After 16 years fighting a rare, life-threatening disease, Derek Gropp finally met the organ donor who would save his life — his 3-year-old brother, Christopher.

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Derek was born with Kostmann syndrome (commonly known as severe congenital neutropenia), which prevents the body from producing white blood cells critical to fighting infections and makes even a common cold or an ear infection potentially fatal.

Because the disease can transform into leukemia, Derek's family knew their son might one day need a bone marrow transplant.

Then along came Christopher, who in 2016 proved to be nearly a perfect match for his big brother.

But the case presented unique challenges. At just 40 pounds, then-preschooler Christopher was nearly one-third the size of his 150-pound brother. Their age gap also was a factor.

"We have had donors as young as Christopher, but the recipient is usually another child close in age or size," says Sung Won Choi, M.D., a pediatric hematologist-oncologist at the University of Michigan C.S. Mott Children's Hospital, where Derek receives his care.

"What's incredible about this story is that bone marrow was donated from a 3-year-old to a 16-year-old," Choi says, noting the difficulties of the exchange. "In order to give Derek a bone marrow transplant, we essentially had to take out Christopher's entire blood volume."

Challenges and success

Since Derek's diagnosis at age 1, the family made the 900-mile, five-state trek from their home in Salina, Kansas, for care with the immuno-hematology team at Mott. In 2014, the family temporarily moved to Ann Arbor for regular appointments in preparation for the transplant.

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"Because of the size difference between them, not many centers may have done the transplant," says the boys' mother, Lisa Gropp. "Other places would likely have told us to wait for another match from a donor we didn't know to avoid the risks.

"The fact that the Mott team was willing to do this transplant speaks volumes for what brilliance Derek's doctors brought to the table, along with confidence and knowledge to be able to make these life-changing decisions for my children."

Last year, the Mott team used a bone marrow growth factor to stimulate white blood cell production in Christopher. Doctors had planned to freeze the bone marrow cells, expecting to need possibly two rounds to collect the amount of cells Derek needed.

But Christopher, now 4 years old, proved to be a "fountain of marrow," according to doctors, providing more than enough marrow on the first try.

Derek then underwent a nearly five-hour-long infusion to replace his bone marrow with healthy cells from his baby brother.

A lifesaving connection

When Derek was diagnosed as a baby, Lisa Gropp was told her child might not live past age 4. He was in and out of the hospital and on medications since.

Today, thanks to his brother's gift, his body shows no signs of ever having Kostmann syndrome.

"A bone marrow transplant was Derek's only chance of a cure. Without it, he would die," Gropp says. "He's too young to understand it now, but Christopher will grow up knowing he was our greatest gift. He saved his brother's life.

"He turned out to be our little hero."

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A year later and now 17, Derek continues to do well. He's able to travel more easily than ever and spend quality time with family members like his grandmother.

His mother also hopes the siblings' shared bond encourages more people to understand the importance of bone marrow donation.

"We are very grateful for his new life and ability to do these things. These are all big milestones," Gropp says. "Every day I pray their story, especially Derek's survival and the transplant, will inspire and give others hope when they feel scared and in despair."

"We would never wish for any child to ever endure all he has, let alone another parent watch their child suffer. Derek has overcome so much in life. If it eases the heart of one parent or inspires one person to become an organ donor, that would mean so much to me."

Photos courtesy Katie Ventura Photography