Aug. 15, 2012 -- It was hard enough for Karen Corby to hear that her autistic son would need a heart transplant to survive, but it was even harder to take the news that doctors wouldn't give him one.

"I was numb at first," Corby, of Pottsville, Pa., told ABCNews.com, remembering the phone call from Paul's cardiologist when she found out he wouldn't be placed on the transplant list. "Before she hung up, she told me to have a nice day."

Her son Paul, 23, has a left ventricle that didn't close after he was born, so his heart doesn't pump the right amount of blood. The Corbys found out in 2008, and were told it was time for a transplant in 2011.

The cardiologist at Penn Medicine told Corby that Paul was denied "given his psychiatric issues, autism, the complexity of the process, multiple procedures and the unknown and unpredictable effect of steroids on behavior," according to the letter Corby released.

Paul's experience raises questions about how autism and other brain disorders should be factored into transplant decisions.

"It seems that they have looked at this person as a label rather than the unique qualities that this person has," Dr. Dan Coury, Autism Speaks' Medical Director for the Autism Treatment Network, told ABCNews.com. Coury said he has not met Paul or reviewed his medical records, but he is aware of the rejection from a Philadelphia Inquirer story.

He said autism is one of many factors that should be considered in the transplant decision, but based on what he's read, he isn't sure why Paul was denied. He noted that Paul can carry on a conversation, has a good quality of life and has a social network to support him after the surgery.

Dr. David Cronin, an associate professor of transplant surgery at the Medical College of Wisconsin, told ABCNews.com he does not know the case, but organ transplant denial tends to be easier for people to accept because of an anatomic problem, such as calcified blood vessels that would prevent the successful implantation of a new kidney.

"Those no's are more acceptable than if somebody says, for example, 'You don't have enough insurance coverage,' or 'You still have behavioral problems like substance abuse issues,'" he said. "It's not like a CT scan where you can put it up and say,' Look. We can't technically do it.'"

Denials come because organs are a scarce resource, with three to four times as many people who need transplants as there are organs available. As such, he said, doctors look for transplant candidates to have good expected outcomes. For example, a dying patient who has a 1 percent chance of survival with a new organ would not be a good candidate because that organ could have gone to someone who could have lived a full life with it, he said.

The patient has to be able to take care of the new organ or have a support group to ensure that the organ doesn't go to waste, which can be an issue with mental illness, addiction and even autism, he said.

Cronin, who has not met Paul, said someone with a mental disorder could need to be restrained during surgery or rip out life-saving tubes and wires during recovery.

"I have never since 1995 seen that decision made in a cavalier fashion," Cronin said. "These decisions are not made in isolation. They're not made easily … We know the outcome is if someone is denied a transplant."

Penn Medicine was unable to comment on Paul's specific case, but said it reviews a number of factors before putting a patient on the transplant list.

"Our criteria for listing an individual for transplant are regularly reviewed in comparison with national standards, but we always encourage patients to seek another opinion," the statement concludes.

Patients who are denied can seek evaluation for the national waiting list at another transplant center in the hopes that the new center has a different criterion for choosing transplant candidates. Once the patient is on the national list, the United Network for Organ Sharing, a non profit contracted by the federal government matches donor organs to recipients.

As of 7:54 a.m. this morning, there were 114,852 people on the national list, according to the UNOS website. From January to May of this year, 11,468 transplants were performed, it said.

For now, Corby is accepting signatures on her Change.org petition and has mailed Paul's records to the Mayo Clinic for review. She also plans to send his records to the University of Pittsburgh's hospital.

"We don't want to get too hopeful, but it's better than where we were before," she said.