Daniel Barbier

The child's parents first realized something was wrong when their 4-month-old developed severe teething sores, and two months later those first teeth fell out. The boy frequently bled from his mouth and lost more teeth when gnawing on toys. Then he bit off part of his tongue, with nary a whimper. He had other symptoms: minor wounds that wouldn't heal, ulcerations between his fingers, and he didn't scream when receiving injections. When X-rays revealed a previously undetected skull fracture, doctors diagnosed a hereditary sensory and autonomic neuropathy (HSAN).1

The boy had HSAN4, or congenital insensitivity to pain. Two mutations in the neurotrophic tyrosine kinase receptor type I (NTRK1) gene left his skin lacking nociceptors. The five HSANs, which vary by severity, age of onset, and mutated gene, vividly demonstrate that pain is vital. "People with inability to feel pain rarely make it past age 25....

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