Mia Hamm's brother died following complications from a bone marrow transplant. Now the soccer star is speaking out about a common risk of the procedure.

Soccer star Mia Hamm is not only an advocate for women in sports, but for awareness around bone marrow and cord blood transplants — both of which she works for through the Mia Hamm Foundation, which she founded in 1999. That was just two years after her brother Garrett died of a fungal infection following his own bone marrow transplant.

Now Hamm is partnering with the pharmaceutical company Incyte on a campaign to spread awareness about another potential complication of bone marrow transplants: graft-versus-host disease (GVHD).

Here, Hamm answers questions about her advocacy work and what the average person can do to help the bone marrow transplant community.

How does the Mia Hamm Foundation help people who need a bone marrow transplant?

Hamm's mission with the Mia Hamm Foundation is two-fold: to encourage people to sign up for the bone marrow registry, and to offer financial aid to the families who are navigating the procedure. Now, she's added another point to the foundation's mission: spreading awareness about GVHD.

"We’re urging people who are on their own bone marrow transplant journey to learn about GVHD, and what symptoms to look for," Hamm tells Yahoo. "Any small change, they should reach out to their health care team, because they can prevent long-term consequences."

Though Hamm's brother Garrett passed away from an infection that was a different side effect of bone marrow transplants, it was Garrett's experience in the hospital that led to Hamm learning about the devastating effects of GVHD.

"We didn’t know about GVHD until someone else in the ward had it," she says. "That is another reason for me — rather than being reactive, we need to be proactive, and get the information out there for families so they can make the best decision."

What happened to your brother Garrett?

Garrett was adopted at age 8, when Hamm was 5, she says. It wasn't until he was 18 that he became sick with aplastic anemia.

"He went through drug treatments and went into remission, but came out of remission and had what’s known as myelodysplasia [a type of bone marrow cancer]. That’s when the doctors told him he needed a bone marrow transplant," Hamm says. "He was looking for a donor, and we couldn’t find one. We ended up finding his biological father, who was his donor."

Though Hamm says the transplant was going "really well," his immune system was "shut down" prior to the treatment, leaving him vulnerable.

"He had this fungus in his body that you and I could fight every day with no problem, but when you’re immunosuppressed, it’s very hard," she says. "That’s what ended up taking his life. For me, it’s not necessarily about what took his life, but the challenges of what bone marrow transplant recipients go through, which is why I partnered with Incyte."

What can the average person do to support the bone marrow transplant community?

Hamm stresses the importance of signing up on the national bone marrow registry.

"The more diverse we become as a country and as a globe, the more people we need in the registry. I think it’s important to share the stories of unrelated donors," she says. "A lot of times, you hear, ‘Oh, it was my sister who was my donor’ — but the selfless act of someone registering not even knowing whose life they could save, and taking the time to do that and go through the process, is so admirable and heroic, that those stories need to be shared. You have the opportunity to save someone’s life."

Hamm directs people to Marrow.org, which connects to the national registry.

"You can also reach out to the Red Cross to see if there are bone marrow drives. However, sometimes you’ll hear in your community that, 'Hey, someone in our community has leukemia, and we’re doing a bone marrow drive,'" she adds. "The other thing that’s important to stress, is that when someone calls you, say yes."

What an expert says

What is a bone marrow transplant?

A bone marrow transplant is the process in which a patient has an infusion of healthy stem cells — the immature cells that develop into red blood cells, white blood cells and platelets — to replace damaged stem cells.

"Before the transplant, doctors give therapies such as chemo or radiation to eradicate the damaged cells to ready the body for the new ones,” says Jacques Azzi, director of the Inpatient BMT Unit at the Tisch Cancer Center at Mount Sinai in New York. “Bone marrow transplants can be from one’s own stem cells or from a donor. While called a transplant, it is actually an infusion of cells through a tube or catheter. Stem cells are injected and travel to the bone marrow, where they begin to produce healthy cells.”

What does it treat?

“A bone marrow transplant treats several blood, bone marrow, lymph node and plasma cancers including leukemias, multiple myelomas, myelodysplastic syndrome, lymphomas and myelofibrosis,” Azzi says. “It also treats other benign conditions such as sickle cell disease and aplastic anemia.”

In very rare cases, he notes, a bone marrow transplant is used in the treatment of certain solid tumors such as cancer of the cells in the body that develop into sperm and eggs.

What are the challenges of finding a bone marrow donor?

“To date, the biggest challenge in finding a bone marrow donor is ethnicity,” Azzi explains. “Ethnic minorities have a decreased chance of finding a fully matched donor in the registry.”

Ethnic minorities have about a 20% to 25% chance of finding a fully matched donor, while Caucasians have more than an 80% chance. This is particularly important, as the closer the match between the donor and recipient, the smaller the risk of GVHD.

What are the risks of a transplant, including GVHD?

“There are many risks directly related to the transplant procedure, including death, or as we call it in the field, non-relapse-related mortality, which simply means death from the actual transplant and not related to the underlying disease being treated,” Azzi says. “These deaths vary across transplant centers and while it was as high as 25% decades ago, it is less than 8% to 10% at most centers today.”

GVHD is one of the more common risks. It occurs when the newly generated immune system — as the result of the transplant — recognizes some of the patient’s normal cells as foreign, and attacks them.

Other risks of transplants include infections, fluid overload, inflammation and/or bleeding in the lungs, graft failure, viral infections, inflammation in the lungs and relapse of the original disease being treated by the transplant.

What are GVHD symptoms?

“Acute GVHD manifests as skin rash, redness and itching, diarrhea, nausea, abdominal pain and anorexia,” Azzi says, noting that it can more rarely affect the liver.

“Chronic GVHD, other than the underlying disease itself, is the most common cause of death following an allogeneic stem cell transplant,” says Azzi. “It is a slower process than acute GVHD and can affect any organ including the skin, mouth, esophagus, stomach, lungs, liver, eyes and joints.”

The key trait of GVHD is fibrosis resulting in limitation of range of movements, tightening of the skin, difficulty swallowing, eye dryness, chronic fatigue muscle weakness and chronic pain.

“Despite carrying significant risks and side effects, transplant remains the only curative option in several cancers,” says Azzi. “More recently, progress in supportive care, understanding GVHD and, in general, immunology have allowed for better outcomes and the ability to transplant older patients. More research is needed to better understand how to harness the immune system to attack and cure cancers while preventing the graft from attacking the host.”