Imagine being unable to feel any pain at all. For a tiny handful of people, that is the reality — and medical researchers have now pinpointed the mutation that removes their ability to perceive painful sensations.
The study began when doctors in northern Pakistan examined a remarkable group of related families in which several individuals seem entirely unaffected by pain. Their attention was first attracted by one member of the clan, a locally famous boy who performed street theatre involving walking on burning coals and stabbing his arms with knives.
Although it sounds like a party trick, the condition is devastating, as sufferers don't learn to know their limits. The street-performing boy killed himself on his fourteenth birthday after jumping off a house roof. The researchers studied six of his relatives, aged between 4 and 14 years. All had suffered many cuts and bruises, and injuries to lips and tongue caused by biting themselves; several had fractured bones without noticing.
This shows the importance of pain for our health and survival, notes Geoffrey Woods of the Cambridge Institute for Medical Research, UK, who led the study. "Pain is there for a jolly good reason — it stops us damaging ourselves," he says. For example, the pain from a broken arm or sprained ankle encourages us to rest that body part while it recovers.
The children in the study had no such safety check, causing them to be both graceless and reckless. "One girl was continually knocked down in the playground and just didn't mind at all," Woods says.
The researchers compared DNA samples from the six children and found that they all share a mutation in a gene called SCN9A, which is strongly expressed in nerve cells. They report their results in Nature.