Ashlyn Blocker was a happy baby. She never cried — not when she was born, not when she was hungry; not even when she severely burned her hand when she was 2 years old.

Her parents Tara and John, of Patterson, Ga., were getting ready to test their pressure washer when the phone rang. Tara ran inside to get it and when she returned, her daughter was standing by the machine’s running motor just looking at her hand. Ashlyn had touched the motor, completely burning the palm of her hand and the tips of her fingers. But she didn't cry. She didn't even grimace.

Slideshow: The Girl Who Can't Feel Pain

Tara held Ashlyn, who is now 11, in her lap – so upset at herself she began crying — when the unaffected 2-year-old told her, "It's going to be OK, Mommy."

Years later, Ashlyn’s happy demeanor was diagnosed as congenital insensitivity to pain, a rare, incurable disorder caused by the mutation of one or more genes that control pain sensitivity. Later research from the University of Florida revealed in 2009 that the affected gene in her case was SCN9A, which produces the molecule that is involved in directing nerve impulses to the brain. A mutation that causes this molecule not to function leads to the inability to feel pain, but if it becomes overactive, then it leads to severe pain.

"It is a genetic abnormality that makes it impossible for individuals to receive painful sensations," said Dr. Roland Staud, a pain expert and professor at the University of Florida College of Medicine, who led the study evaluating Ashlyn’s condition. "This has additional consequence that injuries that individuals have are not appreciated and not taken care of appropriately."

After appearing on a local television station to talk about Ashlyn’s case for a 2004 segment covering her story, Staud invited Ashlyn to come to the University of Florida to study her condition. Since 2004, Staud and a team of specialists have conducted a battery of physical, psychological, genetic and neurological tests on Ashlyn, her immediate family members and 10 control patients who feel pain normally.

In one test, in which Ashlyn was asked to rate the heat of an object, the researches realized that she could differentiate between warm and cold like everybody else. But when they ramped the temperature up or down to a level where the average person would begin to feel pain, she rated it as just warm, indicating that her mutations decreased, but did not abolish, her sensitivity to pain.

“She did really well like everybody else does, until it came to that threshold where the majority of people will say, ‘Yes, this is now turning into a painful stimulation,’” Staud said. “For her, there’s a block at a certain level on which she can’t perceive addition increase.”

Her specific mutation allows her to feel someone’s touch, but she doesn’t have the sense of smell.

Although her decreased sensitivity can occasionally come in handy — for instance, when her tickle-happy grandfather comes over – Staud concluded that pain is actually a gift.

“The life of someone who can’t appreciate pain is very difficult,” Staud said. “Look at pain as a warning signal that keeps you out of trouble and alerts you to the things you should try to stay away from.”

Even though the emergency room staff are now familiar with Ashlyn and her story, her condition continues to amaze them. She has only had to make three emergency room visits, but her list of minor injuries could match any toddler's worth their weight in Band-Aids.

Sometimes, it would be the minor complications that are normal during infancy, like the severe diaper rash Ashlyn had when she was 2 weeks old. But the complications were more often abnormal; for instance, she once stuck her pointer finger in her mouth and ripped the skin right off. While sleeping, she would chew on her lower lip, mutilating it to the point where it swelled so big, it covered her top lip as well. Another common injury is biting off the tip of the tongue.

"When she was a toddler, those were the toughest years because that's when a child is feeling their way through the world and they learn safety; like, 'OK, I fell down, I don't want to do that again.' They have that alarm system. Ashyln doesn't have that mechanism."

The first sign that made Ashlyn's parents take a closer look at the situation was when she was 6 months old, and her left eye became red and irritated. Their pediatrician thought it could be due to pink eye, but when antibiotics didn't work, an optamologist discovered she had a massive corneal abrasion.

Again, Tara held her young child in her lap, who was giggling and cooing as if nothing was wrong.

"Even to this day, we're pretty much Ashyln's pain mechanism, and we'll continue to be as long as we need to be," Tara said.

The first case of insensitivity to pain was reported in 1932, and only 45 to 50 have been diagnosed since, Staud said.

"What we know from history is the individuals that have congenital insensitivity to pain in the past came from Third-World countries… So, we are really, for the first time, actually seeing someone with this particular disorder in a Western civilization," he added.

Part of Staud’s research, which is available online and will be published in an upcoming edition of the European Journal of Pain, also evaluated Ashlyn’s sensitivity to emotional pain. While pain results from sensory stimuli, it also arises from emotional stimuli and Staud tried to determine whether she could relate and empathize with someone in pain.

“We often use pain terms when we describe our emotional state, and since she doesn’t experience pain, what does she use?” Staud asked.

They showed her a picture of someone in distress and asked her what she thought was happening. And, just like the day she consoled her distraught mother after burning her hand on the pressure washer, Ashlyn showed a degree of empathy and said she thought the person had been hurt.

Ashlyn’s ability to empathize is just one of her learned behaviors. Some she has picked up on her own, while others she has been taught.

“What we have tried over the six years is to teach her behavioral skills,” Staud said. “How you can live without pain in order to perceive some warning signals. So we have training sessions with her.”

Even with all the training in the world, Ashlyn is still at an increased risk for injury, which may not always be serious in nature, but may become serious when she doesn’t realize she has been injured and doesn’t get the treatment she needs.

For this reason, Tara tries to steer her away from the more risky activities. Recently, Tara had to tell Ashlyn she couldn’t try gymnastics. Ashlyn quickly moved on and found a safer alternative.

“She is in middle school now, and she brought a band form home. And I was so happy to sign that, you know, like, that's something we can actually say yes to,” Tara said.

Both Tara and Staud worry that Ashlyn won’t be able to feel chest pains later in life, or other warning signs of disease. Even more basically, Tara wonders if she will be able to tell if the milk or chicken has gone bad prior to the expiration date, or smell smoke if there’s a fire?

“I think her quality of life is likely to be very good,” said Staud, who will now open up testing to others. “She just has one sense less than we do. So I think she just has to err on the side of caution in many instances in her life. But I don't think this is the worst of all conditions she could have.”

Staud and his colleagues hope that their study will lead to new pain therapies, but they are cautious about tinkering with Ashlyn’s SCN9A gene because of the potential that it could cause the other extreme and lead to hypersensitivity to pain – a condition called paroxysmal extreme pain disorder.

But Staud is intrigued by the possibility of harnessing the SCN9A gene to create a genetic painkiller.

“We want to take a very close look at how we can chemically, or pharmacologically, induce the same changes in normal individuals,” he said. “And that's a very interesting direction to take because if we had a small molecule or a pharmacological agent that can block the transmission [of pain] the same way that Ashlyn can, then we have the perfect painkiller.”

As for Ashlyn, the start of school is likely her biggest concern right now.

“She is really a down to earth 11-year-old girl,” Tara said. “She looks and acts like your ordinary girl. It's just the way she's always been… And she always says, 'It's just me.' And that's the best way to describe it.”