A Long Island father gave part of his liver to his baby son after a rare genetic disorder left the child fighting for his life, and he says he would “do it again in a heartbeat.”

Brian Carstens told PEOPLE that his son Benjamin started showing signs of trouble within days of his birth in the fall of 2024. Benjamin was not eating enough, and abnormal newborn screening results led doctors to find dangerously high ammonia levels.

Benjamin was rushed to the pediatric intensive care unit, where medications did not lower his ammonia levels fast enough. Doctors then placed him on dialysis.

“Benjamin was so small,” Brian, 28, said. “We were in shock and completely devastated.”

Genetic testing later confirmed ornithine transcarbamylase deficiency, a rare metabolic disorder that can cause life-threatening spikes in ammonia. Brian said dialysis stabilized Benjamin, and an MRI showed he had not suffered brain damage, but he and Benjamin’s mother, Karla Hernandez Garcia, were told another crisis could happen at any moment.

“In our minds, Benjamin felt like a ticking time bomb,” Brian said. “We became obsessed with learning everything we could about OTC deficiency.”

Doctors told the family that medications, supplements and a specialized diet could help manage the condition, but that a liver transplant was the only cure. They were referred to Hassenfeld Children’s Hospital at NYU Langone, where they learned Benjamin needed to grow large enough to safely undergo surgery.

Brian said he asked if becoming a living donor would improve his son’s chances, and the answer settled it for him.

“To me, it was not something I had to think about,” he told PEOPLE. “Living donor liver transplants are associated with higher patient and graft survival. The data on that is clear. As Benjamin’s father, I knew I had to donate and give him the best chance I could.”

The transplant was scheduled for Aug. 18, 2025, Brian’s birthday.

“At that time, all I cared about was making sure Benjamin had the best chance at a healthy life,” he said. “But when we were told the date of the surgery, we were shocked by the coincidence.”

Brian said he and Karla stayed with Benjamin at Hassenfeld Children’s Hospital the night before the operation. He said saying goodbye before being taken to his own operating room was one of the hardest moments.

“I wanted to stop and get up so I could give them one more hug and kiss,” he said. “But I wasn’t strong enough to do it. I would have broken.”

“Karla was strong through it all, keeping Benjamin happy and making sure he felt loved,” he added.

Before anesthesia, Brian said he had one final request for Benjamin’s surgeon.

“I asked him to please take good care of my son,” he recalled. “He assured me he would.”

When Brian woke in the intensive care unit after surgery, he said his first question was about Benjamin, despite being in “a lot of pain.”

“As soon as I woke up, I asked how my son was doing,” he said.

Benjamin was still in surgery at the time. Brian later learned his son had made it through the transplant, and he urged Karla, a registered nurse, to stay with Benjamin.

The next day, Brian was wheeled to Benjamin’s room. He said he could not lower the crib rail himself because of pain from surgery, so the surgeon helped him reach his son.

“The moment I reached for Benjamin’s hand and touched it, I started to cry,” he said. “It was an incredibly emotional moment.”

Now, nine months after the transplant, Brian said both he and Benjamin are doing well.

“He is happy and healthy,” Brian told PEOPLE. “Watching him play, smile, and laugh brings me immense joy. It still feels surreal.”

Brian said he has fully recovered from donating part of his liver.

“I would do it again in a heartbeat just to see Benjamin the way he is now: thriving and full of life,” he said. “We went from crying tears of fear to crying tears of relief and joy.”

Brian said he and Karla, who have been together since high school, hope to get married after putting their plans on hold during Benjamin’s recovery.

“We are high school sweethearts [and] have been together since 2015. Once Benjamin was born and his health complications began, we put everything on hold to focus entirely on him,” Brian explained.

He also said the family remains grateful to the transplant team at Hassenfeld Children’s Hospital at NYU Langone.

“Sharing our story feels deeply personal,” he added. “But if it can help even one person better understand living organ donation, or inspire someone to consider it, then it is worth it.”

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