Zebrafish help doctors save 10-year-old boy’s life

PHILADELPHIA – Lymphatic systems help clear the body of extra fluids and infection, but when they don't work properly, deadly excess fluid is retained in the body.

That was the case with a young boy whose family sought help at Children's Hospital of Philadelphia.

By testing various medications using tiny fish, doctors miraculously saved his life.

Daniel was a healthy active 10-year-old boy, when his body began to swell. A massive overgrowth of his lymphatic system was overwhelming his major organs.

"He had such an overgrowth of the lymphatic vessels that he was leaking fluid into the pericardium, which is the membrane around the heart," said Dr. Hakon Hakonarson, director of Center for Applied Genomics at Children's Hospital of Philadelphia.

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Daniel’s lungs suffered too, severely diminishing his oxygen. His lung capacity was 23 percent. You know, barely compatible with life,” Hakonarson said.

Doctors discovered the genetic culprit with a blood test and a simple DNA cheek swab. The gene was out of control, meaning Daniel’s lymph system was always in the “on” position, very similar to cancer cells growing out of control. So, doctors began to test anti-cancer medications on tiny, translucent zebrafish.

“The fish develop from a cell to a normal animal in five days,” said Christoph Seiler, research core director, at Children’s Hospital of Philadelphia.

“We put this cancer med into the fish, you can’t give them a pill or an injection, so you basically just put it into the water,” Hakonarson said.

One melanoma drug called trametinib stopped the mutation in its tracks. Doctors then gave the drug to Daniel.

"His lymphatic system essentially normalized. The child came off oxygen, started walking, started running, started biking and he is essentially with normal daily activities," Hakonarson said.

Scientists have long used lab rodents or other mammals to help understand human diseases, but 70 percent of human genes are also found in the zebrafish, making them a good animal for study.