Chris Trebing was a 'savior sibling' as a baby for his sister, Katie. Now he's getting ready for college.

Sitting down to craft his college application essay earlier this year, Christopher Trebing, a senior lacrosse player at Smithtown East, decided to write about his unique role as the youngest member in his family of five: a so-called savior sibling.

It wasn't a role he chose, he wrote. In fact, he had no say in it at all. But, he wrote, it nevertheless was a role for which he was born.

One, he said last month, that has come to define him as well as inspire him.

His parents, Steve and Stacy Trebing, used in vitro fertilization, combined with a test called preimplantation genetic diagnosis, to conceive Chris and ensure he would inherit a specific portion of DNA that matched that of his sister, Katie. She was born with Diamond-Blackfan Anemia, or DBA, a rare disease that kept her bone marrow from producing enough of the red blood cells needed to carry oxygen throughout her body.

When the Trebing's eldest child, Cal, proved not to be a genetic match to Katie, Steve and Stacy, after countless consultations with medical professionals — and after months of soul-searching, research and anguish — decided to pursue the procedure that would not only lead to the birth of Chris, their third child, but ensure the chance he might donate the marrow that could save their daughter's life.

As chronicled in a five-part series in 2007 by Newsday reporter Beth Whitehouse, who later wrote a book about the Trebings titled "The Match," the lifesaving procedure worked.

Katie, 19, is now a sophomore nursing student at the University of Miami.

And Chris, 17, has been accepted to Babson College in the Boston suburb of Wellesley, Massachusetts, where he plans to play lacrosse next September.

Chris organized a Thanksgiving weekend charitable 5K run and walk at Heckscher State Park to benefit the DBA Foundation. The run raised $6,100 for the foundation, Steve Trebing said Thursday. 

"My parents chose me from a petri dish for my DNA," Chris wrote in his college essay. "While this sounds harsh, it has defined the person I have become and the person I wish to be … I hope to be the hero for families who were not as fortunate as mine and did not have the ability to have a savior sibling."

Trebing said he got the idea for the charity event while on a run of his own earlier this year. His father was putting the finishing touches on a book that debuted earlier this month. Titled "Saving Katie," it is a memoir about the family ordeal that began when the Trebings first learned Katie, then an infant, had DBA — and the search to find a cure for the blood disorder that causes a litany of debilitating, even fatal, medical conditions.

Chris was barely 1 year old when he donated the bone marrow.

But, he said recently, throughout the years that followed, he constantly had people telling him he was "a hero" — even though he had no idea or any say in what he'd done.

"I was just a little kid, trying to play with my Legos," Chris said. "I didn't know any better. But it was the atmosphere I was put in at a young age and I felt there was pressure I was under to be the hero, these people all coming up to me, saying 'congratulations,' and I didn't even know what I'd done yet."

Chris said over the years, as he learned more of the back story, he'd gained perspective on his role in helping save his sister. He said he'd found inspiration in that.

"I've become more mindful of what my family's been through and I definitely look back on the story and I'm inspired," he said. "I feel like it's made me feel like I need to do more, to give back, to be better. I think it's made me place a burden on myself, to be the best I can be."

While Katie Trebing still has constant reminders of what she went through — there will be lifelong medical follow-ups, including continuing blood tests to monitor her health — she said the years since the lifesaving transplant had inspired her, too. It's one reason she's pursuing a career in nursing.

"I feel like I have more gratitude toward things I don't think I'd appreciate as much if I hadn't gone through what I've gone through," she said. "That connection with my family. That fact that I realize they — and, the doctors and nurses who I dealt with — gave me as normal a childhood as they could."

The Trebing children — Cal just finished at Vassar College and recently was accepted to the University at Buffalo School of Dental Medicine — also are learning more about what their parents went through.

In his book, Steve Trebing recounts how, after months of agonizing research, he and Stacy decided to have Chris to pursue the transplant procedure to save their daughter, a procedure then with a 90% success rate. Then they attended a camp in Maine for children and their families dealing with cancer and other life-threatening diseases.

"We'd just made our decision and then we were given a letter written by a family whose child had just died as a result of the transplant, one in the 10% that failed," Steve Trebing said. "And it was just heart-wrenching. It made us wonder if we'd considered all the implications. It made us think."

Both Steve and Chris acknowledged neither had ever considered what might have happened if the procedure had failed — what burden that might have placed on Chris if Katie hadn't survived.

"You kind of take for granted that the stars aligned and it worked out," Chris said. "To think what might've happened if it hadn't, that's a whole other world."

In his book, Steve Trebing recounts an emotional confrontation with the father of a bride who had hired his tent rental company for a beach wedding in West Hampton Dunes, and how he was forced at the last minute to scrap the beachfront scenario due to tidal surge from a looming Atlantic tropical storm. Forced to move the tent to a nearby parking lot, Trebing was confronted by the angry dad just as he received a call from Stacy, at Sloan Kettering, with news that the bone marrow transplant from Chris to Katie had begun to work.

"All I could think was, 'Oh, my God.' If he only knew what's really important in life. That, so what if wasn't going to be the fairy-tale wedding they'd dreamed of."

Now, Trebing said, he also understands the father was just trying to protect the most important day in the life of his daughter — while Steve was dealing with the very life of his daughter.

He said that moment, as well as dealing with hate mail from those opposed to what he and his wife had done, added to "an emotional roller coaster" that had lasted years for Steve and Stacy.

"There's always one or two people who want to confront you, who don't understand or don't agree, and what I've learned is this," Trebing said. "If you had a child who was sick and you were in our shoes, you'd have a different understanding of what we've done. You'd do the same thing."

As he said: "We're just grateful over who our children have become. We're very thankful."

By John Valenti

john.valenti@newsday.com

John Valenti, a reporter at Newsday since 1981, has been honored nationally by the Associated Press and Society of the Silurians for investigative, enterprise and breaking news reporting, as well as column writing, and is the author of “Swee'pea,” a book about former New York playground basketball star Lloyd Daniels. Valenti is featured in the Emmy Award-winning ESPN 30-for-30 film “Big Shot.”