Migraine sufferers were offered new hope today after researchers identified a faulty gene responsible for the debilitating headaches.
The finding could lead to better treatment and improve the quality of life for the one in five people who have the neurological disorder.
Scientists at the University of Oxford along with colleagues in Canada took DNA samples from migraines sufferers and their families.
They found that if a gene called Tresk is defective it can trigger pain nerves in the brain and cause a severe headache.
The discovery explains why people in the same family often suffer from the condition and could lead to new drugs that can switch off the pain.
Dr Zameel Cader, from the Medical Research Council's Functional Genomics Unit at the University of Oxford, said: "We have now made a major step forward in our understanding of why people suffer with migraine and how in certain cases, your family can literally give you a headache.
"Previous studies have identified parts of our DNA that increase the risk in the general population but have not found genes which can be directly responsible for common migraine.
"What we've found is that migraines seem to depend on how sensitive our nerves are in the pain centres of the brain.
"This finding should help lead to the key player which controls this excitability and will give us a real opportunity to find a new way to fight migraines and improve the quality of life for those suffering."
A migraine is a severe, long-lasting headache usually felt as a throbbing pain at the front or on one side of the head.
Some people can have a warning visual disturbance - for example, seeing zigzag lines or flashing lights - before the start of the headache which is called an aura.
Many people also have symptoms, such as nausea and sensitivity to light, during the headache itself.
Until now, the genes responsible were unknown.
The World Health Organisation (WHO) rates migraine as a leading cause of disability worldwide and it is estimated to be the most costly neurological disorder in Europe.
The study, published in Nature Medicine, was funded by the Medical Research Council, Genome Canada, Genome Quebec, Emerillon Therapeutics, the Wellcome Trust and Pfizer.