CHICAGO -- Deb McGarry had just delivered the eulogy at her grandmother's funeral when pain shot through her chest. A wave of nausea followed.

"Something is wrong," McGarry whispered to her husband as an arm went numb and the lump in her throat turned to panic.

McGarry, a mother of two from Naperville, Ill., suffered a heart attack a few hours later in an emergency room. She was diagnosed with a rare coronary condition that can affect otherwise healthy young women and is often fatal.

Stricken in January 2011, McGarry left the hospital after five days feeling isolated and confused. Finding information about the ailment -- "spontaneous coronary artery dissection," or SCAD -- was difficult and doctors were unable to help, she said.

McGarry eventually discovered a thriving online community that provided details about her condition and, more important, encouragement. With a few clicks of a mouse, she was able to plug into a wealth of information and support.

From places as far away as New Zealand, Australia and the United Kingdom, these survivors are part of patient-driven revolution in the world of rare diseases who mobilize through social networks, experts say.

"With rare diseases, you can't walk in to your doctor's office and find the support and information you need," said McGarry, 39. ".It's absolutely amazing to be able to get on your computer and find people who are experiencing the same thing as you."

Social networks increasingly are playing a role in medical projects. Here are a few recent examples:

Researchers at the University of Utah are mining social networking sites to identify the vocabulary and new health terms used by people who talk about their conditions online.

Boston Children's Hospital partnered with the online community TuDiabetes to design software that protects user privacy while allowing individuals to chart their blood sugar levels for research purposes.

PatientsLikeMe, a health data-sharing website with more than 100,000 members, used social networks to conduct real-time evaluations during a drug trial.

Experts caution that the Internet is a double-edged sword. Although people find support, they also can be scammed and seduced into believing information that isn't true -- especially on sites that aren't sponsored by hospitals or a medical institution.

Thanks to efforts by McGarry and the on-line network of SCAD survivors, doctors at the Mayo Clinic in Rochester, Minn., have launched the first large-scale research project to learn more about the disease.

The study is breaking new ground by using social media to recruit SCAD patients from around the world, doctors say. The plan is to input each individual's medical history into a database in hopes of identifying patterns.

The Mayo Clinic also will create a bio-bank of blood samples from patients with SCAD, along with samples from their parents and children.

The hope is that it may lead to answers about the role genetics plays in the disease, said Dr. Sharonne Hayes, director of Mayo Clinic Women's Heart Clinic.

The methods used could have applications for many other rare diseases, she said.

"This goes far beyond SCAD," Hayes said.

Spontaneous coronary artery dissection begins with an unexplained tear inside the artery wall. The loose tissue folds over, blocking blood flow and leading to clots, arterial blockage and often a heart attack.

According to Mayo Clinic doctors, little research has been done on the disease, which has no cure or standard treatment. So far, doctors can't say with much certainty what causes the condition, whether it is likely to recur or if it can be passed along genetically.

For many, not knowing such crucial details can be as debilitating as the physical symptoms, patients said.

In McGarry's case, when she arrived at the emergency room almost two years ago, doctors could find nothing wrong with her, she said. But an hour later, surrounded by friends and family, McGarry suffered a heart attack. Doctors implanted two stents to open up the artery, then sent her home several days later with more questions than answers, she said.

"I was freaking out; I immediately got online," said McGarry, recalling the anxiety she felt as she entered the search terms into a web browser for the first time.

According to the National Institutes of Health, a rare disease is one that affects fewer than 200,000.

The institute tracks roughly 7,000 diseases considered rare and coordinates and supports research, according to the NIH website.

A 2011 study by the Pew Internet and American Life Project found that one in five Americans uses the Internet to find people with similar health concerns.

"We have this ancient instinct to find other people who share our same problems so we can solve them together," said the project's associate director, Susannah Fox. With the Internet "it's faster and easier, but it's that same old wish."

For patients and those who care for them, social networks can offer solace from what can be a lonely battle for survival, Fox said.

At the same time, patients who organize themselves in cyberspace can offer new opportunities for researchers.

"The real magic happens when someone with a great idea is able to connect with one of these patient groups who stand ready and willing to help," Fox said.

McGarry's "SCAD sisters," as she calls them, started their odyssey in an online discussion group created by WomenHeart, the National Coalition for Women with Heart Disease.

The group's website includes a disclaimer.

"The community board is offered as a place where women can share their stories," it states. "It is not intended to be a source of medical advice and is not monitored by doctors or other experts."

In the Information Age, the consumer adage, "buyer beware," still applies.

"It's really patient beware," said Stefanie Putkowski, a nurse with the National Organization of Rare Diseases, or NORD.

Nearly 30 million Americans suffer from rare diseases, according to NORD, a nonprofit group that aims to help patients and their caregivers through education, research and other services.

Putkowski polices the many online organizations and message boards the organization sponsors under the name "NORD Nurse."

Although she believes the web is a key ingredient in medical innovation and treating a myriad of rare diseases, the Internet can also be a dangerous place where misinformation prevails and scammers prey on the vulnerable, she said.

"If you are desperate and not savvy, you can spend your money and waste it, and you can get hurt," said Putkowski. "But if it's a good organization, it can be a lifesaver. Short of getting a treatment or a cure, at least you are not alone."

Forced to become advocates, some like Bob Alico, who lost his wife to the disease in 2010, try to leverage the online community to influence research, raise funds and organize events.

Alico of Scottsdale, Ariz., founded SCAD Research Inc. and also helped organize the SCAD Survivors Reunion, which held a 5-K walk held last month in Naperville, where the couple used to live.

As he planned the event, Alico started notifying survivors and possible donors through the social network. A buzz was quickly created, and he was able to nail it down within a few months, he said.

"That's the social network -- boom!" said Alico. "The chances of all of this happening were extraordinarily small, but it worked."

Patients with rare diseases tend to find one another and connect because they are searching for information and support, said Dr. Marysia Tweet of the Mayo Clinic.

"Studies of rare disease often are underfunded, and people with these conditions are quite motivated," she said.

The Mayo Clinic's Hayes joined Alico and more than 150 others from all over the country for the walk through the Springbrook Prairie Forest Preserve to raise the profile of SCAD.

After the walk, Hayes detailed the study's latest findings, including that nearly 70 percent of the cases strike women.

The patients, most of whom had never met face-to-face, spent the day basking in the sense of community.

"The whole social media thing is really cool," McGarry said. "But to get a hug from someone, it's totally different."