Published: Jan 06, 2012 8:50 PM EST

KANSAS CITY, Mo. (AP) - Eight-week-old Carver Bayless is a lucky guy. So is his 4-year-old brother, Granton.
    
The Bolivar, Mo., boys were both born with a rare genetic condition that robbed them of a functioning immune system. "Bubble boy" is the common term for children like them, kids who must be sheltered from every stray germ because even the most common infections that children usually brush off can turn into a deadly illness.
    
On Dec. 16, Carver received an infusion of umbilical cord blood from an anonymous donor. Doctors at Children's Mercy Hospital hope the blood's stem cells will take root in his bone marrow and create a new working immune system for him.
    
Granton, who spent his infancy perilously close to death, underwent the same transplant procedure at Children's Mercy in 2008. He's healthy and active now.
    
So far, Carver is doing well, too. He's in an isolation room at Children's Mercy where his parents, Jenni and Daniel - dressed in surgical gowns and masks - tend to him around the clock. Daniel, 34, is an English teacher and coach at Bolivar High School. Jenni, 30, is an elementary school art teacher who has set aside her career to care for her children.
    
"In my mind, I wasn't thinking this would happen again," Jenni said. "It was not a planned deal, but it was a good deal."
    
Jenni already was pregnant with Kaylynn, the Baylesses' middle child, before Granton was well enough to leave the hospital. Girls aren't affected by Granton's condition, so there was no reason for concern.
    
But when Jenni discovered she was pregnant again with another boy, she and Daniel knew there was a 50-50 chance their third child would have the same problem as Granton.
    
"The moment we tested Carver's blood and found his (immune cell) level was low, we told them to come here," said Jignesh Dalal, chief of the bone marrow transplantation section at Children's Mercy.
    
Carver and Granton were born with a condition called severe combined immunodeficiency, which occurs once in every 50,000 to 100,000 births, Dalal said.
    
Because it's so rare, newborns generally aren't tested for the condition. Babies can become severely ill before it's recognized.
    
In Carver's case, his doctors and parents knew what to expect, and a transplant was arranged quickly. But for his older brother, Granton, the going was rough; he became seriously ill and battled life-and-death infections while he was at Children's Mercy.
    
"It looked like he was going to die every day for three months," Daniel Bayless said.
    
"He was in such critical condition," Dalal said. "Very few successful transplants are done when a child's condition is so bad."
    
Dalal said the hospital's staff asked Granton's parents to consider whether they should let their son go. "We are not doing something for him, but to him."
    
Daniel said he and Jenni struggled with their decision.
    
"As his parent, it was our job to act in his best interest," he said.
    
Jenni and Daniel spent the weekend praying and decided to go ahead with the transplant.
    
"While there was still a sliver of hope, we had no other choice," Daniel said.
    
Transplants of either bone marrow or umbilical cord blood from healthy donors can restore bubble babies' immune systems. Both contain a type of stem cell that can regenerate healthy blood and immune cells.
    
A suitable bone marrow donor for Granton proved hard to find, so umbilical cord blood from a cord-blood bank was used.
    
"When we decided to move forward, there was not much time left," Dalal said. "The question was how fast we could do it."
    
Dalal breaks out into a big smile and a hearty laugh when he thinks about how well Granton is doing now.
    
Granton's parents also are amazed.
    
"He's doing better than my greatest dreams," Daniel said. "At one point we thought if he lived he would be on a ventilator all his life. Now, he's climbing around like a monkey, terrorizing his sister, doing things boys do."
    
Granton and Kaylynn have been staying at their grandparents' farm in Kansas while their parents stay with Carver. They're eager to see their new brother.
    
But that will have to wait, their parents tell them. It will be months before Carver will be able to leave the hospital, about a year before his new immune system is as robust as that of a healthy newborn.
    
"We're trying to give them ways that they'll understand," their father said. "We say, 'You can see Carver when the trees turn green.' "
    
___
    
Information from: The Kansas City Star, http://www.kcstar.com

(Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)