“I truly have no clue,” SM (not pictured above) replied when asked what fear is. (Stock Photo: Getty Images)

President Franklin D. Roosevelt famously said, “The only thing we have to fear is fear itself.” But for individuals with Urbach-Wiethe syndrome, a rare hereditary genetic disorder, a worse fear exists: Some with the condition run the risk of having the inability to feel any fear at all.

NPR’s Invisibilia podcast recently spoke with a woman with Urbach-Wiethe, identified as SM to protect her identity, about what it’s like not only to be unable to experience fear but also to be unable to even understand the concept of fear.

“I truly have no clue,” SM replied when asked what fear is. In her lifetime, she has twice been held up at knifepoint and twice been held up at gunpoint. None of those experiences were traumatic for her.

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“Years ago, when my three sons were small,” explained SM in the podcast, “I was walking to the store, and I saw this man on a park bench. He said, ‘Come here, please.’ So I went over to him. I said, ‘What do you need?’ He grabbed me by the shirt, and he held a knife to my throat and told me he was going to cut me. I told him — I said, ‘Go ahead and cut me.’ And I said, ‘I’ll be coming back, and I’ll hunt your ass.’ … I wasn’t afraid. And for some reason, he let me go. And I went home.”

Were SM to sense fear, she most likely would not have approached the man on the bench, especially with three young children in tow. A life without biological fear exposes you to dangers that are easier to avoid if you do have fear.

There are only 400 known cases of Urbach-Wiethe, which causes the development of calcium deposits in the brain. In SM’s case, those deposits are on her amygdalae, the parts of the brain responsible for triggering one of the most basic evolutionary instincts, fight or flight. Because of SM’s condition, however, it’s as if her amygdalae don’t even exist.

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“Fear is an emotion you experience when you recognize that there is something in the environment that you ought to avoid and you have not yet successfully avoided it. The amygdala is a brain center that is crucial to circuits that allow people to integrate a lot of information, including information about things that should be avoided,” Art Markman, PhD, a psychologist at the University of Texas, tells Yahoo Health. “When this structure is damaged, people do not get that kind of basic information about things in the world to be avoided, and so they make bad decisions about what they ought to do.”

As a 2010 article in Psychology Today pointed out, “The amygdala is … an important source of the feeling that something isn’t quite right. By reminding us of potential risk and harm, this primitive center can actually put the brakes on other impulses.” Thus, those without normally functioning amygdalae run the risk of being unable to tell when they’ve acted inappropriately or, worse, putting themselves in harm’s way.

Despite the many self-help mantras that exhort us to live our lives free of fear, fear is in fact a necessary part of the human experience. Writes Kelly McGonigal, PhD, a health psychologist at Stanford University specializing in the mind-body connection, when thinking about how to live our proverbial best lives, “it’s a mistake to think the solution is to overcome fear in general. You can’t (at least, not without a temporal lobectomy). And even if you could, you wouldn’t like the results. We need our instincts to let us know when something is just wrong — an immediate emotional evaluation that is even more powerful than complex reasoning and logic.”

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Or, as Markman puts it, without fear, “we can often convince ourselves that even something that is probably a bad thing to do is worth trying. Often, what keeps us from doing something that might be dangerous is not our ability to reason, but our inability to overcome fear,” without which “there is nothing standing in our way when we convince ourselves that something we ought to be afraid of is something we should do.”

A 2011 study published in Current Directions in Psychological Science found that despite the perception that fear is a biological phenomenon, many fears are learned, as opposed to instinctual. Countering the belief that many people are afraid of snakes and spiders because of evolutionary instincts to avoid potentially poisonous things, the study’s researchers found that instead these are learned fears — and that they can be learned through conditioning in children as young as 7 months.

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