A pensioner who has felt barely any pain throughout her life only realised her condition was unusual when she was 65.
She also experiences very little anxiety or fear, and may have enhanced wound healing.
Aged 65 she was found to have severe joint degeneration in her hip that had not even hurt her.
The year after she had surgery on her hand at Raigmore Hospital in Inverness and reported no pain, though the treatment is normally very painful.
Pain and anaesthetics specialist Dr Devjit Srivastava referred her to geneticists at University College London and the University of Oxford.
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They found two mutations, one in a gene known to be central to pain sensation, mood and memory. Mice without this gene have reduced pain, faster healing and reduced anxiety.
The woman, who wished to remain anonymous, experiences similar traits. Throughout her life she often did not notice burns until she could smell burning flesh and the injuries tended to heal very quickly. She got the lowest score on a common anxiety scale, and told researchers she never panics, even in dangerous situations.
Dr James Cox of UCL Medicine said: "We hope our findings might contribute to clinical research for post-operative pain and anxiety."
