If you’ve ever stubbed your toe on a coffee table in the dead of night you know just how awesome it would be to switch off your sense of pain, if only for a moment. Unlike you and I, the Marsili family in Italy doesn’t fear stubbed toes, burns, or even broken bones. In fact, they don’t really sense pain at all, or at least not in the same way the rest of the world does, and scientists who have puzzled over the abnormality for years finally think they know why.

The family — more specifically, a grandmother, her two daughters, and a trio of grandchildren — has had to deal with the strange condition for decades, and while it might sound like a blessing to the rest of us, it’s actually more of a curse. Family members have endured some pretty serious injuries, including broken bones, without even realizing that it happened. After a new round of testing, researchers have pinpointed the cause, and it goes all the way to their genes.

The study, which was published in the journal Brain, put the family through some thorough testing in search of an answer. Their sensitivity to hot and cold was tested (surprise, they don’t have much feeling in that regard, either), and they appear almost entirely immune to most physical pain. At a loss for an explanation, scientists decided to dig through their genetics for a clue.

At long last, investigators discovered something amiss: a mutation in the ZFHX2 gene, which plays a role in how pain signals are interpreted by nerves and relayed to our brains, via other genes. The altered gene was present in each of the family members, so the team wanted to see if it was indeed the culprit.

The scientists tested mice which had been altered with the same mutated version of the gene that the Marsili family has naturally and found that they registered (or failed to register) pain in much the same way. In testing, the mice seemed to ignore what would have been painfully hot conditions, demonstrating that the altered gene was affecting them just as it has for three generations of the Marsili family.

The research not only answered a medical mystery for the Italian family, but could lead to breakthroughs in chronic pain management for individuals who suffer. Further research into how the gene affects pain reception could yield drugs which have the same effect, and improve the quality of life of countless patients.