A child street performer who could stick knives through his arms and walk on hot coals without feeling any pain has led to a genetic discovery that promises a new generation of safer and stronger painkillers.

The Pakistani boy and six of his young relatives had mutations in a single gene that left them incapable of experiencing pain, even though their sense of touch is normal.

All have suffered severe injuries as a result of not feeling pain. Two have bitten off parts of their tongues, and the performer died on his 14th birthday after jumping from a roof.

Their cases, however, are of huge medical significance and could help millions of people who suffer intractable pain.

The discovery of a single gene that can switch painful stimuli on and off without affecting other body systems raises the prospect of a new class of analgesics with none of the side-effects of conventional painkilling drugs. Neuroscientists said that the findings could ultimately prove as important as the discovery of the receptor for morphine.

The gene, SCN9A, is responsible for making a protein called a voltage-gated sodium channel, which seems essential to pain perception.

In normal people, this protein is found in high concentrations at the end of pain-sensing neurons. When a painful stimulus is felt, the protein amplifies it and excites the neuron, sending an electrical signal to the brain so that pain is felt.

The mutation disrupts this process, making the sodium channel protein useless. Painful stimuli thus fail to reach the pain-sensing neurons, and no signal is sent to the brain.

The discovery, by a team led by Geoffrey Woods, of the University of Cambridge, is particularly exciting because the abnormality appears to have no adverse effects in the children with the mutation, apart from the dangers that come with pain insensitivity.

This suggests that a drug that blocked the protein’s activity could fight pain without the side-effects that are produced by all the main analgesics available today.

Opioids such as morphine can cause respiratory problems, drowsiness and addiction, and can kill in overdose. Non-steroidal anti-inflammatories such as aspirin and ibuprofen can cause dangerous stomach bleeding, and COX-2 inhibitors such as Vioxx and Celebrex have been linked to heart damage.

John Wood, of University College London, a member of the study team, said: “The work of Geoff Woods and his team has provided us with an exciting new target for painkilling drugs — potentially this is as important as the identification of the morphine receptors.

“It will be a very difficult medical chemistry problem to make a drug that blocks only this sodium channel, but it is exciting to learn it might be possible.”

The findings also raise the prospect that other, smaller variations in the SCN9A gene could influence the way different people have different thresholds of pain tolerance.

In the research, which is published in the journal Nature, Dr Woods’s team identified the mutated SCN9A gene in six children from related families, who were aged between 4 and 14 when examined. The performer died before he could be tested, but his mother carried the mutation and Dr Woods is convinced that he had it.

None had ever been able to feel pain, though the older children had learnt to simulate pain in social situations in which others would expect them to feel it, including after football tackles. They were of normal intelligence and otherwise healthy, and could feel other tactile stimuli such as touch, pressure, temperature and tickling.

“All six affected individuals had never felt any pain, at any time, in any part of their bodies,” Dr Woods said. “They would walk awkwardly and bump into things as they didn’t get hurt, they were covered in bruises.” Dr Woods said. “They wear out their bodies. Life without pain sounds like a blessing, but it isn’t.”

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