Hugh Ham was just 1 year old when he developed a rash and fever. Doctors thought he had strep throat.

Ten days later, he was diagnosed with Kawasaki disease, a rare heart disease in young children that causes inflammation in blood vessels throughout the body. It can lead to aneurysms, or bulges, in the walls of the coronary arteries of the heart. These weakened areas can burst, develop deadly blood clots, or narrow with scar tissue.

Hugh’s parents, Matt and Tally Nelson, flew with him from Florida to Boston Children’s Hospital after the toddler was found to be one of a small number of patients who don’t respond to standard treatment. Doctors there stabilized him enough to go home.

For Hugh and every other child who’s developed the condition, the cause is unclear. It’s a mystery that has eluded scientists since Japanese pediatrician Tomisaku Kawasaki first described the disease in 1967.

But research has provided some valuable hints, according to a scientific statement issued Wednesday by the American Heart Association that provides recommendations for diagnosing and treating Kawasaki disease.

Researchers believe it may result from the body mounting an extreme immune response, especially in kids who may be genetically predisposed to developing the disease.

“We think that Kawasaki disease is related to some sort of infectious or environmental trigger that causes a huge immune response,” said Brian W. McCrindle, M.D., a cardiologist at Toronto’s Hospital for Sick Children who led the panel that wrote the statement. “We don’t know exactly what the trigger is.”

About 4,000 cases of Kawasaki disease occur each year in the United States, according to the Kawasaki Disease Foundation. The disease is most common among Asian, particularly Japanese, children, and it affects boys more often than girls.

Treatment includes an infusion of antibodies called immunoglobulins given within 10 days of the start of symptoms, which can include a high fever that lasts up to 10 days, bloodshot eyes, a red tongue and lips, a rash, and swollen lymph nodes. This infusion has been shown to dramatically decrease the risk of coronary artery aneurysms. The statement also recommends aspirin to reduce the risk of blood clots.

“It is important to educate the public as well as medical professionals about the signs and symptoms of Kawasaki disease because if there isn’t a timely diagnosis and treatment, the chances of long-term heart damage is greater,” said Kathryn Taubert, Ph.D., vice president of global strategies at the AHA, who helped develop the organization’s Kawasaki disease guidelines published in 2004. Taubert was not involved in the new statement.

McCrindle said finding the condition’s cause is the top priority for researchers, including Dr. Kawasaki himself, who is now in his 90s.

“Once we learn the cause, this might lead to more specific treatments and perhaps the possibility of preventing Kawasaki disease,” McCrindle said.

Kawasaki disease survivor Hugh Ham is now 2 years old. (Photo courtesy of Matt Nelson)

Kawasaki disease survivor Hugh Ham is now 2 years old. (Photo courtesy of Matt Nelson)

Doctors may misdiagnose it because it can mimic other more common illnesses, according to the statement. That’s what happened to Hugh, who is now 2 and loves to sing and dance.

Less than a year after his Kawasaki disease diagnosis, doctors discovered a large blood clot in one of Hugh’s coronary arteries, which could cause a fatal heart attack.

The Nelsons saw the image of the clot and broke down.

“It was the worst thing that could ever happen … scary in a different dimension,” Matt said. A blood thinner was added to Hugh’s regular treatment to help break up the clot. A few months later, it was gone.

One of his aneurysms is shrinking, but a second remains large and requires monitoring.

“Doctors and pediatricians need to be able to identify this prior to the 10-day [acute treatment] window,” Tally said. “It’s a deceiving disease and illness.”