By identifying the mutated gene that prevents the Marsili's from feeling discomfort, the researchers hope their findings will lead to the development of pain-killing drugs for people unable to get relief from existing treatments.
'They feel pain in the initial break but it goes away very quickly'
Certain family members experience slight pain, which fades within 50 to 60 seconds.
Dr Cox said: 'Sometimes they feel pain in the initial break but it goes away very quickly.
For example, Letizia broke her shoulder while skiing, but then kept skiing for the rest of the day and drove home. She didn't get it checked out until the next day.'
Some of the relatives are unable to sweat while others barely do so.
Yet, despite their tolerance to pain, they still report occasional headaches and lower-back pain, with the mothers also reporting discomfort during labour.
All of the relatives also have high sensitivity to odours, which is sometimes accompanied by vomiting or fainting.
Their intelligence and movement are unaffected.
Mutated gene could lead to new painkillers
The researchers performed a series of tests on the family members to determine their ability to feel pressure, detect temperature, notice heat from chillies and generally experience pain.
Results reveal all the relatives had a a mutation in a gene called ZFHX2. The number of nerves in their skin is normal.
When the researchers removed this gene in mice, they found the animals were worse at sensing painful pressure applied to their tails.
After the rodents were given the family's mutated gene, they became much less sensitive to heat.
ZFHX2 controls the activity of 16 other genes, some of which are involved in pain.
Working out how the gene reduces pain may help in the development of drugs that have the same effect, according to the researchers.
Such treatments could benefit those with chronic pain who do not get sufficient relief from existing therapies.
The findings were published in the journal Brain.
