he died of a rare, unknown disease — that in a matter of hours caused his brain to swell and organs to shut down.

Now, Natalie and Don Wallace of Norristown are desperately searching to find out what killed their little boy. Doctors from top hospitals — the Mayo Clinic, Johns Hopkins, The Children's Hospital of Philadelphia — were unable to identify the disease. After exhausting medical options available to them, the Wallaces are appealing to the public for help.

They can't give up.

Ben has it, too.

On the two-year anniversary of Zach's death last month, Natalie sat behind her computer monitor, praying and crying.

She poured every bit of emotion and frustration into a detailed e-mail about her family's struggle and fired it off to every person she knows, asking each of them to do the same. Maybe her story would reach a doctor familiar with this illness, a talk show host who could reach a mass audience, a mother battling the same disease thousands of miles away. All she knew, she said, is that her family could no longer shoulder the fight alone.

“We were at a dead end,” said Natalie, as she scurried around the house picking up toys so Ben wouldn't bump into them. “I live every day petrified that Ben will get sick and we won't be able to save him. I don't want to let him down. I feel in some way I've let Zach down. ... It's a mother's guilt, I know, but it never goes away. ... The unknown is always there; we just want answers.”

A call the next day was proof of just how far and fast her message had traveled. A Minnesota mother, Tricia Gingras, who launched a public campaign to understand a disease that made her daughter incapable of feeling pain, got the attention of Oprah and several other talk hosts, who aired her story to a national audience. About eight families then came forward with children who faced the same diagnosis. This mom promised to help Natalie get out the word. Gingras, too, knew the pain of the unknown.

“That gave me such an inspiration,” Natalie said. “I felt there's a chance that our story cannot just get us help but get others help as well. What if there's a family thousands of miles away battling the same disease?”

The disease was first discovered when Zach was only 2 years old. He spiked a high fever and appeared lethargic. Don and Natalie, then 9 months pregnant with Olivia, rushed to the hospital, where Zach started convulsing.

“His platelet counts were dangerously low, his blood pressure was skyrocketing; he was going into renal failure; his liver and spleen were enlarged. Then he went into a coma. ... We practically lived there for three months.”

In that time, Natalie gave birth to baby Olivia, which was the only night she spent away from Zach's bedside.

“Here I had a brand-new baby I was trying to nurse, and Zach was in this state, and basically, they had no answers; I thought that was hell — but hell was losing Zach.”

When the Wallaces brought Zach home, he couldn't walk or see, but in the following months, his sight would return, and over the following two years he would learn to get around using a walker.

“Whatever it was, we thought, it wouldn't happen again. Look how healthy he looked; he was so happy and full of life,” said Natalie, leafing through a scrapbook of Zach's photos: Zach at the beach building a sand castle with his dad; Zach with his arm around his sister, Olivia, on the beige-carpeted steps of their home; Zach dancing with his walker at a wedding and a picture of Zach on his fourth birthday behind a candle-lit cake, taken just days before a larger celebration, his Bob the Builder-themed party, was planned.

The next few pages of the scrapbook are empty.

Two days after that picture was taken, he got a virus, and he was rushed to the hospital, where Natalie and Don learned he suffered multiple strokes that left his brain swollen. His organs shut down. Early the next morning, he was gone.

“It happened so fast, and when we got home, the decorations were still up and the house was sickening quiet,” she said. “I was two months pregnant with Ben and didn't think I'd be able to carry the pregnancy.”

She missed the sound of Zach clamoring around the house in his walker, playing hide-and-seek and singing the theme of “Jay, Jay the Jet Plane.” And Olivia, just 2, kept asking, “Where Zach?”

“She asked for Zach for almost a year after he died. We told her Zach got sick and that it was his time to go with God. It was hard on her too; there wasn't anything they did do apart.”

Olivia, now 4, has shown no signs of illness.

When Ben was born, life seemed different, “like we were given another chance, a new start,” Natalie said.

Then at 5 months, Ben got a fever. His symptoms were eerily familiar. She rushed him to the emergency room, and when Ben awoke from his nap, he looked right past her. She knew he was blind.

“The symptoms were identical to Zach's, the seizures, the blindness; we almost lost him too,” she said. She pleaded with doctors to do a platelet count and other tests. She knew his body was destroying his blood cells and his organs were shutting down.

Dr. Edward Attiyeh, an oncologist with CHOP, said knowing that the disease was genetic made it easier to treat Ben. “This is a one-in-a-million kind of rare disease,” said Attiyeh, who also treated Zach.

He said the illness resembles a very rare blood disease, where the body destroys blood cells, triggers clots in blood vessels and then leads to organ failure and brain injury. “We do know that certain proteins in the blood, when abnormal, can trigger this kind of event. We didn't know that with Zach. We had no way of knowing whether it was something inherited or something he acquired.”

Doctors, he said, are hoping for a medical breakthrough in the study and identification of proteins so they can target the protein in Ben that is causing the episodes. “Right now, it's like finding a needle in a haystack,” he said.

In the meantime, Ben is treated with steroids, antibiotics and blood pressure medication. His sight is slowing returning; he can recognize faces a few inches away. He is at CHOP weekly for plasma replacements, something Zack did not undergo regularly.

But his weekly hospital visits, where he is pricked with sometimes five needles before nurses find a vein, are Ben's only trips outside of the house.

“We don't even let Olivia go to school because we're afraid she could get sick and Ben could get sick ... and then we wouldn't be able to save him,” said Natalie. “He's not exposed to any sickness, but I know that's no way to live.”

Don said faith in God keeps them going. “I never imagined the road we traveled would go this way. We're regular people going through life as best as we can. People say we're doing well, but it doesn't feel like we're doing so well sometimes. We take it one day at a time; it's the only way we can handle it.

“... And we know we'll see our son again one day. He will live forever.”

Olivia still misses her brother. Zach would have been 6 last month. Together, the family released balloons into the sky “to send them to Zach in heaven.

“... Olivia asked me if Ben's going with God too. "Not now,' I tell her, but she's still worried. We all are. We'd go to the ends of the Earth to save him,” Natalie said.

Marion Callahan can be reached at 215-345-3166 or mcallahan@phillyBurbs.com.