhere on the autism spectrum. So Deena Leider and her husband Jeff decided to take Jason to see a neurologist.

“We went to Dr. Judy Wu in Fairlawn, N.J., and she said ‘autistic, not,’ she said ‘ADHD, possibly, yes, he's very, very excitable, he's very playful,’ she said, ‘But did you ever notice that he doesn’t really look like you,’” Deena recalled. “And then she started looking at his hands, and she asked medical questions—ear infections, runny nose, hernia—he had it all. She said, ‘This looks like a genetic disorder’ and she wrote down on the piece of paper, mucopolysaccharidoses.”

Mucopolysaccharidoses refers to a group of rare metabolic disorders caused by the deficiency of certain enzymes needed to break down and recycle complex sugar molecules found in the cells of the body.

Wu had a hunch, but she didn’t want to diagnose Jason herself, so she referred the Leiders to Dr. Helio Pedro, chief geneticist at Hackensack University Medical Center in New Jersey.

“We went to see the geneticist and he said, yes, mucopolysaccharidosis,” said Deena. “And we sat there and listened to the symptoms and everything and we're looking at each other, and we knew Justin had it too.”

Pedro diagnosed Jason and his 2-year-old brother Justin with MPS II in February 2011.

“There are different types of mucopolysaccharidosis, or MPS, and MPS II is one of them where there is an accumulation of these sugars called glycosaminoglycans,” said Pedro. “It accumulates all over the body, all different organ systems -- the respiratory system, cardiovascular, gastrointestinal system, liver, spleen, and in some cases, the brain as well.”

As a progressive disease, or one that gets worse over time as the waste builds up in different organ systems throughout the body, children with MPS II usually don’t survive beyond their teens, according to the MPS Society. Many patients often experience a gradual loss in skill and may even lose their ability to walk, hear and communicate with those around them.

“Just to hear as a parent, that your little boy, you know, was basically given a death sentence, was difficult for Deena and I,” Jeff Leider said. “All my dreams and goals and fantasies and things that I’ve thought of as a father, all went out the window, it was gone, it was over, my slate was wiped clean. I have two little boys, and they’re gonna go.”

Although MPS II has been shown to occur in females, the condition most often affects males, who inherit an abnormal copy of the iduronate-2-sulfatase (I2S) gene from their mother.

“Women are a carrier for the condition, and when they have a child, if that child happens to be a boy, there's a 50 percent chance of [him] having that condition,” said Pedro. “It’s a strictly genetic condition and is strictly based upon the mutation within that specific gene on the X chromosome.”

At the time of Jason and Justin’s diagnosis, Deena was eight months pregnant. She and Jeff had decided not to find out the sex of the baby before delivery, but now they had to face the grim reality having a boy would mean a 50 percent chance of another child with MPS II.

“Luckily, when Deena gave birth, Jordan Kenna came out and it was a girl,” said Jeff. “She’s our little miracle, but if you look at it on the flipside, is Jordan gonna be old enough to know her brothers—but if she knows her brothers—she’s got to bury her brothers.”

While a simple urine or blood test can confirm a diagnosis of MPS II, it often goes undiagnosed or remains misdiagnosed for years.

“Most children don’t get diagnosed until about four, so they’ve literally had a poison building up in their body,” Deena said. “And the reason they get misdiagnosed is that the symptoms are normal, common, everyday, pediatric childhood symptoms: runny noses, constant ear infections, hernias, and congestion.”

Jason and Justin have not started showing outward signs of the disorder’s progression thanks to the enzyme replacement therapy they receive each week at Hackensack University Medical Center.

“I think that with the enzyme replacement therapy, I actually think that they are getting a little bit better from a respiratory component,” said Pedro. “And I just hope that things keep on improving and we'll see a lot of benefits in regards to that.”

But as grateful as the Leiders are for the life-saving infusions keeping their boys alive, it all comes at a hefty price—and for the boys, it’s costing them a good part of their childhood.

“It’s not easy for the boys, you know. They have physical therapy, speech therapy, occupational therapy, four to five hours, once a week and they go to countless doctor appointments and check-ups,” explained Deena. “So they’re not normal kids, they don’t get to be little boys.”

Yet despite the everyday struggle, Deena and Jeff have found support in their local community with individuals offering not only financial assistance but also providing Jason and Justin opportunities that they might not have received otherwise.

“Elmwood Park Police Department chose Jason and Justin to be Police Chief and Police Deputy for the day,” said Deena. “They got picked up in a police brigade, had little mini uniforms, and they went to the police station and got sworn in. It was just a great day”.

In an effort to increase awareness about Hunter syndrome, Deena and Jeff established their own organization for fundraising and research called “Let Them Be Little.”

“What I’m trying to do is make awareness for children because [Hunter syndrome] is a misdiagnosed disease and it’s very rare,” said Jeff. “Let’s face it, parents would do anything for their children and this is the only way we know that we can do something for them.”

Despite the challenges of managing two young children with Hunter syndrome, both Deena and Jeff remain hopeful and refuse to let the condition dominate their lives.

“The way I look at it is, enjoy each and everyday with your kids, regardless if they’re healthy or sick and like Deena says, enjoy that smile, enjoy that time that he wants to sleep in your bed with you,” said Jeff. “Our journey will continue, and our journey continues and we'll see where we go with Jason and Justin.”

Click here to read more about the Let Them Be Little Trust Fund.