Nine-year-old twin sisters dance with bone marrow donor who changed their lives: 'Thank you'

(INSIDE EDITION) - Twin 9-year-old sisters, in dress-up gowns of flowing yellow, recently danced with a stranger who had previously saved their lives.

"It was a very wonderful moment," their mother, Michele Girtler, told InsideEdition.com Thursday. "I was crying. What a selfless act to save two lives an ocean away."

Ingo Gruda of Munster, Germany, did not know little Elizabeth and Kathryn when he agreed to be an anonymous bone marrow donor four years ago. He just wanted to help.

The girls were born with congenital amegakaryocytic thrombocytopenia (CAMT), a condition that left them without platelets, meaning their blood would not clot and the slightest scrape or cut meant they could bleed to death.

Their only hope, doctors said, was altering their DNA via a bone marrow transplant.

But no one in their family was a match. The Mayo Clinic in Rochester, Minnesota, put their names on an international donor-matching service called Be the Match.

Three months later, they got word a donor had been found.

Elizabeth went first, getting her transplant at age 3 in 2011. Kathryn followed a year later at age 4. Doctors did not want to do both procedures simultaneously because the risk was too great that something could go wrong if identical twins with the same last name were in the hospital at the same time.

Their lives have been forever changed.

Before, they were not allowed to play outside. They could not use scissors or any other sharp objects. Their playground was the family's living room.

"They were very sheltered," their mom says. "They weren't allowed in the kitchen if I was in there doing something. They didn't know any different. They never saw other children," except for their older brother, LeeRoy.

But after the transplants, they were able to venture out. They eventually went to school. They still must be careful because their condition also lowers their immune systems, but so far, nothing horrible has happened.

In fact, some rather amazing things have happened. Like meeting Gruda.

Be the Match reached out to Gruda and the Girtlers to see if both parties would like to meet.

Both said yes.

And so Gruda was flown to Minnesota to attend a fundraiser last week for the group, where he met the twins, who were overjoyed, and a little teary, at meeting this man who had done so much for them.

"They were just touched. Once they got onstage, it was like they knew him," the mother said. "They thanked him for saving their lives."

When the dancing started, they stepped out on the floor with Gruda, who held their hands and moved in a circle.

He spoke only German. They spoke only English. But the three danced all night, said Girtler.