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Woman Not Afraid Of Anything, Even Danger, Due To Rare Genetic Disorder

Woman in sneakers on the rail of the railway
A U.S. woman laughs in the face of danger because she’s biologically unable to feel or recognize fear. Photo courtesy ofShutterstock

Imagine living a life without fear where poisonous spiders and snakes don’t make your skin cringe. One woman in the U.S. is actually biologically unable to feel fear, which leaves her susceptible to life-threatening situations. The 44-year-old fearless woman and mother of three, known as “SM” by a team of neuroscientists from the University of Iowa, was featured in this week’s NPR “Invisibilia” podcast to discuss what it’s like to live in a world without fear.

Dr. Daniel Tranel, of the University of Iowa, who conducted the interview, began by asking SM to describe fear. "Well, that's what I'm trying to — to be honest, I truly have no clue," she responds in a hoarse voice.

SM’s tone is actually a symptom of the condition that took away her fear. She was diagnosed with Urbach-Wiethe disease, which is characterized by three main symptoms: a hoarse voice, small bumps around the eyes, and calcium deposits in the brain. These deposits cause parts of the brain to calcify and harden, which can lead to epilepsy or other abnormalities, according to a previous 2011 study done on SM. For example, the amygdala, or almond-like structure found deep in the brain, calcifies and wastes away for the patient.

The fear response humans feel comes from the central nucleus of the amygdala, the region responsible for commands for bodily responses associated with fear, says The Dana Foundation, committed to advancing brain research and educating the public. Normally, the amygdala sends signals to the body to induce symptoms of fear such as a racing heart or sweaty palms. However, SM is literally unable to feel the emotion fear.

Tranel and his colleagues were able to eventually scare the fearless woman in 2013 when they made her inhale carbon dioxide. The amygdala is able to detect carbon dioxide at low concentrations in the body and triggers fear and panic as a sign of possible suffocation. SM did panic, in an unexpected way; she felt a sense of loss of control and unsteadiness, but no screaming.

So the question is: Is it better to have fear or be fearless? Based on one of SM’s terrifying experiences, a little bit of fear goes a long way.

SM was walking to the shop with her sons when a man on the park bench called her over. She said, “I told him — I said, ‘Go ahead and cut me.’ And I said, ‘I'll be coming back, and I'll hunt your ass.’” The man let her go and she went home, but she was unable to comprehend the danger and did not call the police after the event.

Though bizarre to almost anyone else, SM isn't completely different. She has a normal intelligence and is able to feel other emotions such as joy, sadness, and anger. But she just lacks the quick and subconscious response we all have when we’re in danger.

"I wonder what it's like, you know, to actually be afraid of something," she says.

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